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Park JH, Park YS, Lee MH, Rhim SY, Song JC, Lee SJ, Kim JM, Shaw LM, Kang JS. Determination of plasma topiramate concentration using LC-MS/MS for pharmacokinetic and bioequivalence studies in healthy Korean volunteers. Biomed Chromatogr 2008; 22:822-9. [DOI: 10.1002/bmc.995] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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152
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Dixon R, Job S, Oliver R, Tompson D, Wright JG, Maltby K, Lorch U, Taubel J. Lamotrigine does not prolong QTc in a thorough QT/QTc study in healthy subjects. Br J Clin Pharmacol 2008; 66:396-404. [PMID: 18662287 DOI: 10.1111/j.1365-2125.2008.03250.x] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
AIM To characterize the effects of lamotrigine on QT interval in healthy subjects. METHODS Healthy subjects received a single oral dose of moxifloxacin (400 mg) or placebo in crossover design, followed by a dose-escalating regimen of lamotrigine (n = 76) over a 77-day period, or matched placebo (n = 76). Blood samples were taken for determination of moxifloxacin and lamotrigine concentrations and digital 12-lead ECGs were recorded. The relationships between individual QT values and respective individual moxifloxacin or lamotrigine concentrations were explored using population pharmacokinetic-pharmacodynamic (PK-PD) modelling. RESULTS Moxifloxacin was associated with a maximum mean increase from baseline in QTcF of 14.81 ms [90% confidence interval (CI) 13.50, 16.11] 2.5 h after dosing. Steady-state exposure to lamotrigine (50, 150 or 200 mg b.d.) was not associated with an increase in QTc interval. Small reductions in QTcF (maximum mean difference from placebo -7.48 ms, 90% CI -10.49, -4.46) and small increases in heart rate (maximum mean difference from placebo 5.94 bpm, 90% CI 3.81, 8.06) were observed with lamotrigine 200 mg b.d. vs. placebo. No effect of lamotrigine on QRS duration or blood pressure was observed. No outliers with QTcF > 450 ms, or with an increase from baseline of >60 ms were observed in the lamotrigine group. PK-PD modelling indicated statistically significant decreases in individually corrected QT intervals for lamotrigine and statistically significant increases in individually corrected QT intervals for moxifloxacin over the concentration ranges studied. CONCLUSIONS Therapeutic doses of lamotrigine (50-200 mg b.d.) were not associated with QT prolongation in healthy subjects.
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Affiliation(s)
- Ruth Dixon
- Department of Clinical Pharmacology and Discovery Medicine, Discovery Biometrics, GlaxoSmithKline, Harlow, UK
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153
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Abstract
Therapeutic drug monitoring (TDM) of antiepileptic drugs (AEDs) has made it possible to study the individual variations in drug utilization, to reveal noncompliance in patients and for quality assurance aspects. Even if there is a shortage of data from randomized controlled studies concerning the effectiveness of using TDM as an aid to dosage adjustment, experience from nonrandomized investigations and long-lasting clinical experience have shown that TDM of both older and newer AEDs may be of clinical benefit if used appropriately. The main situations for TDM include: after starting treatment to provide a baseline steady-state concentration for further evaluation of an individual therapeutic concentration; after change in drug dosage, in particular when nonlinear kinetics apply; at therapeutic failure to sort out a pharmacokinetic explanation for uncontrolled seizures or side effects; in case of drug interactions; and when pharmacokinetic changes due to physiological or pathological changes are foreseen (e.g., age-dependent conditions [children, elderly], pregnancy, hepatic disease, renal disease or gastrointestinal conditions potentially affecting drug absorption) and change in drug formulation (brand name/generic). Recently, new terminology and definitions have been suggested by the International League Against Epilepsy. The reference range is a range of drug concentrations quoted by laboratories and is not a therapeutic range. Emphasis should be placed on the concept of an individual therapeutic concentration.
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Affiliation(s)
- Svein I Johannessen
- The National Center for Epilepsy, Sandvika, Division of Clinical Neuroscience, Rikshospitalet University Hospital, Oslo, POB 53, N-1306 BPT, Norway.
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Søndergaard Khinchi M, Nielsen KA, Dahl M, Wolf P. Lamotrigine therapeutic thresholds. Seizure 2008; 17:391-5. [DOI: 10.1016/j.seizure.2007.11.023] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2007] [Revised: 09/12/2007] [Accepted: 11/20/2007] [Indexed: 10/22/2022] Open
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155
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High-Speed Simultaneous Determination of Nine Antiepileptic Drugs Using Liquid Chromatography-Mass Spectrometry. Ther Drug Monit 2008; 30:347-56. [DOI: 10.1097/ftd.0b013e3181678ecb] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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156
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Linnet K, Steentoft A, Simonsen KW, Sabers A, Hansen SH. An oxcarbazepine-related fatality with an overview of 26 oxcarbazepine postmortem cases. Forensic Sci Int 2008; 177:248-51. [DOI: 10.1016/j.forsciint.2007.10.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2006] [Revised: 10/11/2007] [Accepted: 10/13/2007] [Indexed: 11/28/2022]
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157
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Pharmacokinetic, Pharmacodynamic, and Pharmacogenetic Targeted Therapy of Antiepileptic Drugs. Ther Drug Monit 2008; 30:173-80. [DOI: 10.1097/ftd.0b013e318167d11b] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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158
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Pharmacological disruption of calcium channel trafficking by the alpha2delta ligand gabapentin. Proc Natl Acad Sci U S A 2008; 105:3628-33. [PMID: 18299583 DOI: 10.1073/pnas.0708930105] [Citation(s) in RCA: 299] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The mechanism of action of the antiepileptic and antinociceptive drugs of the gabapentinoid family has remained poorly understood. Gabapentin (GBP) binds to an exofacial epitope of the alpha(2)delta-1 and alpha(2)delta-2 auxiliary subunits of voltage-gated calcium channels, but acute inhibition of calcium currents by GBP is either very minor or absent. We formulated the hypothesis that GBP impairs the ability of alpha(2)delta subunits to enhance voltage-gated Ca(2+)channel plasma membrane density by means of an effect on trafficking. Our results conclusively demonstrate that GBP inhibits calcium currents, mimicking a lack of alpha(2)delta only when applied chronically, but not acutely, both in heterologous expression systems and in dorsal root-ganglion neurons. GBP acts primarily at an intracellular location, requiring uptake, because the effect of chronically applied GBP is blocked by an inhibitor of the system-L neutral amino acid transporters and enhanced by coexpression of a transporter. However, it is mediated by alpha(2)delta subunits, being prevented by mutations in either alpha(2)delta-1 or alpha(2)delta-2 that abolish GBP binding, and is not observed for alpha(2)delta-3, which does not bind GBP. Furthermore, the trafficking of alpha(2)delta-2 and Ca(V)2 channels is disrupted both by GBP and by the mutation in alpha(2)delta-2, which prevents GBP binding, and we find that GBP reduces cell-surface expression of alpha(2)delta-2 and Ca(V)2.1 subunits. Our evidence indicates that GBP may act chronically by displacing an endogenous ligand that is normally a positive modulator of alpha(2)delta subunit function, thereby impairing the trafficking function of the alpha(2)delta subunits to which it binds.
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159
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Shank RP, Maryanoff BE. Molecular pharmacodynamics, clinical therapeutics, and pharmacokinetics of topiramate. CNS Neurosci Ther 2008; 14:120-42. [PMID: 18482025 PMCID: PMC6494007 DOI: 10.1111/j.1527-3458.2008.00041.x] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Topiramate (TPM; TOPAMAX) is a broad-spectrum antiepileptic drug (AED) that is approved in many world markets for preventing or reducing the frequency of epileptic seizures (as monotherapy or adjunctive therapy), and for the prophylaxis of migraine. TPM, a sulfamate derivative of the naturally occurring sugar D-fructose, possesses several pharmacodynamic properties that may contribute to its clinically useful attributes, and to its observed adverse effects. The sulfamate moiety is essential, but not sufficient, for its pharmacodynamic properties. In this review, we discuss the known pharmacodynamic and pharmacokinetic properties of TPM, as well as its various clinically beneficial and adverse effects.
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Affiliation(s)
- Richard P. Shank
- Research & Early Development, Johnson & Johnson Pharmaceutical Research & Development, Spring House, Pennsylvania 19477‐0776 USA
| | - Bruce E. Maryanoff
- Research & Early Development, Johnson & Johnson Pharmaceutical Research & Development, Spring House, Pennsylvania 19477‐0776 USA
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161
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Svalheim S, Taubøll E, Surdova K, Ormel L, Dahl E, Aleksandersen M, McNeilly A, Gjerstad L, Ropstad E. Long-term levetiracetam treatment affects reproductive endocrine function in female Wistar rats. Seizure 2007; 17:203-9. [PMID: 18155931 DOI: 10.1016/j.seizure.2007.11.018] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Abstract
PURPOSE Several antiepileptic drugs (AEDs) induce changes in endocrine function in women with epilepsy. Levetiracetam (LEV) is one of the newer AEDs, and to date no endocrine side-effects have been reported in humans. However, a recent study on ovarian follicular cells from prepubertal pigs showed that LEV affected basal steroid hormone secretion. The aim of the present study was to investigate possible effects of the drug on endocrine function and ovarian morphology in non-epileptic rats. METHODS Thirty female Wistar rats were fed per-orally with either 50mg/kg LEV (n=15) or 150 mg/kg LEV (n=15) twice daily for 90-95 days. Twenty rats received a control solution. The rats were killed in the dioestrus phase of the oestrous cycle. Serum concentrations of testosterone, 17beta-oestradiol, progesterone, follicle stimulating hormone (FSH), luteinizing hormone (LH) and LEV were measured, and the ovaries examined histologically. RESULTS Mean ovarian weight showed a significant, dose-dependent increase after LEV treatment. Mean numbers of ovarian follicular cysts were not changed, but the numbers of corpora lutea and secondary follicles were significantly higher in the treated animals. Serum testosterone was significantly increased in treated animals (0.50 nmol/l versus 0.16 nmol/l in controls, p<0.05), while oestradiol was reduced (67.4 compared to 257.5 pmol/l in controls, p<0.05). The low-dose group had significantly lower serum progesterone concentrations than the control group (56.8 nmol/l versus 34.7 nmol/l, respectively, p<0.05). FSH was reduced in the treated animals (3.3 ng/ml versus 5.5 ng/ml, p<0.05) while LH was unaffected. CONCLUSION Our findings indicate a possible effect of LEV on the hypothalamic-pituitary-gonadal (HPG) axis and ovarian morphology in non-epileptic rats. The effects differ from those previously described for other AEDs. Caution must be taken before these results can be applied to humans.
