Levetiracetam Therapeutic Monitoring in Patients with Epilepsy

Clinical value of therapeutic drug monitoring for levetiracetam in pediatric patients with epilepsy

PURPOSE

To identify pediatric patients who require therapeutic drug monitoring (TDM) of levetiracetam (LEV).

METHODS

We retrospectively investigated 2413 routine therapeutic drug monitoring data on serum LEV concentration from 1398 pediatric patients (age, 0-15 years). Samples were grouped by age (infants, < 1 year; preschool children, 1-5 years; primary school children, 6-11 years; and adolescents, 12-15 years), and the LEV concentration-to-dose (CD) ratio was calculated.

RESULTS

The mean CD ratio was highest in adolescents (analysis of variance, p < 0.001); 22.5 % and 15.7 % higher in adolescents than in preschool children and school children, respectively (Scheffé test, p < 0.001); and higher in infants than in preschool children. Preschool children had the lowest ratio and tended to show an increase in the ratio from age 2 to 5 years. Use of enzyme-inducing antiseizure medication reduced the CD ratio by 6.1 % in infants, 12.2 % in preschool children, 5.9 % in primary school children, and 9.4 % in adolescents. The mean CD ratio was 2.7 %, 26.9 %, and 39.3 % higher in preschool children, primary school children, and adolescents with defined chronic kidney disease (CKD) than in the respective age group of patients without CKD. The therapeutic concentration range for a long-term LEV therapy was 11 to 32 μg/mL.

CONCLUSIONS

LEV pharmacokinetics are significantly different between infant and preschool children, so TDM of LEV is clinically useful in these patients. In pediatric patients at higher risk for CKD, glomerular filtration rate and LEV levels should be carefully monitored.

Cytochrome P450-mediated antiseizure medication interactions influence apoptosis, modulate the brain BAX/Bcl-XL ratio and aggravate mitochondrial stressors in human pharmacoresistant epilepsy

Polytherapy with antiseizure medications (ASMs) is often used to control seizures in patients suffering from epilepsy, where about 30% of patients are pharmacoresistant. While drug combinations are intended to be beneficial, the consequence of CYP-dependent drug interactions on apoptotic protein levels and mitochondrial function in the epileptic brain remains unclear. We examined the interactions of ASMs given prior to surgery in surgically resected brain tissues and of three ASMs (lacosamide, LCM; oxcarbazepine, OXC; levetiracetam LEV) in isolated brain cells from patients with drug-resistant epilepsy (n = 23). We divided the patients into groups-those who took combinations of NON-CYP + CYP substrate ASMs, NON-CYP + CYP inducer ASMs, CYP substrate + CYP substrate or CYP substrate + CYP inducer ASMs-to study the 1) pro- and anti-apoptotic protein levels and other apoptotic signaling proteins and levels of reactive oxygen species (reduced glutathione and lipid peroxidation) in brain tissues; 2) cytotoxicity at blood-brain barrier epileptic endothelial cells (EPI-ECs) and subsequent changes in mitochondrial membrane potential in normal neuronal cells, following treatment with LCM + OXC (CYP substrate + CYP inducer) or LCM + LEV (CYP substrate + NON-CYP-substrate) after blood-brain barrier penetration, and 3) apoptotic and mitochondrial protein targets in the cells, pre-and post-CYP3A4 inhibition by ketoconazole and drug treatments. We found an increased BAX (pro-apoptotic)/Bcl-XL (anti-apoptotic) protein ratio in epileptic brain tissue after treatment with CYP substrate + CYP substrate or inducer compared to NON-CYP + CYP substrate or inducer, and subsequently decreased glutathione and elevated lipid peroxidation levels. Further, increased cytotoxicity and Mito-ID levels, indicative of compromised mitochondrial membrane potential, were observed after treatment of LCM + OXC in combination compared to LCM + LEV or these ASMs alone in EPI-ECs, which was attenuated by pre-treatment of CYP inhibitor, ketoconazole. A combination of two CYP-mediated ASMs on EPI-ECs resulted in elevated caspase-3 and cytochrome c with decreased SIRT3 levels and activity, which was rescued by CYP inhibition. Together, the study highlights for the first time that pro- and anti-apoptotic proteins levels are dependent on ASM combinations in epilepsy, modulated via a CYP-mediated mechanism that controls free radicals, cytotoxicity and mitochondrial activity. These findings lead to a better understanding of future drug selection choices offsetting pharmacodynamic CYP-mediated interactions.

