Oxcarbazepine: pharmacokinetic interactions and their clinical relevance

The use of carbamazepine to expedite the metabolism of a long-acting aripiprazole injection

WHAT IS KNOWN AND OBJECTIVE

Long-acting injectable (LAI) antipsychotics are an integral part of mental health treatment. Modifying an LAI regimen poses several challenges because of the extended half-life of the drug.

CASE SUMMARY

An acutely psychotic patient with schizoaffective disorder received aripiprazole lauroxil without resolution of symptoms. She was started on a previously successful regimen of oral fluphenazine. Due to continued psychosis, oral carbamazepine was initiated to expedite the LAI's metabolism allowing subsequent doses of fluphenazine to impart activity.

WHAT IS NEW AND CONCLUSION

Potent cytochrome enzyme inducers may help in transitioning patients from LAI antipsychotics to other therapies.

Population pharmacokinetics of oxcarbazepine: a systematic review

INTRODUCTION

Oxcarbazepine is commonly used as first-line treatment for partial and generalized tonic-clonic seizures. Owing to the high pharmacokinetic variability, several population pharmacokinetic models have been developed for oxcarbazepine to explore potential covariates that affect its pharmacokinetic variation.

AREAS COVERED

This review summarizes the published population pharmacokinetic studies of oxcarbazepine in children and adults available in PubMed and Embase databases. The quality of the retrieved studies was evaluated, and significant covariates that may have an impact on the dosage regimen of oxcarbazepine were explored.

EXPERT OPINION

The pharmacokinetics of oxcarbazepine was founded to be affected by body weight and co-administration with enzyme inducers. Pediatric patients require a higher dose per kilogram than adults because children generally have a higher clearance than adults. Moreover, to maintain the target concentration, patients co-administrate with enzyme inducers need a higher dose than monotherapy due to higher clearance in those patients. Because limited information is available for exposure-response relationship, additional pharmacokinetic/pharmacodynamics investigations of oxcarbazepine need to be conducted to optimize the dosage regimen in clinical practice.

Association between HLA-A*3201 allele and oxcarbazepine-induced cutaneous adverse reactions in Eastern Han Chinese population

PURPOSE

To determine genetic associations between oxcarbazepine (OXC)-induced cutaneous adverse drug reactions (cADRs) and human leukocyte antigen (HLA) variants in the Eastern Han Chinese population.

METHODS

A total of 120 patients were enrolled in this study, including 30 subjects with OXC-induced cADRs (case group) and 90 OXC-tolerant patients (control group). High-resolution HLA genotyping was conducted for HLA-A, HLA-B, HLA-C, and HLA-DRB1, and allele frequencies were compared.

RESULTS

No patient carried the HLA-B *1502 allele in the case group, the frequency of HLA-B *1502 allele in the control group was 6.1%. HLA-A*3201 allele was detected in 13.3% of 30 patients with OXC-induced cADRs (4/30) and 0% of 90 OXC-tolerant patients (0/90). The difference in HLA-A*3201 frequency between the two groups was statistically significant [P = 0.004, odds ratio (OR) = 15.877, 95% confidence interval (CI) = 1.817-138.720].

CONCLUSIONS

Eastern Han Chinese patients with the HLA-A*3201 allele may be more susceptible to OXC-induced cADRs, while the HLA-B*1502 allele is not correlated with it. The precise association between HLA alleles and OXC-induced cADRs warrants further study.