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Affiliation(s)
- Sigrid Svalheim
- Department of Neurology, Division of Clinical Neuroscience, Rikshospitalet Medical Centre, Rikshospitalet, 0027 Oslo, Norway.
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162
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Lancelin F, Franchon E, Kraoul L, Garciau I, Brovedani S, Tabaouti K, Landré E, Chassoux F, Paubel P, Piketty ML. Therapeutic drug monitoring of levetiracetam by high-performance liquid chromatography with photodiode array ultraviolet detection: preliminary observations on correlation between plasma concentration and clinical response in patients with refractory epilepsy. Ther Drug Monit 2007; 29:576-83. [PMID: 17898647 DOI: 10.1097/ftd.0b013e318157032d] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Levetiracetam is a new antiepileptic drug prescribed for the treatment of patients with refractory partial seizures with or without secondary generalization as well as for the treatment of juvenile myoclonic epilepsy. A rapid and specific method by high-performance liquid chromatography diode array detection was developed to measure the concentration of levetiracetam in human plasma. The trough plasma concentrations measured in 69 epileptic patients treated with 500 to 3000 mg/d of levetiracetam ranged from 1.1 to 33.5 microg/mL. The mean (range) levetiracetam plasma concentrations in responders and nonresponders were 12.9 microg/mL (4.6-21 microg/mL) and 9.5 microg/mL (1.1-20.9 microg/mL), respectively. A wide variability in concentration-response relationships was observed in patients. Using a receiver operating characteristic curve, the threshold levetiracetam concentration for a therapeutic response was 11 microg/mL. The sensitivity and specificity for this threshold levetiracetam concentration were 73% and 71%, respectively. According to chi analysis, this finding was not significant probably because of the small number of patients and because of their refractory seizure type. Nevertheless, the levetiracetam plasma concentration could be used to help clinicians detect severe intoxication or to verify compliance by repeating the measurement in patients.
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163
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Zemke D, Farooq MU, Gupta R, Kassab M, Reeves M, Majid A. The Effect of Anticonvulsant Drugs on the Fibrinolytic Activity of Tissue Plasminogen Activator. Cerebrovasc Dis 2007; 25:107-10. [DOI: 10.1159/000111999] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2007] [Accepted: 08/29/2007] [Indexed: 11/19/2022] Open
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Kim JS, Kondratyev A, Tomita Y, Gale K. Neurodevelopmental impact of antiepileptic drugs and seizures in the immature brain. Epilepsia 2007; 48 Suppl 5:19-26. [PMID: 17910577 DOI: 10.1111/j.1528-1167.2007.01285.x] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Seizure incidence during the neonatal period is higher than any other period in the lifespan, yet we know little about this period in terms of the effect of seizures or of the drugs used in their treatment. The fact that several antiepileptic drugs (AEDs) induce pronounced apoptotic neuronal death in specific regions of the immature brain prompts a search for AEDs that may be devoid of this action. Furthermore, there is a clear need to find out if a history of seizures alters the proapoptotic action of the AEDs. Our studies are aimed at both of these issues. Phenytoin, valproate, phenobarbital, and MK801 each induced substantial regionally specific cell death, whereas levetiracetam even in high doses (up to 1,500 mg/kg) did not have this action. In view of our previously findings of neuroprotective actions of repeated seizures in the adult brain, we also examined repeated seizures for a possible antiapoptotic action in the infant rat. Rat pups were preexposed to electroshock seizures (ECS) for 3 days (age 5-7 days) before receiving MK801 on day 7. The effect of ECS, which was consistently a 30% decrease in MK801-induced programmed cell death (PCD), suggests that repeated seizures can exert an antiapoptotic action in the infant brain. In contrast, PCD induced by valproate was not attenuated by ECS preexposure, suggesting that valproate-induced PCD is mechanistically distinct from that induced by MK801 and may not be activity-dependent. Presently, we do not know if this neuroprotective effect of seizures is deleterious or beneficial. If the seizures also enhance the survival of neurons that are destined to undergo naturally occurring PCD, early childhood seizures may have deleterious effects by preventing this necessary component of normal development. While this effect of seizures might be counteracted by AEDs, the fact that several AEDs shift the PCD to the other extreme, and trigger excessive neuronal cell loss, raises concern about whether the drug therapy may be more detrimental than the seizures. In this context, it is encouraging that we have identified at least one AED that is devoid of a proapoptotic action in the infant brain, even in high doses. It is now important to evaluate the long-term consequences of the changes in PCD in infancy by examining behavioral outcomes and seizure susceptibility in the AED- and seizure-exposed neonates when they reach adulthood.
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Affiliation(s)
- Jin-Sook Kim
- Interdisciplinary Program in Neuroscience & Department of Pharmacology, Georgetown University, Washington, DC, USA
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165
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Otoul C, De Smedt H, Stockis A. Lack of Pharmacokinetic Interaction of Levetiracetam on Carbamazepine, Valproic Acid, Topiramate, and Lamotrigine in Children with Epilepsy. Epilepsia 2007; 48:2111-5. [PMID: 17651416 DOI: 10.1111/j.1528-1167.2007.01201.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE To determine whether levetiracetam (LEV) affects plasma concentrations of carbamazepine, valproic acid, topiramate, and lamotrigine in children with epilepsy. METHODS The potential for interaction of LEV with other antiepileptic drugs (AEDs) was assessed using plasma drug levels obtained in a randomized placebo-controlled phase III trial of adjunctive LEV in children receiving one or two concomitant AEDs. Multiple plasma AED levels at baseline and during adjunctive treatment with LEV or placebo were compared by repeated measures analysis of covariance and mean concentration ratios (treatment/baseline) were estimated with their 90% confidence intervals (CI). RESULTS The study population included 187 children receiving any concomitant AED alone or in combination. The geometric mean concentrations at baseline and during LEV treatment were carbamazepine 8.4 microg/ml versus 8.1 microg/ml (coefficient of variation, CV = 30%; n = 35); valproic acid 83.8 versus 82.5 microg/ml (CV = 38%; n = 23); topiramate 7.3 versus 7.2 microg/ml (CV = 82%; n = 28); lamotrigine 8.2 versus 7.7 microg/ml (CV = 62%; n = 22). For each AED, the mean concentration ratios (LEV/baseline) and their 90% CIs showed that AED concentrations were unaffected by concomitant LEV administration. No differences were observed between LEV and placebo. CONCLUSIONS LEV does not affect plasma concentrations of carbamazepine, valproic acid, topiramate, or lamotrigine in children with epilepsy.
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166
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West CL, Mealey KL. Assessment of antiepileptic drugs as substrates for canine P-glycoprotein. Am J Vet Res 2007; 68:1106-10. [DOI: 10.2460/ajvr.68.10.1106] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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167
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Nissen-Meyer LSH, Svalheim S, Taubøll E, Reppe S, Lekva T, Solberg LB, Melhus G, Reinholt FP, Gjerstad L, Jemtland R. Levetiracetam, Phenytoin, and Valproate Act Differently on Rat Bone Mass, Structure, and Metabolism. Epilepsia 2007; 48:1850-60. [PMID: 17634065 DOI: 10.1111/j.1528-1167.2007.01176.x] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
PURPOSE Long-term treatment with antiepileptic drugs (AEDs) is associated with increased risk of fractures. Phenytoin (PHT) and valproate (VPA) have both been suggested to influence bone health, whereas levetiracetam (LEV) is scarcely studied. The present study compares the effect of these AEDs on bone mass, biomechanical strength, and bone turnover in rats. METHODS Female rats received PHT (50 mg/kg), VPA (300 mg/kg), or LEV (50 and 150 mg/kg) for 90 days. Dissected femurs were analyzed using dual energy x-ray absorptiometry (DXA), three-point cantilever bending, and histomorphological evaluation. Serum levels of biochemical bone turnover markers were monitored using immunoassay quantification. RESULTS PHT and VPA reduced bone mineral density (BMD) and content (BMC) in one or more bone compartments, whereas LEV did not. VPA induced increased bone turnover, whereas modest changes were observed for PHT. Interestingly, low-dose LEV was associated with reduced biomechanical strength of the femoral neck (mainly trabecular bone). In addition, low-dose LEV treatment resulted in significantly reduced levels of serum osteocalcin, a marker of bone formation. Histomorphological analyses indicated increased retention of cartilage remnants at the growth plate metaphysis of rats treated with low-dose LEV vs. controls. CONCLUSIONS PHT, VPA, and LEV exert differential effects on bone mass and strength, suggesting different mechanisms of action. The weakening effect of low-dose LEV on the femoral neck, despite a constant BMD, suggests a primary effect on bone quality. These findings warrant further human studies of possible adverse effects of LEV on bone development and growth, particularly in children and adolescents.