Levetiracetam Therapeutic Drug Monitoring in a Large Cohort of Korean Epileptic Patients

Levetiracetam is a new antiepileptic drug (AED) used for treating and preventing partial or generalized seizures. The usefulness of levetiracetam therapeutic drug monitoring (TDM) is related to inter- or intra-individual pharmacokinetic variability, drug interactions, and patient noncompliance. We aimed to investigate the levetiracetam TDM status in Korean epilepsy patients. Serum trough levetiracetam concentrations were measured using liquid chromatography–tandem mass spectrometry in 710 samples from 550 patients. The median (range) daily and weight-adjusted levetiracetam doses were 1500 (20–5000) mg and 25.5 (3.03–133.0) mg/kg, respectively. Patients on levetiracetam monotherapy constituted only 19.5% of the population, while 30.1% were on co-medication with valproate and 56.0% with enzyme-inducing AEDs (EIAEDs). Observed levetiracetam concentrations were widely distributed, ranging 0.8–95 mg/L, with a median of 17.3 mg/L. Levetiracetam concentrations were therapeutic, supra-therapeutic, and sub-therapeutic in 58.5% (n = 393), 11.6% (n = 78), and 29.9% (n = 201) of samples, respectively. There was a strong correlation between weight-adjusted levetiracetam dosage and concentrations (ρ = 0.6896, p < 0.0001). In this large-scale clinical study, a large inter-individual difference in levetiracetam pharmacokinetics was observed, and levetiracetam concentrations were influenced by EIAEDs. For individual dose adjustments and monitoring compliance, routine levetiracetam TDM is needed in epilepsy patients.

Which treatment strategy in patients with epilepsy with focal seizures uncontrolled by the first anti-seizure medication?

There is no definite proven or accepted strategy in the management of patients with focal epilepsy uncontrolled by the first anti-seizure medication (ASM). Clinical studies failed to find a significant difference in efficacy or tolerability between alternative monotherapy and/or adjunctive therapy in these patients. A second ASM is often added, the efficacy of the combination is assessed, and the dose of the first drug can be gradually reduced and withdrawn. If seizures recur, the effective combination therapy can be reinstated. In this review, we discussed experimental and clinical data about the efficacy and tolerability of the most frequently used combinations of ASMs. Animal studies suggested that the most favorable combinations are those between ASMs with different or multiple mechanisms of action, whereas combining drugs with similar pharmacodynamic properties is often associated with additive or infra-additive efficacy and additive or synergistic toxicity. Clinical studies have shown that levetiracetam (LEV) can be favorably combined with the sodium channel blockers (SCBs) lacosamide (LCM) and lamotrigine (LTG). Lamotrigine is particularly effective when associated with valproate (VPA) and possibly with LEV and topiramate (TPM). Carbamazepine (CBZ) has negative pharmacokinetic interactions with several ASMs and should not be combined with other SCBs; it could be effectively and safely combined with gabapentin (GBP) and LEV. Valproic acid has enzyme inhibiting properties and can be cautiously used with SCBs; its combination with TPM or zonisamide (ZNS) may be associated with higher toxicity.

Population Pharmacokinetics of Levetiracetam: a Systematic Review

BACKGROUND

The use of levetiracetam (LEV) has been increasing given its favorable pharmacokinetic profile. Numerous population pharmacokinetic studies for LEV have been conducted. However, there are some discrepancies regarding factors affecting its pharmacokinetic variability. Therefore, this systematic review aimed to summarize significant predictors for LEV pharmacokinetics as well as the need for dosage adjustments.

METHODS

We performed a systematic search for population pharmacokinetic studies of LEV conducted using a nonlinear-mixed effect approach from PubMed, Scopus, CINAHL Complete, and Science Direct databases from their inception to March 2020. Information on study design, model methodologies, significant covariate-parameter relationships, and model evaluation was extracted. The quality of the reported studies was also assessed.

RESULTS

A total of 16 studies were included in this review. Only two studies were conducted with a two-compartment model, while the rest were performed with a one-compartment structure. Bodyweight and creatinine clearance were the two most frequently identified covariates on LEV clearance (CLLEV). Additionally, postmenstrual age (PMA) or postnatal age (PNA) were significant predictors for CLLEV in neonates. Only three studies externally validated the models. Two studies conducted pharmacodynamic models for LEV with relatively small sample size.

CONCLUSION

Significant predictors for LEV pharmacokinetics are highlighted in this review. For future research, a population pharmacokinetic-pharmacodynamic model using a larger sample size should be conducted. From a clinical perspective, the published models should be externally evaluated before clinical implementation.