Oxcarbazepine extended-release formulation in epilepsy

Oxcarbazepine (OXC) is a 10-keto-analogue of carbamazepine, which was developed and labeled as a follow-up antiepileptic drug, that was intended to overcome some of the pharmacological drawbacks of carbamazepine with similar efficacy. The main advantage is the nonoxidative metabolic pathway that allows a lower enzyme-induction profile and fewer drug interactions. OXC is rapidly and extensively reduced by cytosolic hepatic enzymes to its monohydroxylated derivative (MHD), thus OXC may be regarded as a prodrug with MHD representing the active antiepileptic agent. The immediate-release (IR) formulation of OXC (Trileptal(®), Timox(®)) has an almost complete bioavailibilty. It is rapidly absorbed and reaches peak concentrations after 1-3 h. MHD peak concentrations are measured within 4-12 h. Elimination half-life in healthy subjects is 1-5 h for OXC and 7-20 h for MHD. The OXC plasma concentration peak may have been responsible for side effects, such as dizziness, vertigo, coordination problems or blurred vision, which appeared more often with this formulation in individual cases than with the formulation available prior to 2000, or with another formulation that has been distributed in Scandinavian countries. Both possibilities offer a profile approaching the characteristics of an extended-release (ER) formulation. ER OXC was labeled in Germany in 2008 (Apydan(®) extent, Desitin Arzneimittel GmbH, Hamburg, Germany). Under steady-state conditions, Phase I studies show bioequivalence between IR and ER OXC. With ER OXC, OXC plasma peak concentrations and both OXC and MHD peak-trough fluctuations are markedly reduced. In clinical trials, comparisons between IR OXC twice daily versus ER OXC once daily failed to show significant differences; efficacy tended to be better with IR OXC, whereas OXC ER showed insignificant tolerability advantages. Another study is currently ongoing to compare the tolerability of both formulations under twice-daily administration conditions in patients with difficult-to-treat epilepsies who require a dosage increase of OXC and who are randomized to IR or ER OXC.

Adverse effects of antiepileptic drugs

More than 150 years after bromide was introduced as the first antiepileptic drug, adverse effects remain a leading cause of treatment failure and a major determinant of impaired health-related quality of life in people with epilepsy. Adverse effects can develop acutely or many years after starting treatment and can affect any organ or structure. In the past two decades, many efforts have been made to reduce the burden of antiepileptic drug toxicity. Several methods to screen and quantify adverse effects have been developed. Patient profiles associated with increased risk of specific adverse effects have been uncovered through advances in the areas of epidemiology and pharmacogenomics. Several new-generation antiepileptic drugs with improved tolerability profiles and reduced potential for drug interaction have been added to the therapeutic armamentarium. Overall, these advances have expanded the opportunities to tailor treatment with antiepileptic drugs, to enhance effectiveness and minimise the risk of toxic effects.

Short-term impact of the switch from immediate-release to extended-release oxcarbazepine in epilepsy patients on high dosages

Extended-release oxcarbazepine (OXC) was introduced in Germany in January of 2008. In principle, this formulation should allow a better tolerability due to the less marked serum peak concentration of OXC prior to metabolization to its monohydroxy derivate (MHD) that is the active compound. Twenty-seven in-patients who had been referred to our epilepsy centre because of their difficult-to-treat localization-related epilepsies and had been on immediate-release OXC were abruptly switched to extended-release OXC at identical dosages. The adverse event profile (AEP) and the QOLIE-10 questionnaire were obtained immediately prior to and 5 days after this switch. On both days MHD fasting serum concentrations were also measured. After the switch a significant improvement of tolerability and quality of life was reported according to AEP and QOLIE-10 (p<0.001). Ameliorations were apparent in almost every patient (AEP: 26 of 27 patients, QOLIE-10: 23 of 27 patients). The improvement not explained by a drop of MHD levels. On the contrary and in line with preclinical data, serum levels of MHD rose significantly (p<0.001). We suggest that patients on extended-release OXC experience a lower serum concentration peak of the pro-drug OXC.