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168
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Snoeck E, Jacqmin P, Sargentini-Maier ML, Stockis A. Modeling and simulation of intravenous levetiracetam pharmacokinetic profiles in children to evaluate dose adaptation rules. Epilepsy Res 2007; 76:140-7. [PMID: 17851036 DOI: 10.1016/j.eplepsyres.2007.07.011] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2007] [Revised: 06/17/2007] [Accepted: 07/23/2007] [Indexed: 10/22/2022]
Abstract
PURPOSE To develop a pharmacokinetic model for intravenous levetiracetam in children, based on adult intravenous data and pediatric oral data. METHODS Data from two adult Phase-I studies in which levetiracetam was given intravenously were utilized to develop the adult population pharmacokinetic two-compartment intravenous model. After model qualification, combination with an existing pediatric one-compartment oral population pharmacokinetic model enabled simulation of twice-daily intravenous infusions of levetiracetam in children. Median and 90% confidence intervals for C(trough), C(max) (end of infusion) and AUC(tau) were simulated for 2000 children and compared to the values observed in adults. RESULTS The population pharmacokinetic two-compartment model successfully described intravenous levetiracetam pharmacokinetics in healthy adults. After combination with the oral pediatric population model, steady-state concentrations at the end of 15-, 30- and 60 min b.i.d. levetiracetam intravenous infusions in children were predicted to be 29-41, 17-24 and 6-13% higher than those observed after oral dosing of 30 mg/kg b.i.d. Concentrations returned to the range of oral exposures within 1h after the infusion peak. The combined model predicted that steady-state peak plasma concentrations and AUC(tau) in children receiving 30 mg/kg twice daily as 15 min intravenous infusions were within the range of predicted and observed C(max,ss) and AUC(tau )values of adults receiving 15 min intravenous infusions of 1500 mg levetiracetam. CONCLUSIONS The simulations suggest that levetiracetam may be administered intravenously in children as 15 min infusions.
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169
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Abstract
The availability of generic products of antiepileptic drugs (AEDs) has raised the following concerns: (1) Do generic AEDs work as well as brand AEDs in terms of their efficacy, safety and quality? (2) Can generic AEDs be used as substitutions for brand AEDs? and (3) Can generic products of AEDs be used interchangeably? The traditional average bioequivalence analysis addresses concern 1 but does not provide a complete adequate response to concerns 2 and 3. Drug interchangeability can be classified as drug prescribability or drug switchability. Drug prescribability refers to the situation where a patient is treated for the first time so that either a brand or a bioequivalent generic AED can be chosen. Drug switchability refers to the situation in which a brand AED is switched to a bioequivalent generic product of the same AED. The traditional average bioequivalence approach is sufficient to evaluate the prescribability of generic products, but does not ensure the switchability between prescribable formulations. The necessity of assuring switchability of two formulations can be addressed by individual bioequivalence. While the switch to generic AEDs is well tolerated by many patients and in general cost-effective, seizure control should not be sacrificed on the basis of cost alone, as the major end point in treating epilepsy with AEDs is seizure control without side effects. Until we have individual (within patient) bioequivalence data on generic AEDs and/or the tools to a priori identify the subset of patients susceptible to the generic switch, a switch of AED products in seizure-free patients is not recommended.
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Affiliation(s)
- Meir Bialer
- Department of Pharmaceutics, School of Pharmacy and David R. Bloom Center for Pharmacy, Faculty of Medicine, The Hebrew University of Jerusalem, Jerusalem, Israel.
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170
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von Borstel Smith M, Crofoot K, Rodriguez-Proteau R, Filtz TM. Effects of phenytoin and carbamazepine on calcium transport in Caco-2 cells. Toxicol In Vitro 2007; 21:855-62. [PMID: 17412555 DOI: 10.1016/j.tiv.2007.02.008] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2006] [Revised: 01/24/2007] [Accepted: 02/19/2007] [Indexed: 11/16/2022]
Abstract
Adverse effects of anti-seizure/anti-epileptic medications on bone density have been observed and reported since the early 1960s. Phenytoin and carbamazepine are two commonly prescribed anti-epileptic drugs most frequently associated with osteomalacia including fractures, bone demineralization, and reduced bone formation. The mechanism by which anti-epileptic drugs induce bone loss is not fully explained. We hypothesized that anti-epileptic drugs may impair dietary calcium absorption in the intestine. Using Caco-2 cells, a model transport system for study of the function of the intestinal epithelium, we determined the effects of several anti-epileptic drugs on intestinal epithelial calcium transport. In our system, phenytoin and carbamazepine dose-dependently inhibit active calcium transport from the apical to basolateral side of Caco-2 cells under physiologic calcium conditions. Vitamin D ameliorates the anti-epileptic drug-induced decrease in calcium permeability.
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Affiliation(s)
- Melinda von Borstel Smith
- Department of Pharmaceutical Sciences, College of Pharmacy, Oregon State University, Corvallis, OR 97330, USA
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171
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Malakova J, Brozmanova H, Vorisek V, Prochazkova V, Palicka V. A Capillary GC Method Using Nitrogen Phosphorus Detection for Determination of Topiramate in Patients with Epilepsy. Chromatographia 2007. [DOI: 10.1365/s10337-007-0310-y] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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172
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Hirsch LJ, Arif H, Buchsbaum R, Weintraub D, Lee J, Chang JT, Resor SR, Bazil CW. Effect of Age and Comedication on Levetiracetam Pharmacokinetics and Tolerability. Epilepsia 2007; 48:1351-9. [PMID: 17573925 DOI: 10.1111/j.1528-1167.2007.01043.x] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
PURPOSE To compare pharmacokinetics and tolerability of levetiracetam (LEV) in older versus younger adults. METHODS As part of the Columbia Antiepileptic Drug Database, we retrospectively studied the pharmacokinetics and tolerability of LEV in patients who had been seen as an outpatient at our center during a 4-year period. We compared apparent clearance (CL) of LEV in the youngest (16-31 years; n=151) and oldest (55-88 years; n=157) quartile of 629 adult outpatients who had taken LEV. We also analyzed the frequency of adverse effects leading to dose change or discontinuation ("intolerability") and specific adverse effects in the younger versus older adults. One-year retention was determined for younger and older adults newly started on LEV at our center. RESULTS Mean LEV CL differed significantly between older (46.5 ml/h/kg) and younger adults (78.3 ml/h/kg). On average, older patients had a 40% lower LEV CL than younger patients. Comedication with an enzyme-inducing antiepileptic drug (EIAED; mostly carbamazepine) was associated with a 24% higher clearance of LEV compared to those who were not on EIAEDs. This difference was 37% in a subgroup of patients whose LEV CL was compared while they were on and off EIAEDs. Stepwise linear regression identified younger age and comedication with an EIAED as significant predictors of increased LEV CL. A total of 34.3% of the 629 patients (31.7% of younger vs. 40.7% of older patients; p=0.16) reported intolerability to LEV on at least one occasion. This difference in tolerability reached significance in the group of patients newly started on LEV (26.3% vs. 41.0%; p=0.017). Drowsiness and psychiatric/behavioral side effects were the most common adverse effects associated with LEV use in both age groups. One-year retention was 72% in the older group vs. 54% in the younger group (not significant). CONCLUSION Older adults have lower CL than younger adults and require a mean 40% lower dose of LEV to achieve the same serum level. Comedication with an EIAED increases LEV CL by 24-37%. Younger adults tolerate LEV better than older adults, but 1-year retention was (nonsignificantly) higher in the older group.
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Affiliation(s)
- Lawrence J Hirsch
- Comprehensive Epilepsy Center, Department of Neurology, Neurological Institute, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA.
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173
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Klotz U. The role of pharmacogenetics in the metabolism of antiepileptic drugs: pharmacokinetic and therapeutic implications. Clin Pharmacokinet 2007; 46:271-9. [PMID: 17375979 DOI: 10.2165/00003088-200746040-00001] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Several different factors, including pharmacogenetics, contribute to interindividual variability in drug response. Like most other agents, many antiepileptic drugs (AEDs) are metabolised by a variety of enzymatic reactions, and the cytochrome P450 (CYP) superfamily has attracted considerable attention. Some of those CYPs exist in the form of genetic (allelic) variants, which may also affect the plasma concentrations or drug exposure (area under the plasma concentration-time curve [AUC]) of AEDs. With regard to the metabolism of AEDs, the polymorphic CYP2C9 and CYP2C19 are of interest. This review summarises the evidence as to whether such polymorphisms affect the clinical action of AEDs. In the case of mephenytoin, defects in its metabolism may be attributable to >10 mutated alleles (designated as *2, *3 and others) of the gene expressing CYP2C19. Consequently, poor metabolisers (PMs) and extensive metabolisers (EMs) could be differentiated, whose frequencies vary among ethnic populations. CYP2C19 contributes to the metabolism of diazepam and phenytoin, the latter drug also representing a substrate of CYP2C9, with its predominant variants being defined as *2 and *3. For both AEDs, there is maximally a 2-fold difference in the hepatic elimination rate (e.g. clearance) or the AUC between the extremes of EMs and PMs which, in the case of phenytoin (an AED with a narrow 'therapeutic window'), would suggest a dosage reduction only for patients who are carriers of mutated alleles of both CYP2C19 and CYP2C9, a subgroup that is very rare among Caucasians (about 1% of the population) but more frequent in Asians (about 10%). The minor contribution of CYP2C19 to the metabolism of phenobarbital (phenobarbitone) can be overlooked. In rare cases, valproic acid can be metabolised to the reactive (hepatotoxic) metabolite, 4-ene-valproic acid. It is not yet clear whether genetic variants of the involved enzyme (CYP2C9) are responsible for this problem. Likewise, the active metabolite of carbamazepine, carbamazepine-10,11-epoxide, is transformed by the microsomal epoxide hydrolase, an enzyme that is also highly polymorphic, but the pharmacokinetic and clinical consequences still need to be evaluated. Pharmacogenetic investigations have increased our general knowledge of drug disposition and action. As for old and especially new AEDs the pharmacogenetic influence on their metabolism is not very striking, it is not surprising that there are no treatment guidelines taking pharmacogenetic data into account. Therefore, the traditional and validated therapeutic drug monitoring approach, representing a direct 'phenotype' assessment, still remains the method of choice when an individualised dosing regimen is anticipated. Nevertheless, pharmacogenetics and pharmacogenomics can offer some novel contributions when attempts are made to maximise drug efficacy and enhance drug safety.