Pharmacokinetic Monitoring of Levetiracetam in Portuguese Refractory Epileptic Patients: Effect of Gender, Weight and Concomitant Therapy

Levetiracetam is a second-generation antiepileptic drug, widely used in the treatment of focal and generalized epilepsy due to its pharmacokinetic and safety profiles. Its pharmacokinetic monitoring is ascribed as useful to personalize its dosing regimen. The aim of the present study was to describe, for the first time, the pharmacokinetics of levetiracetam in Portuguese refractory epileptic patients. Therefore, a retrospective study was carried out on 65 Portuguese refractory epileptic patients (pharmacokinetic study: 48; validation study: 17) admitted to the Refractory Epilepsy Centre of the Centro Hospitalar e Universitário de Coimbra, Coimbra, Portugal. The pharmacokinetic parameters of levetiracetam were estimated by applying a one-compartment model with first-order absorption and elimination analysis. Male patients showed higher distribution volume (Vd/F) and oral clearance (CL/F) than female patients (median Vd/F: 52.40 L in males and 38.60 L in females, p = 0.011; median CL/F: 4.71 L/h in males and 3.91 L/h in females, p = 0.028). Higher values of Vd/F (p = 0.026) and CL/F (p = 0.003) were also found in overweight patients relative to normal weight and obese patients. Carbamazepine was the co-administered antiepileptic drug that mostly affected the pharmacokinetics of levetiracetam, increasing both Vd/F (61.30 L with carbamazepine and 39.10 L without carbamazepine, p = 0.007) and CL/F (6.71 L/h with carbamazepine and 3.91 L/h without carbamazepine, p < 0.001). The pharmacokinetics of levetiracetam was affected by gender, body mass index, and co-administration of carbamazepine. This study highlights the impact of several factors on the CL/ and Vd/F of levetiracetam when administered to refractory epileptic patients. The importance of its pharmacokinetic monitoring in clinical pharmacy stands out, thereby enabling the optimization of antiepileptic drug therapy.

Population Pharmacokinetic Modeling of Levetiracetam in Pediatric and Adult Patients With Epilepsy by Using Routinely Monitored Data

BACKGROUND

Levetiracetam, a second-generation antiepileptic drug, is frequently used for managing partial-onset seizures. About 70% of the administered dose is excreted in urine unchanged, and dosage adjustment is recommended based on the individual's renal function. In this study, a population pharmacokinetic model of levetiracetam was developed using routinely monitored serum concentration data for individualized levetiracetam therapy.

METHODS

Patients whose serum concentrations of levetiracetam at steady-state were routinely monitored at Kyoto University Hospital from April 2012 to March 2013 were enrolled. The influence of patient characteristics on levetiracetam pharmacokinetics was evaluated using the nonlinear mixed-effects modeling (NONMEM) program.

RESULTS

A total of 583 steady-state concentrations from 225 patients were used for the analysis. The median patient age and estimated glomerular filtration rate (eGFR) were 38 (range: 1-89) years and 98 (15-189) mL·min·1.73 m, respectively. Serum concentration-time data of levetiracetam were well described by a 1-compartment model with first-order absorption. Oral clearance was allometrically related to the individual body weight and eGFR. An increase in the dose significantly increased oral clearance. No improvement in model fit was observed by including the covariate of any concomitant antiepileptic drugs. The population mean clearance for an adult weighing 70 kg and with a normal renal function was 4.8 and 5.9 L/h for 500 mg bis in die (bid) and 1500 mg bid, respectively.

CONCLUSIONS

Oral clearance allometrically related with body weight and eGFR can well predict the routine therapeutic drug monitoring data from pediatric to aged patients with varying renal function. Dosage adjustments based on renal function are effective in controlling the trough and peak concentrations in similar ranges.

An Analytical Study to Correlate Serum Levels of Levetiracetam with Clinical Course in Patients with Epilepsy

Introduction:

With the advancement of therapeutics, newer antiepileptic drugs (AEDs) like Levetiracetam (LEV), with good therapeutic efficacy and tolerability are available. But unfortunately, therapeutic drug monitoring is not routinely done in India for these drugs.

Objectives:

The objective of this study is to determine the range of serum levels of LEV in patients at stabilized doses and correlate them with their clinical course.

Materials and Methods:

Patients with epilepsy and started on LEV were enrolled from the Neurology Department after the Ethics Committee approval. Serum levels of LEV were estimated using high-performance liquid chromatography and correlated with patient demographics, dosage, dosage forms, concomitant AEDs, compliance of the patient, therapeutic effect, adverse drug reactions (ADRs), and suspected toxicity.