Evidence-based guidelines for treating bipolar disorder: revised second edition--recommendations from the British Association for Psychopharmacology

The British Association for Psychopharmacology guidelines specify the scope and target of treatment for bipolar disorder. The second version, like the first, is based explicitly on the available evidence and presented, like previous Clinical Practice guidelines, as recommendations to aid clinical decision making for practitioners: they may also serve as a source of information for patients and carers. The recommendations are presented together with a more detailed but selective qualitative review of the available evidence. A consensus meeting, involving experts in bipolar disorder and its treatment, reviewed key areas and considered the strength of evidence and clinical implications. The guidelines were drawn up after extensive feedback from participants and interested parties. The strength of supporting evidence was rated. The guidelines cover the diagnosis of bipolar disorder, clinical management, and strategies for the use of medicines in treatment of episodes, relapse prevention and stopping treatment.

The role side effects play in the choice of antiepileptic therapy in brain tumor-related epilepsy: a comparative study on traditional antiepileptic drugs versus oxcarbazepine

Background

Seizure control doesn't represent the only challenging goal in patients with brain tumor-related epilepsy. Side effects have often taken precedence for patients' quality of life.

Methods

We performed an observational retrospective study on patients with brain tumor-related epilepsy: 35 who had assumed oxcarbazepine monotherapy and 35 patients who had undergone treatment with traditional antiepileptic drugs. Primary variable of efficacy was the mean seizure frequency per month and safety variables were the drop-out for side effects and total incidence of side effects. We applied the Propensity Score technique to minimize selection bias.

Results

Our results showed a similar efficacy of oxcarbazepine and traditional antiepileptic drugs over time, but the difference in safety and tolerability between the two groups was significant: traditional AEDs caused more side effects, both serious and non serious.

Conclusion

This study highlights the importance of taking into consideration not only seizure control but also the appearance of side effects when choosing antiepileptic drugs in this patients population.

Interference by carbamazepine and oxcarbazepine with serum- and urine-screening assays for tricyclic antidepressants

OBJECTIVE

The purpose of this work was to evaluate the potential cross-reactivity of 2 antiepileptic medications containing 3-ringed structures, namely, carbamazepine and oxcarbazepine, with screening assays for tricyclic antidepressants.

METHODS

A cross-sectional study of 52 patients between 3 and 19 years of age who had been prescribed either carbamazepine or oxcarbazepine was conducted. A serum fluorescence-polarized immunoassay and a urine enzyme-linked immunoassay were used. The serum carbamazepine or oxcarbazepine level was measured. Gas chromatography/mass spectrometry, a confirmatory test for tricyclic antidepressant detection, was subsequently performed on the serum specimen.

RESULTS

A linear dependency on medication level was observed with the serum fluorescence-polarized immunoassay assay. This relationship was stronger for carbamazepine (4.2 microg/L tricyclic antidepressant detected per microgram/liter of carbamazepine) than for oxcarbazepine (0.7 microg/L tricyclic antidepressant detected per milligram/liter). At higher carbamazepine levels (8.0-11.6 mg/L), 12 of 13 patients had a positive serum fluorescence-polarized immunoassay result; at lower levels (0.1-7.9 mg/L), only 1 of 20 had a positive result. None of the patients who were receiving oxcarbazepine showed significant tricyclic antidepressant activity on either assay.

CONCLUSIONS

Carbamazepine interferes at a statistically significant level with serum fluorescence-polarized immunoassay assay and in a dose-dependent fashion. Neither carbamazepine nor oxcarbazepine exhibit significant tricyclic antidepressant activity on urine enzyme-linked immunoassay assay.

A Comparative Pharmacokinetic Study in Healthy Volunteers of the Effect of Carbamazepine and Oxcarbazepine on Cyp3a4

PURPOSE

Carbamazepine (CBZ) and oxcarbazepine (OXCZ) are well-known inducers of drug metabolism via CYP3A4. Indirect interaction studies and clinical experience suggest that CBZ has a stronger potential in this regard than OXCZ. However this has never been subject to a direct comparative study. We performed a study in healthy volunteers to investigate the relative inductive effect of CBZ and OXCZ on CYP3A4 activity using the metabolism of quinidine as a biomarker reaction.