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Affiliation(s)
- Ulrich Klotz
- Dr Margarete Fischer-Bosch Institut für Klinische Pharmakologie, Stuttgart, Germany.
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174
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Landmark CJ, Rytter E, Johannessen SI. Clinical use of antiepileptic drugs at a referral centre for epilepsy. Seizure 2007; 16:356-64. [PMID: 17420145 DOI: 10.1016/j.seizure.2007.02.006] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2006] [Revised: 02/01/2007] [Accepted: 02/20/2007] [Indexed: 11/18/2022] Open
Abstract
PURPOSE The National Centre for Epilepsy in Norway admits patients with refractory epilepsy from the whole country. The purpose of this study was to investigate how antiepileptic drugs (AEDs) are used at the centre and compare it with the total consumption in the country and international guidelines regarding clinical use of AEDs. MATERIAL AND METHODS A prevalence study was carried out from patient records from 264 patients (136 adults and 128 children). The use of AEDs, gender, polytherapy, common drug combinations, serum concentration measurements, concomitant medication and comorbid conditions were investigated. RESULTS Of the 15 AEDs in use, valproate, lamotrigine and levetiracetam were most frequently used. In the country at large, carbamazepine, valproate and lamotrigine were used the most. Valproate and lamotrigine occurred most frequently in combination. In adults, oxcarbazepine and topiramate were used more frequently in women than in men. Children used benzodiazepines three times as often as adults. Newer AEDs were mostly used for partial seizures, in accordance with international guidelines. Thirty-five percent of adults and 20% of children suffered from comorbid CNS-related conditions. The use of concomitant medication was widespread. Serum concentrations were in accordance to recommended therapeutic ranges. CONCLUSION The results demonstrate that newer AEDs were much more frequently used at the epilepsy centre than in the country as a whole. The use of polytherapy was common, and therapeutic drug monitoring was used for optimal individualized drug treatment. AEDs were used in accordance to international guidelines and recommendations, which can serve as a reference for other prescribers.
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Affiliation(s)
- Cecilie Johannessen Landmark
- Department of Pharmacy, Faculty of Health Sciences, Oslo University College, Pilestredet 52, N-0167 Oslo, Norway.
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175
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Fehr C, Hohmann N, Gründer G, Dielentheis TF, Buchholz HG, Chechko N, Yakushev I, Landvogt C, Bartenstein P, Urban R, Schreckenberger M. Tiagabine does not attenuate alcohol-induced activation of the human reward system. Psychopharmacology (Berl) 2007; 191:975-83. [PMID: 17265078 DOI: 10.1007/s00213-006-0696-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/01/2006] [Accepted: 12/26/2006] [Indexed: 10/23/2022]
Abstract
RATIONALE The rewarding effects of ethanol and other drugs of abuse are mediated by activation of the mesolimbic dopamine system. Recent neuroimaging studies in primates and humans suggest that cocaine-induced dopamine stimulation might be diminished by drugs augmenting gamma-aminobutyric acid A (GABA-A) receptor function such as the GABA transaminase inhibitor vigabatrin. OBJECTIVES The objective of this study was to test the property of the selective GABA transporter 1 (GAT1) inhibitor tiagabine to block ethanol-induced activation of the mesolimbic reward system in an i.v. ethanol challenge. MATERIALS AND METHODS Twenty nonaddicted healthy volunteers underwent an i.v. ethanol challenge after 1 week of tiagabine (15 mg/day) administration. Neuronal activation was measured using [(18)F]-fluoro-deoxyglucose positron emission tomography (PET). RESULTS Tiagabine did not prevent ethanol-induced stimulation of the mesolimbic reward system but augmented ethanol-induced hypometabolism within areas of the visual system and the cerebellum. Tiagabine alone also decreased neuronal metabolism within parts of the right temporal cortex that are highly enriched with GABA-ergic neurons. CONCLUSIONS Our ethanol challenge imaging study does not provide supporting evidence that the GAT1 inhibitor tiagabine diminishes the rewarding effects of ethanol. Further PET imaging studies using established anticraving compounds, such as the mu-opioid receptor antagonist naltrexone and antiepileptic drugs affecting the GABA-ergic system more broadly, will provide additional important insights on the interaction between the GABA-ergic and the brain reward system in vivo and the suitability of GABA-ergic drugs as anticraving compounds.
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Affiliation(s)
- Christoph Fehr
- Department of Psychiatry, University of Mainz, Untere Zahlbacher Strasse 8, 55131, Mainz, Germany.
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176
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Volk HA, Matiasek LA, Luján Feliu-Pascual A, Platt SR, Chandler KE. The efficacy and tolerability of levetiracetam in pharmacoresistant epileptic dogs. Vet J 2007; 176:310-9. [PMID: 17468024 DOI: 10.1016/j.tvjl.2007.03.002] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2007] [Revised: 02/21/2007] [Accepted: 03/08/2007] [Indexed: 11/18/2022]
Abstract
Twenty-two dogs with idiopathic epilepsy which were pharmacoresistant to phenobarbitone and bromide were treated with levetiracetam as an add-on medication. Records of eight dogs were used retrospectively to determine a safe, efficient levetiracetam dosage. Fourteen dogs were entered into a prospective, open label, non-comparative study. After 2 months of levetiracetam oral treatment (10 mg/kg TID), 8/14 dogs responded significantly to the treatment and seizure frequency was reduced by 50%. In dogs that remained refractory, the dosage was increased to 20 mg/kg TID for 2 months. One further dog responded to levetiracetam treatment. Levetiracetam responders had a significant decrease in seizure frequency of 77% (7.9+/-5.2 to 1.8+/-1.7 seizures/month) and a decrease in seizure days per month of 68% (3.8+/-1.7 to 1.2+/-1.1 seizure days/month). However, 6/9 responders experienced an increase in seizure frequency and seizure days after 4-8 months continuing with the levetiracetam treatment at the last effective dosage. Levetiracetam was well tolerated by all dogs and sedation was the only side-effect reported in just one of the 14 dogs.
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Affiliation(s)
- Holger A Volk
- Department of Veterinary Clinical Sciences, Neurology, Royal Veterinary College, Hatfield, UK.
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177
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Dasgupta A. Usefulness of monitoring free (unbound) concentrations of therapeutic drugs in patient management. Clin Chim Acta 2007; 377:1-13. [PMID: 17026974 DOI: 10.1016/j.cca.2006.08.026] [Citation(s) in RCA: 113] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2006] [Revised: 08/11/2006] [Accepted: 08/24/2006] [Indexed: 11/28/2022]
Abstract
Drugs are bound to various serum proteins in different degrees and only unbound or free drug is pharmacologically active. Although free drug concentration can be estimated from total concentration, for strongly bound drugs, prediction of free level is not always possible. Conditions like uremia, liver disease and hypoalbuminemia can lead to significant increases in free drug resulting in drug toxicity even if the concentration of total drug is within therapeutic range. Drug-drug interactions may also lead to a disproportionate increase in free drug concentrations. Elderly patients may have increased free drug concentrations due to hypoalbuminemia. Elevated free phenytoin concentrations have also been reported in patients with AIDS and pregnancy. Currently free drug concentrations of anticonvulsants such as phenytoin, carbamazepine and valproic acid are widely measured in clinical laboratories. Newer drugs such as mycophenolic acid mofetil and certain protease inhibitors are also considered as candidates for monitoring free drug concentration.
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Affiliation(s)
- Amitava Dasgupta
- Department of Pathology and Laboratory Medicine, University of Texas-Houston Medical School, 6431 Fannin, MSB 2.292, Houston, TX 77030, United States.
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178
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Abstract
As in all patient populations, epilepsy is common in pregnant women. Consequently, approximately 1 in 200 pregnancies is exposed to antiepileptic drugs (AEDs). Although exposure to AEDs in utero has been associated with an increased risk of major fetal malformations, most women with epilepsy require medication throughout pregnancy, since seizures themselves may be potentially harmful not only for the mother but also for the developing fetus. Physiological changes during pregnancy result in a reduction in the serum concentrations of most AEDs, particularly in late pregnancy. Changes in protein binding lead to a greater reduction in total than free (active) drug concentrations. Pharmacokinetic changes in pregnancy show interindividual variability and are not well understood for most newer AEDs. However, recent studies have shown that changes in lamotrigine clearance are particularly marked, with increases in each trimester and a significant fall in plasma concentrations, leading to consequent breakthrough seizures in some women. Concentrations may then rise precipitously after delivery, leading to symptoms of lamotrigine toxicity. Therapeutic drug monitoring could theoretically guide adjustment of AED dosage to achieve good seizure control while minimising fetal exposure, although there are several limitations to such monitoring. Firstly, there are wide interindividual variations in serum drug concentrations, with seizure control often correlating poorly with a given therapeutic range. Secondly, therapeutic ranges have not been well defined for newer AEDs and their measurement is often not always available. Thirdly, for highly protein-bound drugs, although measurement of free drug concentrations may more accurately reflect drug availability during pregnancy than total drug concentrations, assays for this are not always available and may be unreliable. Thus, it may be useful, prior to pregnancy, to establish the total and free drug concentrations required to achieve optimal seizure control in a given individual. Regular monitoring of AEDs has been advocated in each trimester and shortly after delivery, with adjustment of dosage to avoid seizure precipitation during pregnancy or symptoms of toxicity after birth. More frequent monitoring has been recommended for lamotrigine. However, aggressive drug monitoring of any AED has yet to be proven to be effective in improving seizure control or care. Furthermore, higher doses may be associated with a greater potential for teratogenicity and it is not yet known whether longer term adverse effects may be related to in utero exposure in the latter half of pregnancy. There is limited evidence about the relationship of maternal serum drug concentrations and teratogenicity. While there is a theoretical role for therapeutic drug monitoring in improving the risk-to-benefit ratio of AED therapy during pregnancy, there are many practical limitations. Future work is needed to clarify its role in improving seizure control during pregnancy and identifying serum drug concentrations that may be considered safe for fetal exposure.