Results:

Serum levels of LEV ranged from 0.4 to 102.2 μg/ml at different time points and demonstrated a negligible positive correlation with age of the patients (r = 0.12) but negligible negative correlation with bodyweight (r = −0.19). No conclusive relationship could be established for dose, gender, dosage forms, clinical efficacy (seizure frequency), ADRs, and toxicity. Compliance was verified in all the patients. Levels were found to reduce with the use of concomitant enzyme inducer drugs (56.78%) whereas increase with valproic acid (7.8%).

Conclusion:

These findings emphasize the need for monitoring the serum levels of newer AEDs like LEV considering the various parameters studied here, so as to maintain the therapeutic efficacy by preventing under or over dosage and to generate a broader database of serum levels of LEV in the Indian population to help appropriate prescribing with more confidence.

International Veterinary Epilepsy Task Force consensus proposal: medical treatment of canine epilepsy in Europe

In Europe, the number of antiepileptic drugs (AEDs) licensed for dogs has grown considerably over the last years. Nevertheless, the same questions remain, which include, 1) when to start treatment, 2) which drug is best used initially, 3) which adjunctive AED can be advised if treatment with the initial drug is unsatisfactory, and 4) when treatment changes should be considered. In this consensus proposal, an overview is given on the aim of AED treatment, when to start long-term treatment in canine epilepsy and which veterinary AEDs are currently in use for dogs. The consensus proposal for drug treatment protocols, 1) is based on current published evidence-based literature, 2) considers the current legal framework of the cascade regulation for the prescription of veterinary drugs in Europe, and 3) reflects the authors' experience. With this paper it is aimed to provide a consensus for the management of canine idiopathic epilepsy. Furthermore, for the management of structural epilepsy AEDs are inevitable in addition to treating the underlying cause, if possible.

Effect of chronic administration of phenobarbital, or bromide, on pharmacokinetics of levetiracetam in dogs with epilepsy

BACKGROUND

Levetiracetam (LEV) is a common add-on antiepileptic drug (AED) in dogs with refractory seizures. Concurrent phenobarbital administration alters the disposition of LEV in healthy dogs.

HYPOTHESIS/OBJECTIVES

To evaluate the pharmacokinetics of LEV in dogs with epilepsy when administered concurrently with conventional AEDs.

ANIMALS

Eighteen client-owned dogs on maintenance treatment with LEV and phenobarbital (PB group, n = 6), LEV and bromide (BR group, n = 6) or LEV, phenobarbital and bromide (PB-BR group, n = 6).

METHODS

Prospective pharmacokinetic study. Blood samples were collected at 0, 1, 2, 4, and 6 hours after LEV administration. Plasma LEV concentrations were determined by high-pressure liquid chromatography. To account for dose differences among dogs, LEV concentrations were normalized to the mean study dose (26.4 mg/kg). Pharmacokinetic analysis was performed on adjusted concentrations, using a noncompartmental method, and area-under-the-curve (AUC) calculated to the last measured time point.

RESULTS

Compared to the PB and PB-BR groups, the BR group had significantly higher peak concentration (Cmax ) (73.4 ± 24.0 versus 37.5 ± 13.7 and 26.5 ± 8.96 μg/mL, respectively, P < .001) and AUC (329 ± 114 versus 140 ± 64.7 and 98.7 ± 42.2 h*μg/mL, respectively, P < .001), and significantly lower clearance (CL/F) (71.8 ± 22.1 versus 187 ± 81.9 and 269 ± 127 mL/h/kg, respectively, P = .028).

CONCLUSIONS AND CLINICAL IMPORTANCE

Concurrent administration of PB alone or in combination with bromide increases LEV clearance in epileptic dogs compared to concurrent administration of bromide alone. Dosage increases might be indicated when utilizing LEV as add-on treatment with phenobarbital in dogs.

Pharmacokinetic variability of four newer antiepileptic drugs, lamotrigine, levetiracetam, oxcarbazepine, and topiramate: a comparison of the impact of age and comedication

BACKGROUND

Newer antiepileptic drugs (AEDs) are widely used in patients with epilepsy. There is still insufficient documentation regarding pharmacokinetic variability of these AEDs in different patient groups.

PURPOSE

The purpose of this study was to compare age and comedication as factors contributing to pharmacokinetic variability between 4 newer AEDs (lamotrigine, levetiracetam, oxcarbazepine, and topiramate) among patients with refractory epilepsy.

METHODS

Data regarding age, gender, use of AEDs, daily doses, and serum concentration measurements were retrieved from a therapeutic drug monitoring database, from patients admitted to the National Center for Epilepsy, Norway, 2007-2008.