METHODS

Ten healthy, male volunteers participated in an open, randomized crossover study consisting of two periods separated by a 4-week wash-out period. The subjects received 1200 mg oral OXCZ daily for 17 days and 800 mg oral CBZ for 17 days. A single 200 mg oral dose of quinidine was administered at baseline and following administration of CBZ and OXCZ. Outcome parameters were the formation clearance of 3-hydroxyquinidine dose and the ratio of the AUCs of 3-hydroxyquinidine to quinidine.

RESULTS

Formation clearance of 3-hydroxyquinidine was increased by means of 89% (CI: 36-164; p=0.0022) and 181% (CI: 120-260, p<0.0001) after treatment with OXCZ and CBZ, respectively, compared to baseline. The relative inductive effect of CBZ was 46% higher than for OXCZ. AUC ratio increased by means of 161% (CI: 139-187, p<0.0001) (OXCZ) and 222% (CI: 192-257, p<0.0001) (CBZ). Quinidine Cmax decreased by means of 29% (CI: 16-40, p=0.0018) (OXCZ) and 33% (CI: 18-45, p=0.0020) (CBZ). T1/2 decreased by means of 12% (CI: 6-17, p<0.0014) (OXCZ) and 32% (CI: 25-38, p<0.0001) (CBZ). tmax was not changed in either period.

CONCLUSION

We confirm a clinically significant inductive effect of both OXCZ and CBZ. The inductive effect of CBZ was about 46% higher than that of OXCZ, a difference that may be of clinical relevance.

Novel anticonvulsant drugs

Principles of complex mechanisms of action of anticonvulsants including latest reports concerning new antiepileptic drugs (AED) are considered. Different aspects of new anticonvulsant drugs (2nd generation) from preclinical and clinical testing, pharmacokinetics, and mono or combination therapy in children and adults are summarized. In the following condensed synopsis pharmacological and clinical characteristics of gabapentin (GBP), lamotrigine (LTG), levetiracetam (LEV), oxcarbazepine (OXC), pregabalin (PGB) and tiagabine (TGB) as well as topiramate (TPM) and zonisamide (ZNS) are discussed. In addition to the mechanisms of action, pharmacokinetics, interactions, indications and dosages as well as side effects are considered. Important data concerning the effect and tolerability of anticonvulsant drugs can be obtained from controlled studies. In comparison to drugs of the first generation (phenobarbital [PB], primidon [PRD], phenytoin [PHT], carbamazepine [CBZ] and valproic acid [VPA]) the potential for interactions and side effects due to enzyme induction or inhibition is reduced by most of the anticonvulsant drugs of the second generation. New anticonvulsant drugs increase the spectrum of treatment and represent further steps with regard to the optimization of an individual therapy of the epilepsies.

Development and validation of a high performance liquid chromatographic method for the determination of oxcarbazepine and its main metabolites in human plasma and cerebrospinal fluid and its application to pharmacokinetic study

An isocratic reversed-phase HPLC-UV procedure for the determination of oxcarbazepine and its main metabolites 10-hydroxy-10,11-dihydrocarbamazepine and 10,11-dihydroxy-trans-10,11-dihydrocarbamazepine in human plasma and cerebrospinal fluid has been developed and validated. After addition of bromazepam as internal standard, the analytes were isolated from plasma and cerebrospinal fluid by liquid-liquid extraction. Separation was achieved on a X-TERRA C18 column using a mobile phase composed of 20 mM KH(2)PO(4), acetonitrile, and n-octylamine (76:24:0.05, v/v/v) at 40 degrees C and detected at 237 nm. The described assay was validated in terms of linearity, accuracy, precision, recovery and lower limit of quantification according to the FDA validation guidelines. Calibration curves were linear with a coefficient of variation (r) greater than 0.998. Accuracy ranged from 92.3% to 106.0% and precision was between 2.3% and 8.2%. The method has been applied to plasma and cerebrospinal fluid samples obtained from patients treated with oxcarbazepine, both in monotherapy and adjunctive therapy.