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Affiliation(s)
- Naghme Adab
- Department of Neurological Science, The Walton Centre for Neurology and Neurosurgery, Fazakerley, Lower Lane, Liverpool, UK.
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179
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Patsalos PN, Ghattaura S, Ratnaraj N, Sander JW. In situ metabolism of levetiracetam in blood of patients with epilepsy. Epilepsia 2007; 47:1818-21. [PMID: 17116020 DOI: 10.1111/j.1528-1167.2006.00819.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
PURPOSE Although levetiracetam undergoes minimum metabolism, B-esterases have been identified in whole blood that are capable of metabolising levetiracetam. The present study was designed to ascertain any variability in levetiracetam blood concentrations that could be attributed to in situ metabolism and which could impact on the utility of such concentration measurements in guiding therapeutic management. METHODS Blood samples were collected from 40 patients that were prescribed levetiracetam. Sera (Groups 1 and 2) or whole blood (Groups 3 and 4) were compared. Paraoxan, an inhibitor of B-esterase activity, was added to samples assigned to Groups 2 and 4. Samples within each group were assigned to Time 0 (frozen within 30 min of sample collection), Time 2 days and Time 7 days (samples kept at ambient temperature for 2 and 7 days). RESULTS For serum samples, mean levetiracetam concentrations at Time 2 days and Time 7 days were indistinguishable from Time 0, regardless of whether B-esterase activity was inhibited on not. In contrast, for whole blood, in the absence of B-esterase inhibition, mean levetiracetam concentrations declined over time (11% and 29%; 2 and 7 days) compared to baseline values. In the presence of B-esterase inhibitor, mean levetiracetam concentrations at 2 days were indistinguishable from baseline values, although at 7 days values declined by 4%. CONCLUSIONS If therapeutic monitoring of levetiracetam is to be undertaken, serum should be the matrix of choice and that whole blood should be separated as soon as possible after patient sampling so as to minimize in situ levetiracetam metabolism which could result in spuriously low concentrations and substantial intrapatient variability.
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Affiliation(s)
- Philip N Patsalos
- Pharmacology and Therapeutics Unit, Department of Clinical and Experimental Epilepsy, Institute of Neurology, London, United Kingdom.
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180
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Ma CL, Jiao Z, Jie Y, Shi XJ. Isocratic Reversed-Phase HPLC for Simultaneous Separation and Determination of Seven Antiepileptic Drugs and Two of their Active Metabolites in Human Plasma. Chromatographia 2007. [DOI: 10.1365/s10337-006-0157-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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181
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Alves G, Figueiredo I, Castel-Branco M, Loureiro A, Fortuna A, Falcão A, Caramona M. Enantioselective HPLC-UV method for determination of eslicarbazepine acetate (BIA 2-093) and its metabolites in human plasma. Biomed Chromatogr 2007; 21:1127-34. [PMID: 17594694 DOI: 10.1002/bmc.858] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Eslicarbazepine acetate (BIA 2-093) is a novel central nervous system drug undergoing clinical phase III trials for epilepsy and phase II trials for bipolar disorder. A simple and reliable chiral reversed-phase HPLC-UV method was developed and validated for the simultaneous determination of eslicarbazepine acetate, oxcarbazepine, S-licarbazepine and R-licarbazepine in human plasma. The analytes and internal standard were extracted from plasma by a solid-phase extraction using Waters Oasis HLB cartridges. Chromatographic separation was achieved by isocratic elution with water-methanol (88:12, v/v), at a flow rate of 0.7 mL/min, on a LichroCART 250-4 ChiraDex (beta-cyclodextrin, 5 microm) column at 30 degrees C. All compounds were detected at 225 nm. Calibration curves were linear over the range 0.4-8 microg/mL for eslicarbazepine acetate and oxcarbazepine, and 0.4-80 microg/mL for each licarbazepine enantiomer. The overall intra- and interday precision and accuracy did not exceed 15%. Mean relative recoveries varied from 94.00 to 102.23% and the limit of quantification of the assay was 0.4 microg/mL for all compounds. This method seems to be a useful tool for clinical research and therapeutic drug monitoring of eslicarbazepine acetate and its metabolites S-licarbazepine, R-licarbazepine and oxcarbazepine.
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Affiliation(s)
- Gilberto Alves
- Laboratory of Pharmacology, Faculty of Pharmacy, Coimbra University, Coimbra, Portugal
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182
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Pigeolet E, Jacqmin P, Sargentini-Maier ML, Stockis A. Population Pharmacokinetics of??Levetiracetam in Japanese and??Western Adults. Clin Pharmacokinet 2007; 46:503-12. [PMID: 17518509 DOI: 10.2165/00003088-200746060-00004] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
OBJECTIVE To assess the population pharmacokinetics of levetiracetam, a second-generation antiepileptic drug, in adult Japanese and Western populations. METHODS Data were pooled from ten matched clinical trials conducted in Japan and in Europe and the USA, in which levetiracetam was administered orally to healthy subjects and subjects with epilepsy. Overall, 5408 plasma concentrations were available from 524 subjects in six clinical pharmacology studies and two confirmatory and two long-term safety studies of add-on treatment for partial epilepsy. A one-compartment open model with first-order absorption and elimination was fitted to the plasma concentrations using nonlinear mixed-effects modelling with first-order estimation. RESULTS Ethnicity had no statistically significant effect on the pharmacokinetics of levetiracetam in the presence of the other covariates. Bodyweight, sex, creatinine clearance and concomitant intake of enzyme inducers or valproic acid had a statistically significant effect on apparent plasma clearance of levetiracetam. Bodyweight, disease and valproic acid had a statistically significant effect on the volume of distribution. Levetiracetam exposure (the area under the plasma concentration-time curve over the 12-hour dosing interval at steady state) was 12% higher in females than in males. Decreasing bodyweight from 70 kg to 40 kg was predicted to increase exposure by 16%, while halving creatinine clearance was predicted to increase exposure by 10%. Enzyme inducers reduced exposure by 8%, while valproic acid resulted in a 23% increase in exposure. The latter effect was assumed to arise from the known association between valproic acid and increased body fat, since levetiracetam is negligibly metabolised by cytochrome P450 enzymes. CONCLUSIONS Population pharmacokinetic analysis points to the absence of ethnic differences in the pharmacokinetics of levetiracetam between Japanese and Western populations, other than those arising from bodyweight differences. Small, clinically non-relevant differences between individual demographic characteristics suggest that dose adjustment is usually not necessary.
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183
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Pietrzak B, Czarnecka E. Effect of the administration of tiagabine and gabapentin on rabbit electroencephalogram activity. J Pharm Pharmacol 2006; 58:1367-72. [PMID: 17034660 DOI: 10.1211/jpp.58.10.0010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022]
Abstract
New generation antiepileptic drugs, including gabapentin and tiagabine, are used in monotherapy or in combination with other drugs for specific seizure types. The multidirectional mechanism of activity and varied pharmacological properties of these drugs suggest that they could also be used in the therapy of other diseases. A possible limitation of new generation antiepileptic drugs is the incidence of CNS-related adverse effects. Few studies have assessed the effect of new antiepileptic drugs on electroencephalogram (EEG) recordings in subjects using these drugs for diseases other than epilepsy. The aim of this study was to determine the effects of tiagabine and gabapentin on EEG recordings from the midbrain reticular formation, dorsal hippocampus and frontal cortex in rabbits. Tiagabine was administered orally at a single dose of 5 and 20 mg kg(-1), or repeatedly at a dose of 5 mg kg(-1) (twice a day) for 14 days. Gabapentin was administered orally at a single dose of 25 and 100 mg kg(-1), or repeatedly at a dose of 25 mg kg(-1) (twice a day) for 14 days. Both tiagabine and gabapentin caused changes indicative of CNS inhibitory properties, which may be associated with the adverse effects of the drugs. After repeated doses of the drugs, the changes in EEG recordings were less pronounced than after single doses, which may indicate adaptive changes. The hippocampus was found to be the least sensitive to the effect of gabapentin.
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Affiliation(s)
- Bogusława Pietrzak
- Department of Pharmacodynamics, Medical University of Łódź, Muszyńskiego 1, PL 90-151 Łódź, Poland.