RESULTS

In total, 1050 patients were included, 111 younger children (2-9 years), 137 older children (10-17 years), 720 adults (18-64 years), 82 elderly (65-93 years). Fifty percent of the patients were prescribed polytherapy, in 88 different combinations. The interindividual pharmacokinetic variability was extensive, as illustrated by a 10-fold variability in serum concentration compared with dose. Age affected the apparent clearance of levetiracetam to the largest extent, as shown by a 60% increase in younger children and a 40% reduction in the elderly, respectively, compared with adults. Comedication altered the clearance of lamotrigine to the greatest extent ±70% because it is affected by both enzyme inducers and inhibitors. Hepatic enzyme inducers increased the clearance of levetiracetam and topiramate by 25% and oxcarbazepine by 75%. Valproic acid reduced the clearance of topiramate by 25%.

CONCLUSION

Age and comedication are important contributors to pharmacokinetic variability. Age had the greatest impact on levetiracetam, and comedication affected the clearance of each of the 4 AEDs investigated in this study. Pharmacokinetic drug interactions must be carefully considered when multidrug therapies are prescribed. Therapeutic drug monitoring is a valuable tool for individualizing AED therapy.

Safety and efficacy of levetiracetam for the treatment of partial onset seizures in children from one month of age

Epilepsy is a common neurological disorder in the pediatric population, affecting up to one percent of children, and for which the mainstay of treatment is anticonvulsant medication. Despite the frequent use of anticonvulsant drugs, remarkably little is known about the safety and efficacy of most of these medications in the pediatric epilepsy population. Of 34 anticonvulsants currently approved for use by the US Food and Drug Administration (FDA), only 13 have been approved for use in children. Although infants and young children are disproportionately affected by epilepsy, there are currently only three anticonvulsant medications that have been specifically evaluated and approved for use in children younger than 2 years of age. In 2012, the FDA approved levetiracetam as an adjunctive treatment for partial onset seizures in infants and children from one month of age. Here we review the available data on levetiracetam in the pediatric epilepsy population. We first discuss the pharmacological profile of levetiracetam, including its mechanism of action, formulations and dosing, and pharmacokinetics in children. We then review the available efficacy, safety, and tolerability data in children from one month of age with partial onset seizures. We conclude that the current data leading to the approval of levetiracetam for use in infants and children with partial onset seizures is encouraging, although more work needs to be done before definitive conclusions can be drawn about the efficacy of levetiracetam across different pediatric age groups.

Levetiracetam: a review of its use in epilepsy

Levetiracetam (Keppra®, E Keppra®) is an established second-generation antiepileptic drug (AED). Worldwide, levetiracetam is most commonly approved as adjunctive treatment of partial onset seizures with or without secondary generalization; other approved indications include monotherapy treatment of partial onset seizures with or without secondary generalization, and adjunctive treatment of myoclonic seizures associated with juvenile myoclonic epilepsy and primary generalized tonic-clonic (GTC) seizures associated with idiopathic generalized epilepsy. Levetiracetam has a novel structure and unique mechanisms of action. Unlike other AEDs, the mechanisms of action of levetiracetam appear to involve neuronal binding to synaptic vesicle protein 2A, inhibiting calcium release from intraneuronal stores, opposing the activity of negative modulators of GABA- and glycin-gated currents and inhibiting excessive synchronized activity between neurons. In addition, levetiracetam inhibits N-type calcium channels. Levetiracetam is associated with rapid and complete absorption, high oral bioavailability, minimal metabolism that consists of hydrolysis of the acetamide group, and primarily renal elimination. It lacks cytochrome P450 isoenzyme-inducing potential and is not associated with clinically significant pharmacokinetic interactions with other drugs, including other AEDs. The efficacy of oral immediate-release levetiracetam in controlling seizures has been established in numerous randomized, double-blind, controlled, multicentre trials in patients with epilepsy. Adjunctive levetiracetam reduced the frequency of seizures in paediatric and adult patients with refractory partial onset seizures to a significantly greater extent than placebo. Monotherapy with levetiracetam was noninferior to that with carbamazepine controlled release in controlling seizures in patients with newly diagnosed partial onset seizures. Levetiracetam also provided seizure control relative to placebo as adjunctive therapy in patients with idiopathic generalized epilepsy with myoclonic seizures or GTC seizures. In addition, patients receiving oral levetiracetam showed improvements in measures of health-related quality of life relative to those receiving placebo. Although treatment-emergent adverse events were commonly reported in the clinical trials of levetiracetam, the overall proportion of patients who experienced at least one treatment-emergent adverse event was broadly similar in the levetiracetam and placebo treatment groups, with most events being mild to moderate in severity. Levetiracetam is not associated with cognitive impairment or drug-induced weight gain, but has been associated with behavioural adverse effects in some patients.