Use of Antiepileptic Drugs in Patients with Kidney Disease

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.

Clinically relevant drug interactions with antiepileptic drugs

Some patients with difficult-to-treat epilepsy benefit from combination therapy with two or more antiepileptic drugs (AEDs). Additionally, virtually all epilepsy patients will receive, at some time in their lives, other medications for the management of associated conditions. In these situations, clinically important drug interactions may occur. Carbamazepine, phenytoin, phenobarbital and primidone induce many cytochrome P450 (CYP) and glucuronyl transferase (GT) enzymes, and can reduce drastically the serum concentration of associated drugs which are substrates of the same enzymes. Examples of agents whose serum levels are decreased markedly by enzyme-inducing AEDs, include lamotrigine, tiagabine, several steroidal drugs, cyclosporin A, oral anticoagulants and many cardiovascular, antineoplastic and psychotropic drugs. Valproic acid is not enzyme inducer, but it may cause clinically relevant drug interactions by inhibiting the metabolism of selected substrates, most notably phenobarbital and lamotrigine. Compared with older generation agents, most of the recently developed AEDs are less likely to induce or inhibit the activity of CYP or GT enzymes. However, they may be a target for metabolically mediated drug interactions, and oxcarbazepine, lamotrigine, felbamate and, at high dosages, topiramate may stimulate the metabolism of oral contraceptive steroids. Levetiracetam, gabapentin and pregabalin have not been reported to cause or be a target for clinically relevant pharmacokinetic drug interactions. Pharmacodynamic interactions involving AEDs have not been well characterized, but their understanding is important for a more rational approach to combination therapy. In particular, neurotoxic effects appear to be more likely with coprescription of AEDs sharing the same primary mechanism of action.

Prevention of early postoperative seizures in patients with primary brain tumors: preliminary experience with oxcarbazepine

Early postoperative seizures are defined as those that appear within the first week after surgery and are a well-known and feared complication in patients with supratentorial brain tumors. Few studies have investigated the value of pharmacological prophylaxis in the prevention of postoperative seizures in these patients and their outcome has not been consistent. Furthermore, the efficacy of the new generation of antiepileptic agents in the prophylaxis of perioperative seizures has not been assessed so far. We analyzed the data related to 150 patients harboring supratentorial brain gliomas with the aim to assess the efficacy of oxcarbazepine in preventing the occurrence or the recurrence of early postoperative seizures and its tolerability when it is rapidly titrated. Only four patients (2.7%) experienced seizures within the first week after surgery. Patients did not report disturbances during the titration phase. Regarding adverse events in the first week, six patients (4%) showed minor skin rash. Persistent symptomatic hyponatremia never occurred. Our data showed that oxcarbazepine can be a good alternative to traditional antiepileptic agents in the prevention of perioperative seizures being efficacy, ease of use (rapid titration in 3 days, not requiring close plasma concentration monitoring) and good tolerability (no major side effects during titration and during the first postoperative week) the key factors. Moreover, oxcarbazepine can be a valid choice when long-term therapy is required because of the low interaction with other drugs and the low hematological side effects.

Effects of oxcarbazepine and phenytoin on the EEG and cognition in healthy volunteers

We studied the EEG and cognitive effects of oxcarbazepine (OXC) and phenytoin (PHT) using a double-blind, randomized, parallel-group design. Thirty-two healthy volunteers received a maximum of 1200 mg of OXC or 360 mg of PHT. EEG and cognitive testing were performed at baseline and after 12 weeks of treatment. For each subject and measure, test-retest Z scores were calculated from regression equations derived from 73 healthy controls. Twenty-six subjects completed the study. Both the OXC and PHT groups had significant slowing of the EEG peak frequency and increased relative theta and delta power. Differences between AEDs (antiepileptic drugs) were not significant. Significant cognitive effects were seen on 5 of 20 measures, primarily measures of motor speed and reaction time. Again, there were no significant differences between AEDs. The only significant difference between AEDs was for the POMS-Vigor scale, favoring OXC. The small sample size may have contributed to the lack of significant differences between AEDs.