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184
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Beck O, Ohman I, Nordgren HK. Determination of Lamotrigine and its Metabolites in Human Plasma by Liquid Chromatography-Mass Spectrometry. Ther Drug Monit 2006; 28:603-7. [PMID: 17038873 DOI: 10.1097/01.ftd.0000245779.64080.30] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
A method based on electrospray ionization liquid chromatography-mass spectrometry was developed for the quantitative determination of lamotrigine and three of its reported metabolites, lamotrigine-2-N-glucuronide, lamotrigine-2-N-methyl, and lamotrigine-2-N-oxide in human blood plasma. The method utilized sample preparation by precipitation of proteins with acetonitrile, chromatographic separation on a reversed-phase system by gradient elution, and monitoring of the protonated molecular ions. Two internal standards, 3,5-diamino-6-(2-methoxyphenyl)-1,2,4-triazine and morphine-3-glucuronide-D3, were utilized to achieve precise quantification. The method validation comprised a demonstration of an agreement in the quantification of lamotrigine with that of a routine HPLC-UV method. The limits of detection were between 0.05 and 0.16 micromol/L. The method was employed for the measurement of clinical samples collected from 55 patients in steady-state prior to the dose intake (trough level). Lamotrigine and the 2-N-glucuronide were typically detected, while the N-methyl and N-oxide metabolites were detected only rarely. The median lamotrigine plasma level was 24.0 micromol/L (range, 4.3 to 64 micromol/L), the median 2-N-glucuronide level was 2.4 micromol/L (range, <0.05 to 24 micromol/L), and the median lamotrigine 2-N-glucuronide/lamotrigine ratio was 0.11 (range, <0.01 to 0.64). In conclusion, this liquid chromatographic-mass spectrometric method is suitable for simultaneous determination of lamotrigine and its metabolites in human plasma.
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Affiliation(s)
- Olof Beck
- Department of Medicine, Division of Clinical Pharmacology, Karolinska University Hospital, Sweden.
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185
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Abstract
The number of medications used to treat different types of seizures has increased over the last 10-15 years. Most of the newer antiepileptic drugs (AEDs) are likely to be unfamiliar to many nephrologists. For both the older and newer AEDs, basic pharmacokinetic information, recommendations for drug dosing in patients with reduced kidney function or who are on dialysis, and adverse renal and fluid-electrolyte effects are reviewed. Newer AEDs are less likely to have significant drug-drug interactions than older agents, but are more likely to need dosage adjustment in patients with reduced kidney function. The most common renal toxicities of these drugs include metabolic acidosis, hyponatremia, and nephrolithiasis; interstitial nephritis and other adverse effects are less common. Little is known about the clearance of most of the newer AEDs with high-efficiency hemodialyzers or with peritoneal dialysis. Monitoring of drug levels when available, careful clinical assessment of patients taking AEDs, and close collaboration with neurologists is essential to the management of patients taking AEDs.
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Affiliation(s)
- Rubeen K Israni
- Renal-Electrolyte and Hypertension Division, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
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186
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Abstract
This article reviews anticonvulsant therapies in current use for dogs and cats and briefly describes new modes of anticonvulsant therapy that are being investigated or pending publication. Most of the information contained within the article is based on published information. Some of the information, however, is based on the author's clinical experience and is identified as such.
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Affiliation(s)
- Curtis W Dewey
- Department of Clinical Sciences, Cornell University, College of Veterinary Medicine, Ithaca, NY 14853, USA.
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187
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Eyal S, Lamb JG, Smith-Yockman M, Yagen B, Fibach E, Altschuler Y, White HS, Bialer M. The antiepileptic and anticancer agent, valproic acid, induces P-glycoprotein in human tumour cell lines and in rat liver. Br J Pharmacol 2006; 149:250-60. [PMID: 16894351 PMCID: PMC2014277 DOI: 10.1038/sj.bjp.0706830] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
BACKGROUND AND PURPOSE The antiepileptic drug valproic acid, a histone deacetylase (HDAC) inhibitor, is currently being tested as an anticancer agent. However, HDAC inhibitors may interact with anticancer drugs through induction of P-glycoprotein (P-gp, MDR1) expression. In this study we assessed whether valproic acid induces P-gp function in tumour cells. We also investigated effects of valproic acid on the mRNA for P-gp and the cytochrome P450, CYP3A, in rat livers. EXPERIMENTAL APPROACH Effects of valproic acid on P-gp were assessed in three tumour cell lines, SW620, KG1a and H4IIE. Accumulation of acetylated histone H3 in rats' livers treated for two or seven days with valproic acid was evaluated using a specific antibody. Hepatic expression of the P-gp genes, mdr1a, mdr1b and mdr2, was determined by real-time polymerase chain reaction. The effects of valproic acid on CYP3A were assessed by Northern blot analysis and CYP3A activity assays. KEY RESULTS Valproic acid (0.5-2.0 mM) induced P-gp expression and function up to 4-fold in vitro. The effect of a series of valproic acid derivatives on P-gp expression in SW620 and KG1a cells correlated with their HDAC inhibition potencies. Treatment of rats with 1 mmol kg(-1) valproic acid for two and seven days increased hepatic histone acetylation (1.3- and 3.5-fold, respectively) and the expression of mdr1a and mdr2 (2.2-4.1-fold). Valpromide (0.5-2.0 mM) did not increase histone acetylation or P-gp expression in rat livers, but induced CYP3A expression. CONCLUSIONS Valproic acid increased P-gp expression and function in human tumour cell lines and in rat liver. The clinical significance of this increase merits further investigation.
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Affiliation(s)
- S Eyal
- Department of Pharmaceutics, Faculty of Medicine, School of Pharmacy, The Hebrew University of Jerusalem Jerusalem, Israel
| | - J G Lamb
- Department of Pharmacology and Toxicology, University of Utah Salt Lake City, UT, USA
| | - M Smith-Yockman
- Department of Pharmacology and Toxicology, University of Utah Salt Lake City, UT, USA
| | - B Yagen
- Department of Medicinal Chemistry and Natural Products, Faculty of Medicine, School of Pharmacy, The Hebrew University of Jerusalem Jerusalem, Israel
- David R Bloom Center for Pharmacy, Faculty of Medicine, School of Pharmacy, The Hebrew University of Jerusalem Jerusalem, Israel
| | - E Fibach
- Department of Hematology, Hadassah-Hebrew University Medical Center Jerusalem, Israel
| | - Y Altschuler
- David R Bloom Center for Pharmacy, Faculty of Medicine, School of Pharmacy, The Hebrew University of Jerusalem Jerusalem, Israel
- Department of Pharmacology, Faculty of Medicine, School of Pharmacy, The Hebrew University of JerusalemIsrael
| | - H S White
- Department of Pharmacology and Toxicology, University of Utah Salt Lake City, UT, USA
| | - M Bialer
- Department of Pharmaceutics, Faculty of Medicine, School of Pharmacy, The Hebrew University of Jerusalem Jerusalem, Israel
- David R Bloom Center for Pharmacy, Faculty of Medicine, School of Pharmacy, The Hebrew University of Jerusalem Jerusalem, Israel
- Author for correspondence:
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188
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Almeida AM, Falcão AC, Sales F, Baldeiras I, Rocha MJ, Caramona MM. Lamotrigine pharmacokinetic evaluation in epileptic patients submitted to VEEG monitoring. Eur J Clin Pharmacol 2006; 62:737-42. [PMID: 16871388 DOI: 10.1007/s00228-006-0144-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2006] [Accepted: 05/08/2006] [Indexed: 11/25/2022]
Abstract
OBJECTIVE The aim of the present study was to evaluate the pharmacokinetic profile of lamotrigine (LTG) in epileptic patients submitted to video-electroencephalography (VEEG) monitoring and, in addition, to investigate the influence of concomitant antiepileptic drugs (AEDs) on the kinetics of LTG. METHODS The analysis assumed a one-compartment open model with first-order absorption and elimination. The kinetic estimates obtained in this population were validated by using the Prediction-Error approach. The influence of medication was also assessed by the calculation of the LTG concentration-to-dose ratio. Patients (n=135) were divided into four groups according to the co-medication: Group 1, patients taking LTG with enzyme-inducer agents; Group 2, patients receiving LTG with valproic acid; Group 3, patients receiving both inducers and inhibitors of LTG metabolism; Group 4, patients under AEDs not known to alter LTG metabolism. RESULTS The obtained estimates for clearance (CL) (L/h/kg) [0.075+/-0.029 (Group 1), 0.014+/-0.005 (Group 2), 0.025+/-0.008 (Group 3) and 0.044+/-0.011 (Group 4)] appear to be the most appropriate set to be implemented in clinical practice as prior information, as demonstrated by the accuracy and precision of the measurements. In addition, the influence of co-medication on the LTG profile was further confirmed by the basal LTG concentration-to-dose ratio. CONCLUSION The results of the present investigation may contribute to achieving the goal of optimizing patients' clinical outcomes by managing their medication regimen through measured drug concentrations. Patients submitted to VEEG monitoring may benefit from this study, as the results may be used to provide better drug management in this medical setting.
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Affiliation(s)
- A M Almeida
- Laboratory of Pharmacology, Faculty of Pharmacy, University of Coimbra, Largo D. Dinis, 3000-295 Coimbra, Portugal
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189
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Bondareva IB, Jelliffe RW, Gusev EI, Guekht AB, Melikyan EG, Belousov YB. Population pharmacokinetic modelling of carbamazepine in epileptic elderly patients: implications for dosage. J Clin Pharm Ther 2006; 31:211-21. [PMID: 16789986 DOI: 10.1111/j.1365-2710.2006.00717.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
BACKGROUND Proper use of antiepileptic drugs in the elderly involves knowledge of their pharmacokinetics to ensure a patient-specific balance between efficacy and toxicity. However, populations of epileptic patients on chronic carbamazepine (CBZ) therapy which have been studied have included data of relatively few elderly patients. AIMS The aim of the present study was to evaluate the population pharmacokinetics of CBZ in elderly patients on chronic monotherapy. METHODS We have used the non-parametric expectation maximization (NPEM) program in the USC*PACK collection of PC programs to estimate individual and population post-induction pharmacokinetics of CBZ in epileptic elderly patients who received chronic CBZ monotherapy. Age-related changes of CBZ population pharmacokinetics were evaluated from routine therapeutic drug monitoring (TDM) data of 37 elderly and 35 younger patients with epilepsy. As a 'historical control' we used previously published population modelling results from 99 young epileptic patients on chronic CBZ monotherapy. In that control group, TDM was performed in the same pharmacokinetic (PK) laboratory, using the same sampling strategy as in the present study, and the same PK population modelling software was used for data analysis. RESULTS AND CONCLUSIONS A poor correlation was found between daily CBZ dose and serum concentrations in the elderly patients (r=0.2, P=0.25). Probably statistically significant difference in the median values of the CBZ metabolic rate constant (P<0.001) between elderly and relatively young epileptic patients was found. Our results showed that age-related influences in CBZ pharmacokinetics in elderly patients should be considered in the optimal planning of CBZ dosage regimens. Most elderly patients with epilepsy will usually need CBZ dosages lower than those based on the median population PK parameter values obtained from younger patients. The present population model is also uniquely well suited for the new 'multiple model' design of dosage regimens to hit target therapeutic goals with maximum precision.