Age and comedications influence levetiracetam pharmacokinetics in children

The pharmacokinetics of many antiepileptic drugs differs between adults and children. The influence of age and concomitant medications on the dose/concentration ratio of levetiracetam was examined in 103 children with epilepsy. Dosing and plasma levels of levetiracetam and concomitant antiepileptic drugs were reviewed retrospectively. The dose/concentration ratio was calculated as the weight-normalized dose (mg/kg/day) divided by the steady-state trough plasma drug level, which was used as a measure of apparent oral clearance of levetiracetam. Children were classified into age groups and treatment groups: levetiracetam given with enzyme inducers (n = 24) or nonenzyme inducers (n = 69), or as monotherapy (n = 10). Levetiracetam clearance differed significantly between age groups (0-4, 5-11, and 12-17 years), i.e., the younger the child, the higher the clearance. The increase was 1.7-fold between the youngest and oldest age groups. Children on enzyme inducers exhibited significantly higher clearance (1.3-fold), compared with those on nonenzyme inducers and monotherapy. Levetiracetam did not influence the clearance of lamotrigine, valproate, topiramate, or clonazepam. In conclusion, younger age and comedication with an enzyme inducer increased levetiracetam clearance. This finding should be taken into account when treating individual patients.

Quality of life and seizure control in patients with brain tumor-related epilepsy treated with levetiracetam monotherapy: preliminary data of an open-label study

The aim of this pilot study was to investigate the effects of levetiracetam monotherapy on seizure control, quality of life and neurocognitive performance in patients with brain tumor-related epilepsy. We present here preliminary data from 18 patients with follow-up of 6 months. We evaluated seizure frequency at baseline. We used administered Mini Mental State Examination (MMSE), Karnofsky Performance Status (KPS), Barthel index (BI), QOLIE 31P (V2), EORTC QLQ-C30 and Adverse Events Profile. After 6 months, 16 patients were seizure free (88.9%), 2 (11.1%) had reduction in seizure frequency >50%. Compared to baseline, we observed a worsening of performance (KPS p = 0.011; BI = 0.008) and global lower cognitive performance (MMSE p = 0.011); distress related to seizure frequency (p = 0.003) and medication effects (p = 0.046) were significantly lower. Levetiracetam caused mild and reversible side effects. These preliminary data on LEV monotherapy in patients with brain tumor-related epilepsy show that this antiepileptic drug is efficacious and well tolerated.

Antiepileptic drug interactions

INTRODUCTION

Antiepileptics are drugs used in the long-term treatment of epilepsy and other conditions such as pain or psychiatric diseases. They are often administered as polytherapy or in combination with other treatments. It is therefore important to know their potential interactions (with each other and with other substances) in order to avoid altering their efficacy or potentiating their side effects.

OBJECTIVE

The purpose of this article is to review these aspects and stress the most important interactions in day-to-day clinical practice.

RESULTS

Older antiepileptic drugs (AEDs) such as phenytoin, carbamazepine, phenobarbital and valproic acid can significantly interfere not only with each other and other AEDs, but also with other treatments. Although newer AEDs have a more favourable pharmacokinetic profile, they are not entirely exempt from interactions and they are also commonly administered in combination with older AEDs. Another aspect that should be considered is the existence of any clinically important pharmacokinetic and pharmacodynamic interactions in patients requiring the continuous administration of other treatments.

CONCLUSION

We must be aware of the pharmacokinetic and pharmacodynamic interactions of AEDs. Because of a lack of significant interactions, drugs such as levetiracetam, gabapentin or pregabalin can be recommended in particular groups such as patients with cancer, transplants, anticoagulant treatments or HIV infection. In all cases, it is important to ensure AED efficacy and prevent serious complications.

Safety and feasibility of switching from phenytoin to levetiracetam monotherapy for glioma-related seizure control following craniotomy: a randomized phase II pilot study

Seizures are common in patients with gliomas, and phenytoin (PHT) is frequently used to control tumor-related seizures. PHT, however, has many undesirable side effects (SEs) and drug interactions with glioma chemotherapy. Levetiracetam (LEV) is a newer antiepileptic drug (AED) with fewer SEs and essentially no drug interactions. We performed a pilot study testing the safety and feasibility of switching patients from PHT to LEV monotherapy for postoperative control of glioma-related seizures. Over a 13-month period, 29 patients were randomized in a 2:1 ratio to initiate LEV therapy within 24 h of surgery or to continue PHT therapy. 6 month follow-up data were available for 15 patients taking LEV and for 8 patients taking PHT. In the LEV group, 13 patients (87%) were seizure-free. In the PHT group, 6 patients (75%) were seizure-free. Reported SEs at 6 months was as follows (%LEV/%PHT group): dizziness (0/14), difficulty with coordination (0/29), depression (7/14) lack of energy or strength (20/43), insomnia (40/43), mood instability (7/0). The pilot data presented here suggest that it is safe to switch patients from PHT to LEV monotherapy following craniotomy for supratentorial glioma. A large-scale, double-blinded, randomized control trial of LEV versus PHT is required to determine seizure control equivalence and better assess differences in SEs.