What is the evidence that oxcarbazepine and carbamazepine are distinctly different antiepileptic drugs?

Oxcarbazepine (OXC, Trileptal) is a modern antiepileptic drug (AED) used as both monotherapy and adjunctive therapy for the treatment of partial seizures with or without secondary generalization in adults and children above 4 years (USA) or 6 years (Europe) of age. Although OXC has been developed through structural variation of carbamazepine (CBZ) with the intent to avoid metabolites causing side effects, significant differences have emerged between the two drugs. The mechanism of action of OXC involves mainly blockade of sodium currents but differs from CBZ by modulating different types of calcium channels. In contrast to CBZ, which is oxidized by the cytochrome P-450 system, OXC undergoes reductive metabolism at its keto moiety to form the monohydroxy derivative (MHD), which is glucuronidated and excreted in the urine. The involvement of the hepatic cytochrome P-450-dependent enzymes in the metabolism of OXC is minimal. Although it does not prevent interaction with oral contraceptives, it explains why OXC can be more effectively combined with other AEDs such as valproate compared with CBZ. Switching from CBZ to OXC normalized CBZ-associated thyroid and sexual hormone abnormalities and pathological lipid values in small patient samples. OXC is often better tolerated than CBZ and causes fewer rashes than CBZ. Add-on or substitution treatment with OXC was effective in controlled trials even when CBZ did not achieve sufficient seizure control. This constitutes compelling clinical evidence that OXC and CBZ are distinctly different medications. From postmarketing experience in over 1,000,000 patient years, OXC had an advantageous risk-benefit balance also in comparison to other new AEDs. OXC should be preferred over CBZ and other older AEDs because of its proven efficacy and excellent side effect profile in children, adolescents, and adults with partial seizures.

Clinical pharmacokinetics of oxcarbazepine

Oxcarbazepine is an antiepileptic drug with a chemical structure similar to carbamazepine, but with different metabolism. Oxcarbazepine is rapidly reduced to 10,11-dihydro-10-hydroxy-carbazepine (monohydroxy derivative, MHD), the clinically relevant metabolite of oxcarbazepine. MHD has (S)-(+)- and the (R)-(-)-enantiomer, but the pharmacokinetics of the racemate are usually reported. The bioavailability of the oral formulation of oxcarbazepine is high (>95%). It is rapidly absorbed after oral administration, reaching peak concentrations within about 1-3 hours after a single dose, whereas the peak of MHD occurs within 4-12 hours. At steady state, the peak of MHD occurs about 2-4 hours after drug intake. The plasma protein binding of MHD is about 40%. Cerebrospinal fluid concentrations of MHD are in the same range as unbound plasma concentrations of MHD. Oxcarbazepine can be transferred significantly through the placenta in humans. Oxcarbazepine and MHD exhibit linear pharmaco-kinetics and no autoinduction occurs. Elimination half-lives in healthy volunteers are 1-5 hours for oxcarbazepine and 7-20 hours for MHD. Longer and shorter elimination half-lives have been reported in elderly volunteers and children, respectively. Mild to moderate hepatic impairment does not appear to affect MHD pharmacokinetics. Renal impairment affects the pharmacokinetics of oxcarbazepine and MHD. The interaction potential of oxcarbazepine is relatively low. However, enzyme-inducing antiepileptic drugs such as phenytoin, phenobarbital or carbamazepine can reduce slightly the concentrations of MHD. Verapamil may moderately decrease MHD concentrations, but this effect is probably without clinical relevance. The influence of oxcarbazepine on other antiepileptic drugs is not clinically relevant in most cases. However, oxcarbazepine appears to increase concentrations of phenytoin and to decrease trough concentrations of lamotrigine and topiramate. Oxcarbazepine lowers concentrations of ethinylestra-diol and levonorgestrel, and women treated with oxcarbazepine should consider additional contraceptive measures. Due to the absent or lower enzyme-inducing effect of oxcarbazepine, switching from carbamazepine to oxcarbazepine can result in increased serum concentrations of comedication, sometimes associated with adverse effects. The effect of oxcarbazepine appears to be related to dose and to serum concentrations of MHD. In general, daily fluctuations of MHD concentration are relatively slight, smaller than would be expected from the elimination half-life of MHD. However, relatively high fluctuations can be observed in individual patients. Therapeutic monitoring may help to decide whether adverse effects are dependent on MHD concentrations. A mean therapeutic range of 15-35 mg/L for MHD seems to be appropriate. However, more systematic studies exploring the concentration-effect relationship are required.