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Affiliation(s)
- I B Bondareva
- Laboratory of Mathematical Modeling, The Research Institute of Physico-Chemical Medicine, Moscow, Russia.
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190
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Jann MW, Hon YY, Shamsi SA, Zheng J, Awad EA, Spratlin V. Lack of Pharmacokinetic Interaction Between Lamotrigine and Olanzapine in Healthy Volunteers. Pharmacotherapy 2006; 26:627-33. [PMID: 16637792 DOI: 10.1592/phco.26.5.627] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
STUDY OBJECTIVE To investigate the potential drug-drug interaction between lamotrigine, an antiepileptic agent used to treat bipolar disorders, and olanzapine, an atypical antipsychotic drug also used to treat bipolar disorders, both of which are metabolized by the uridine diphosphate glucuronosyltransferase system. DESIGN Prospective cohort study. SETTING University center for clinical research. SUBJECTS Fourteen nonsmoking, healthy volunteers. INTERVENTION Subjects received lamotrigine 25 mg/day for 5 days, then 50 mg/day for 10 days to achieve steady-state concentrations. On day 15, blood samples were obtained before and 0.5, 1, 2, 3, 4, 6, 8, 10, 12, and 24 hours after the dose. Lamotrigine 50 mg/day was then given for an additional 3 days. On the next day, lamotrigine 50 mg and olanzapine 5 mg were coadministered. Blood samples were obtained at the same times as before and at 48, 72, and 96 hours after dosing. MEASUREMENTS AND MAIN RESULTS Blood samples were assayed for lamotrigine and olanzapine concentrations by means of high-performance liquid chromatography. Olanzapine did not significantly affect lamotrigine disposition, as we observed no differences in the area under the concentration-time curve from 0-24 hours or in lamotrigine plasma concentrations at baseline or at 24 hours. For lamotrigine, the mean time to reach maximum concentration was significantly prolonged during olanzapine coadministration (mean +/- SD 1.9 +/- 1.3 vs 4.0 +/- 3.0 hrs, p = 0.025), possibly because of the anticholinergic properties associated with olanzapine. Mild sedation was the only adverse effect that occurred during lamotrigine and olanzapine coadministration. CONCLUSION Lamotrigine and olanzapine can safely be combined in healthy volunteers at the low doses studied, without a clinically significant interaction. When prescribing high doses of olanzapine and lamotrigine for bipolar disorder, patients must be carefully monitored.
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Affiliation(s)
- Michael W Jann
- Department of Clinical and Administrative Sciences, Mercer University, Southern School of Pharmacy, Atlanta, Georgia 30341, USA
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191
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Clarke W, McMillin G. Application of TDM, pharmacogenomics and biomarkers for neurological disease pharmacotherapy: focus on antiepileptic drugs. Per Med 2006; 3:139-149. [PMID: 29793289 DOI: 10.2217/17410541.3.2.139] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Anticonvulsants, or antiepileptic drugs (AEDs), are a vital tool in the therapeutic management of epilepsy patients. However, many AEDs are commonly used in the management of nonepileptic conditions, such as chronic pain, migraine headaches and psychiatric disorders. It is well documented that serum drug levels are an important data tool for the management of patients taking these drugs. As we move toward the personalized optimization of pharmacotherapy, drug level data will not be sufficient. This article will review tools for therapeutic drug management of AEDs including pharmacogenetics and biomarkers, in addition to traditional serum drug levels.
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Affiliation(s)
- William Clarke
- Johns Hopkins School of Medicine, Department of Pathology, Baltimore, MD, 21287, USA.
| | - Gwen McMillin
- University of Utah, ARUP Institute for Clinical and Experimental Pathology, Department of Pathology, Salt Lake City, UT, 84108, USA.
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192
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Striano S, Striano P, Di Nocera P, Italiano D, Fasiello C, Ruosi P, Bilo L, Pisani F. Relationship between serum mono-hydroxy-carbazepine concentrations and adverse effects in patients with epilepsy on high-dose oxcarbazepine therapy. Epilepsy Res 2006; 69:170-6. [PMID: 16515857 DOI: 10.1016/j.eplepsyres.2006.01.011] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2005] [Revised: 01/17/2006] [Accepted: 01/25/2006] [Indexed: 11/18/2022]
Abstract
PURPOSE To investigate the relationship between the serum concentration of the mono-hydroxy-derivative (MHD) of oxcarbazepine (OXC) and adverse effects (AEs) in epileptic patients on high-dose OXC therapy. PATIENTS AND METHODS Forty-four consecutive patients, aged 18-65 years, with refractory epilepsy receiving OXC dosages > or = 1500 mg/day (range 1500-3300 mg/day) were assessed at an outpatient clinic. Serum MHD concentrations were determined by a specific HPLC assay in samples collected before the morning dose and 2 h after drug intake. An independent observer assessed AEs at each sampling time. RESULTS AEs were reported in five patients at the first sampling time, and in 26 patients at the second sampling time. Nystagmus, sedation, blurred vision, and dizziness were the most frequent AEs. MHD concentrations (means +/- S.D.) associated with AEs were 29.6 +/- 5.58 compared with 21.7 +/- 5.0 mg/L when no AEs were detected (p = 0.0001). AEs were minimized in most patients by reducing OXC dose, increasing the number of daily administrations, or both. CONCLUSION Patients with serum MHD concentrations > or = 30 mg/L are at greater risk of developing AEs. In many patients, AEs occur intermittently in relation to fluctuations in serum MHD. Monitoring MHD concentrations could help in the management of patients on high-dose OXC therapy.
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Affiliation(s)
- Salvatore Striano
- Epilepsy Center, Department of Neurological Sciences, Federico II University, Naples, Italy.
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193
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Fulton JA, Hoffman RS, Nelson LS. Tiagabine overdose: a case of status epilepticus in a non-epileptic patient. Clin Toxicol (Phila) 2006; 43:869-71. [PMID: 16440516 DOI: 10.1080/15563650500357586] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Tiagabine is an antiepileptic drug used as adjunctive therapy for partial seizures that is believed to selectively inhibit the presynaptic reuptake of gamma aminobutyric acid (GABA). We describe a case of a tiagabine overdose that resulted in status epilepticus (SE) in a patient with no seizure history. A 14-year-old girl with a history of asthma presented with convulsive SE after ingestion of an unknown amount of her sister's tiagabine in a suicide attempt. Attempted anticonvulsant therapy included a total of diazepam 10 mg IV, lorazepam 6 mg IV, pyridoxine 5 g IV, and fosphenytoin 20 mg PE/kg. All were without effect. A computed tomography and electrocardiogram were normal. Continuous bedside EEG monitoring showed suppression of seizure activity following intravenous midazolam. A tiagabine level obtained on ED arrival was 420 ng/mL (therapeutic 20-103 ng/mL). The patient was discharged to psychiatry within 1 week with no neurologic sequelae.
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194
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Abstract
In recent years, several new-generation antiepileptic drugs (AEDs) have been introduced in clinical practice. These agents, which include felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, tiagabine, topiramate, vigabatrin and zonisamide, are being increasingly used in the treatment of epilepsy at the extremes of age. For a rational prescribing of these drugs in specific age groups, major pharmacokinetic changes that occur during development and aging need to be taken into consideration. A review of available evidence indicates that the apparent oral clearance (CL/F) of new-generation AEDs in children is increased by 20-170% (depending on the type of drug and characteristics of the patients studied) compared with adults, with the highest CL/F values usually being observed in the youngest age groups. These findings do not necessarily apply to the first weeks of life, when drug eliminating capacity is still undergoing maturation, as in the case of lamotrigine for which preliminary data suggest that CL/F in neonates aged <2 months can be much lower than in infants aged 2-12 months. At the other extreme of age, in the elderly, CL/F is almost invariably reduced (on average by 10-50%) compared with values found in non-elderly adults. Age-related CL/F changes, together with the large interindividual pharmacokinetic variability, contribute to the need for individualised dosage requirements in these patients. Measurement of serum drug concentrations can be useful as an aid to dosage individualization in these age groups but interpretation of therapeutic drug monitoring data should also take into account the possibility of age-related changes in pharmacodynamic sensitivity and, for neonates and the elderly, alterations in drug binding to serum proteins.
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Affiliation(s)
- Emilio Perucca
- Clinical Pharmacology Unit, Department of Internal Medicine and Therapeutics, University of Pavia, Pavia, Italy.