Antiepileptic drugs--best practice guidelines for therapeutic drug monitoring: a position paper by the subcommission on therapeutic drug monitoring, ILAE Commission on Therapeutic Strategies

Although no randomized studies have demonstrated a positive impact of therapeutic drug monitoring (TDM) on clinical outcome in epilepsy, evidence from nonrandomized studies and everyday clinical experience does indicate that measuring serum concentrations of old and new generation antiepileptic drugs (AEDs) can have a valuable role in guiding patient management provided that concentrations are measured with a clear indication and are interpreted critically, taking into account the whole clinical context. Situations in which AED measurements are most likely to be of benefit include (1) when a person has attained the desired clinical outcome, to establish an individual therapeutic concentration which can be used at subsequent times to assess potential causes for a change in drug response; (2) as an aid in the diagnosis of clinical toxicity; (3) to assess compliance, particularly in patients with uncontrolled seizures or breakthrough seizures; (4) to guide dosage adjustment in situations associated with increased pharmacokinetic variability (e.g., children, the elderly, patients with associated diseases, drug formulation changes); (5) when a potentially important pharmacokinetic change is anticipated (e.g., in pregnancy, or when an interacting drug is added or removed); (6) to guide dose adjustments for AEDs with dose-dependent pharmacokinetics, particularly phenytoin.

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

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.

Effect of Age and Comedication on Levetiracetam Pharmacokinetics and Tolerability

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.

Saliva and Serum Levetiracetam Concentrations in Patients With Epilepsy

Although antiepileptic drug (AED) monitoring in saliva may have some clinical applicability, it has not yet come into routine use. The correlation between levetiracetam (LEV) saliva and serum concentrations also remains unclear. To confirm LEV saliva assay as a useful, noninvasive alternative to serum measurement, we investigated the possible correlation between saliva and serum LEV concentrations. Samples of saliva and blood were collected from 30 patients with epilepsy receiving chronic therapy with LEV as monotherapy or add-on therapy, and LEV concentrations were assayed in saliva and serum. Linear regression analyses showed a close correlation between saliva and serum LEV concentrations (r2 = 0.90; P < 0.001). LEV blood and saliva concentrations were linearly related to daily drug doses (r2 = 0.78 and 0.70; P < 0.01). When data were analyzed for subgroups (patients receiving LEV in monotherapy, as add-on therapy with enzyme-inducer AEDs, and as add-on therapy with noninducer or moderate-inducer AEDs), no significant difference was found between saliva and serum LEV concentrations among groups. These preliminary results indicate that LEV, like other AEDs, can be measured in saliva as an alternative to blood-based assays. Saliva LEV collection and assay is a valid noninvasive, more convenient alternative to serum measurement.

Prospective assessment of levetiracetam pharmacokinetics during dose escalation in 4- to 12-year-old children with partial-onset seizures on concomitant carbamazepine or valproate

PURPOSE

To assess the multiple-dose pharmacokinetics of levetiracetam and its major metabolite ucb L057 in children with partial-onset seizures and determine whether it is affected by adjunctive carbamazepine or valproate. To correlate levetiracetam concentrations in plasma and saliva and to assess its safety and clinical response.

METHODS

Design was an open-label, multicenter study. Twenty-one children (4-12 years old) with epilepsy taking carbamazepine (13) or valproate (8) received adjunctive levetiracetam. Levetiracetam was initiated at 20 mg/(kg day) and titrated at 2-week intervals to 40 and then 60 mg/(kg day). Twelve-hour pharmacokinetics were determined at the end of each 2-week period. Efficacy was estimated from the partial seizure frequency per week and Global Evaluation Scale.