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195
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Abstract
A new generation of antiepileptic drugs (AEDs) has reached the market in recent years with ten new compounds: felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, tiagabine, topiramate, vigabatrin and zonisamide. The newer AEDs in general have more predictable pharmacokinetics than older AEDs such as phenytoin, carbamazepine and valproic acid (valproate sodium), which have a pronounced inter-individual variability in their pharmacokinetics and a narrow therapeutic range. For these older drugs it has been common practice to adjust the dosage to achieve a serum drug concentration within a predefined 'therapeutic range', representing an interval where most patients are expected to show an optimal response. However, such ranges must be interpreted with caution, since many patients are optimally treated when they have serum concentrations below or above the suggested range. It is often said that there is less need for therapeutic drug monitoring (TDM) with the newer AEDs, although this is partially based on the lack of documented correlation between serum concentration and drug effects. Nevertheless, TDM may be useful despite the shortcomings of existing therapeutic ranges, by utilisation of the concept of 'individual reference concentrations' based on intra-individual comparisons of drug serum concentrations. With this concept, TDM may be indicated regardless of the existence or lack of a well-defined therapeutic range. The ten newer AEDs all have different pharmacological properties, and therefore, the usefulness of TDM for these drugs has to be assessed individually. For vigabatrin, a clear relationship between drug concentration and clinical effect cannot be expected because of its unique mode of action. Therefore, TDM of vigabatrin is mainly to check compliance. The mode of action of the other new AEDs would not preclude the applicability of TDM. For the prodrug oxcarbazepine, TDM is also useful, since the active metabolite licarbazepine is measured. For drugs that are eliminated renally completely unchanged (gabapentin, pregabalin and vigabatrin) or mainly unchanged (levetiracetam and topiramate), the pharmacokinetic variability is less pronounced and more predictable. However, the dose-dependent absorption of gabapentin increases its pharmacokinetic variability. Drug interactions can affect topiramate concentrations markedly, and individual factors such as age, pregnancy and renal function will contribute to the pharmacokinetic variability of all renally eliminated AEDs. For those of the newer AEDs that are metabolised (felbamate, lamotrigine, oxcarbazepine, tiagabine and zonisamide), pharmacokinetic variability is just as relevant as for many of the older AEDs. Therefore, TDM is likely to be useful in many clinical settings for the newer AEDs. The purpose of the present review is to discuss individually the potential value of TDM of these newer AEDs, with emphasis on pharmacokinetic variability.
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196
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Pippenger CE. Therapeutic drug monitoring assay development to improve efficacy and safety. Epilepsy Res 2006; 68:60-3. [PMID: 16377149 DOI: 10.1016/j.eplepsyres.2005.09.022] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2005] [Accepted: 09/14/2005] [Indexed: 10/25/2022]
Abstract
The development of therapeutic drug management (TDM) utilizing diagnostic assays as biomarker tests is described. TDM can be useful in establishing an individual patient's optimal blood concentration range, and benchmarking blood concentrations at which seizures are controlled, as well as those associated with AED-specific adverse effects. TDM requires the application of pharmacokinetic, pharmacodynamic, pharmacogenomic, pathophysiological and clinical principles to the management of patients in order to achieve safe and effective therapy. Optimal therapy requires rational application of all these principles to personalize patient care.
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197
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Ji HY, Jeong DW, Kim YH, Kim HH, Yoon YS, Lee KC, Lee HS. Determination of gabapentin in human plasma using hydrophilic interaction liquid chromatography with tandem mass spectrometry. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2006; 20:2127-32. [PMID: 16773671 DOI: 10.1002/rcm.2573] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
A rapid, sensitive and selective method for the determination of gabapentin in human plasma was developed using hydrophilic interaction liquid chromatography/tandem mass spectrometry (HILIC/MS/MS). The devised method involved protein precipitation with acetonitrile followed by separation on an Atlantis HILIC silica column using an acetonitrile/ammonium formate mobile phase (100 mM, pH 3.0) (85:15, v/v). Analytes were detected using an electrospray ionization mass spectrometer in the multiple-reaction monitoring mode. The standard curve was linear (r = 1.000) over the concentration range of 50.0-10000 ng/mL. The lower limit of quantification for gabapentin was 50.0 ng/mL (ca. 20 pg gabapentin) using a 10-microL plasma sample. The coefficients of variation and relative errors for intra- and inter-assay at four QC levels (i.e., 50.0, 125, 750, and 7500 ng/mL) were 4.7 to 9.4% and -4.1 to 1.6%, respectively. Absolute and relative matrix effects for gabapentin and metformin were practically absent. Gabapentin and metformin recoveries were 98.5% and 99.0%, respectively. This method was successfully applied to a bioequivalence study of gabapentin in humans.
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Affiliation(s)
- Hye Young Ji
- Drug Metabolism and Bioanalysis Laboratory, College of Pharmacy and Phytofermentation Research Center, Wonkwang University, Iksan 570-749, Korea
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Abstract
Focal-onset seizures are manifestations of abnormal epileptic firing of brain cells in a localised area or areas of the brain. The diagnosis of focal-onset seizures initially entails an EEG, a detailed history from the patient and eyewitnesses, as well as computer tomographic or, preferably, magnetic resonance imaging scans. Video EEG to record ictal events may be necessary to establish the correct diagnosis. Focal seizures are classified according to the International Classification of Epileptic Seizures and International Classification of Epilepsies and Epilepsy Syndromes. It is important to try to decide how the seizure event fits into this system in order to successfully evaluate and optimise treatment, as well as to give detailed information to the patient about their seizures and prognosis. Once the decision to treat the seizures has been made, the physician must choose which medication is the most appropriate to begin with. Carbamazepine, phenytoin or valproic acid (sodium valproate) are often rated as first-line drugs, but factors such as adverse-effect profiles, age, possibility of pregnancy, and concomitant diseases and medication also need to be considered. Most of the newer antiepileptic drugs (AEDs) appear to have good efficacy and better tolerability than the older agents, but evidence to support their superiority is scarce and has led to conflicting advice in several guidelines. Among the newer AEDs, lamotrigine, gabapentin, topiramate and oxcarbazepine have obtained monotherapy indication in many countries. The higher costs of the newer AEDs may inhibit their wider use, especially in poorer countries.
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199
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Okada M, Yoshida S, Zhu G, Hirose S, Kaneko S. Biphasic actions of topiramate on monoamine exocytosis associated with both soluble N-ethylmaleimide-sensitive factor attachment protein receptors and Ca(2+)-induced Ca(2+)-releasing systems. Neuroscience 2005; 134:233-46. [PMID: 15961239 DOI: 10.1016/j.neuroscience.2005.03.045] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2005] [Revised: 03/26/2005] [Accepted: 03/30/2005] [Indexed: 11/25/2022]
Abstract
To explore the pharmacological mechanisms of topiramate (TPM), we determined the effects of TPM on monoamine (dopamine and serotonin) exocytosis associated with N-ethylmaleimide-sensitive factor attachment protein receptors and Ca(2+)-induced Ca(2+)-releasing systems, including inositol-triphosphate receptor and ryanodine receptor in freely moving rat pre-frontal cortex using in vivo microdialysis. During resting stage, Ca(2+) output from endoplasmic reticulum Ca(2+) store via inositol-triphosphate receptor regulates syntaxin-associated monoamine exocytosis mechanism, whereas during neuronal hyperexcitable stage, Ca(2+) output via ryanodine receptor regulates synaptobrevin-associated monoamine exocytosis mechanism. Basal monoamine releases were increased and decreased by therapeutically relevant and supratherapeutic concentration of TPM, respectively. The therapeutic-relevant concentration of TPM increased Ca(2+)-evoked release concentration-dependently; however, its stimulatory effect was attenuated in the supratherapeutic range. The K(+)-evoked releases were reduced by TPM concentration-dependently (from therapeutic to supratherapeutic ranges). The therapeutic-relevant concentration of TPM-induced elevation of basal release was reduced by cleavage with syntaxin and inhibition of inositol-triphosphate receptor predominantly, by cleavage with SNAP-25 and synaptobrevin weakly, but not by ryanodine receptor inhibitor. The therapeutic-relevant concentration of TPM-induced elevation of Ca(2+)-evoked release was reduced by cleavage with syntaxin and inositol-triphosphate receptor inhibitor selectively. The therapeutic-relevant concentration of TPM-induced reduction of K(+)-evoked monoamine release was abolished by cleavage with synaptobrevin, but was not affected by cleavage with SNAP-25 or synaptobrevin. The stimulatory effect of ryanodine receptor agonist on K(+)-evoked monoamine release was reduced by TPM, whereas that of inositol-triphosphate receptor agonist was not affected by TPM. Therefore, these results indicate that the combination of the effects of TPM on exocytosis mechanisms associated with SNARE and Ca(2+)-induced Ca(2+)-releasing systems, enhancement of inositol-triphosphate receptor/syntaxin and inhibition of ryanodine receptor/synaptobrevin in pre-frontal cortex, may be involved in clinical actions of TPM.
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Affiliation(s)
- M Okada
- Department of Neuropsychiatry, School of Medicine, Hirosaki University, Hirosaki 036-8562, Japan.
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200
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Abstract
The aim of this brief communication is to update our recent review on therapeutic drug monitoring (TDM) of the newer antiepileptic drugs (AEDs). The potential value of TDM is discussed in relation to their mode of action and their pharmacokinetic proper-ties. Data on the relationships between serum concentrations and clinical efficacy are limited, and few studies have been designed primarily to study these relationships. As yet there are no generally accepted target ranges for any of the new AEDs. For most drugs a wide range in serum concentration is associated with clinical efficacy,and there is a considerable overlap in serum concentrations related to toxicity and lack of clinical efficacy. Although the available documentation is clearly insufficient, the pharmacological properties of some of the drugs suggest that they may be suitable candidates for TDM. The primary role of TDM for both the newer and established AEDs is to identify an individual's optimum concentration and thus establish a reference value in that patient.
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