RESULTS

Levetiracetam was rapidly absorbed following oral dosing, with median t(max) of 0.5 h. Dose proportional increases were observed for C(max) and AUC((0-12)) over the dose range; t(1/2) was 4.9 h. Pharmacokinetics of levetiracetam and ucb L057 were not markedly different with concomitant carbamazepine or valproate; clearance was only 7-13% faster and AUC was decreased by only 15-24% in those on carbamazepine compared to valproate. Levetiracetam did not affect trough carbamazepine or valproate. Concentration in saliva and plasma were strongly correlated. Seizure frequency declined by 50% or more in 43% of subjects in the intent-to-treat population (n=21) and in 56% of those with seizures at baseline (n=16). Marked or moderate improvement occurred in 80% and 75% of patients based on Global Evaluation Scale ratings by investigators and parents/guardians, respectively. Levetiracetam was well tolerated.

CONCLUSION

Levetiracetam exhibits simple pharmacokinetics in children, with rapid absorption and dose-proportional kinetics. Small but not clinically relevant differences were observed between subjects receiving carbamazepine and valproate, suggesting significant dose adjustment is usually not necessary. This substantiates prior assessments that levetiracetam clearance is higher in children than adults, necessitating a higher dose in children on a mg/kg basis, and suggests it is useful add-on therapy for children with partial-onset seizures regardless of baseline therapy.

Population Pharmacokinetics of??Levetiracetam in Japanese and??Western Adults

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.

Levetiracetam therapy in patients with brain tumour and epilepsy

Epilepsy is a common clinical problem in patients with brain tumours, strongly affecting patients' quality of life. Tumour-related seizures are often difficult to control, and the clinical picture is complicated by frequent interactions between antiepileptic drugs (AEDs) and antineoplastic agents. We studied the safety and efficacy of levetiracetam (LEV), a new AED with a different pharmacological profile from traditional anticonvulsants, in 19 patients (6 females; age range 28-70 years, mean 48 years) with supratentorial gliomas and epilepsy. Seizure types were simple partial in four patients, complex partial in 4, complex partial with secondary generalization in 7, and generalized tonic-clonic in 4. LEV was added to the existing AED treatment on account of persisting seizures, and titrated at dosages of 1,000-3,000 mg/day. Patients were seen at the Outpatient's Centre every 1-3 months, and followed-up for 7-50 months (mean 25 months, median 20 months). At the end of the observation period, nine patients were seizure free (seizure free period ranging from 7 to 33 months, mean 16, median 12) and five patients reported an improvement in seizure-frequency from daily to weekly (n=1) or from weekly to monthly (n=3). Seizure frequency was unmodified in four patients and increased (from monthly to weekly) in one. No LEV-related adverse effects were observed. LEV plasma concentrations monitored in 12 subjects ranged from 11.9 to 82.1 microg/ml. Our preliminary open data indicate that add-on treatment with LEV in patients with brain tumours is safe and appears to be effective in reducing seizure frequency. Controlled studies on larger populations are warranted to confirm these open observations.

Onset of Action of Levetiracetam: A RCT Trial Using Therapeutic Intensive Seizure Analysis (TISA)

OBJECTIVES

To correlate the onset of clinical effects of add-on levetiracetam (LEV) therapy with daily serum LEV concentration, in pharmaco-resistant focal epilepsies, using the TISA method.

METHODS

25 adult patients (aged>6 years) with pharmaco-resistant focal epilepsies undergoing presurgical evaluation at the Epilepsy Center Erlangen were enrolled in the study. Eligible patients on a maximum of one other antiepileptic drug (AED) were recruited into the 48-hour baseline phase. Those who had at least two seizures during this phase were randomized into the seven-day treatment phase, when they received either LEV or placebo, under continuous day-and-night video-EEG monitoring. The starting daily dose of LEV was 500 mg bid, titrated from the second treatment day to 1,000 mg bid. The peak serum concentration of LEV was monitored daily at 8:00 am (one hour after drug administration) for every patient. The number and duration of seizures per 24h (N/24h and D/24h respectively) were investigated.

RESULTS

23 patients completed the study (LEV group n=11 and placebo group n=12). Seven patients in the LEV group and two patients in the placebo group achieved seizure-freedom during the treatment phase. The intergroup comparison of the decrease in N/24h and D/24h from the baseline phase to the treatment phase was in favor of the LEV group (p<0.05). A significant effect of LEV on D/24h was seen as early as the second treatment day (p=0.013), becoming more apparent on the third treatment day (p=0.009).

CONCLUSION

The present study objectively quantified the correlation between the anticonvulsant effects of LEV in focal epilepsies and the peak serum concentration of the drug. For the first time, direct measurement was used to demonstrate the onset of action of LEV to be two days after drug initiation.

Pharmacokinetic Variability of Newer Antiepileptic Drugs

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.

Can Pharmacokinetic Variability Be Controlled for the Patient??s Benefit?

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.