Adjunctive oxcarbazepine in comorbid anxiety and affective disorder with hyponatremic seizure: case analysis and literature review

Rational polypharmacy is required for management of refractory psychiatric disorders. Antiepileptic drugs are increasingly used as primary or adjunctive agents in the treatment of affective, schizoaffective, anxiety, and impulse control disorders. In this case report, the authors present the first case of hyponatremic seizure associated with oxcarbazepine in adjunctive treatment of comorbid affective/anxiety disorders.

New anticonvulsant medication uses in bipolar disorder

Therapy of bipolar disorders is a rapidly evolving field. Lithium has efficacy in classic bipolar disorders whereas divalproex sodium and carbamazepine may have broader spectrum efficacy that includes non-classic bipolar disorder. In the last 10 years, a series of anticonvulsants have been approved for marketing in the United States. Gabapentin has indirect g-aminobuytric acid-ergic actions, is generally well tolerated, and appears to have anxiolytic, analgesic, and hypnotic effects. Lamotrigine has antiglutamatergic actions and is generally well tolerated (aside from rash in 1 in 10, and serious rash in 1 in 1,000 patients). Lamotrigine is indicated for maintenance treatment in bipolar disorder. Emerging evidence suggests lamotrigine may have utility in bipolar disorder patients with depression and treatment-refractory rapid cycling, as well as analgesic effects. Topiramate and zonisamide may allow both weight loss, while topiramate may have specific efficacy in bulimia, binge eating disorder, and alcohol dependence. Two small studies found oxcarbazepine had similar efficacy to lithium and haloperidol in acute mania. Phenytoin, an older anticonvulsant, may have adjunctive acute mania efficacy. Levetiracetam, a newer anticonvulsant, may be worth exploring and has minimal drug-drug interactions. None of these newer agents has been shown effective in a large placebo controlled trial for acute mania. Although the clinical profiles of these newer anticonvulsants do not appear to overlap markedly with divalproex and carbamazepine (except perhaps for oxcarbazepine), these novel agents may still offer important new options in relieving a variety of specific target symptoms in patients with bipolar disorder.

Safety and tolerability of oxcarbazepine in elderly patients with epilepsy

Despite the high incidence of seizures and epilepsy in the elderly, the tolerability and safety of anticonvulsants are rarely evaluated in this patient population. We compared the safety and tolerability of oxcarbazepine in a cohort of 52 patients aged 65 years and older and a group of 1574 adult patients ranging in age between 18 and 64 years. There was no significant difference between the two groups with respect to premature discontinuation due to adverse events. The four most common adverse events experienced by patients in the elderly group, irrespective of their causal relationship to oxcarbazepine, were vomiting (19%), dizziness (17%), nausea (17%), and somnolence (15%). Three patients developed an asymptomatic hyponatremia, with at least one serum sodium level below 125mEq/L. Elderly patients on concomitant natriuretic drugs were significantly more likely to develop serum sodium levels below 135mEq/L. The results indicate that oxcarbazepine is safe to use in elderly patients and that its tolerability in this age group is similar to that of younger adult patients.

Liquid chromatographic determination of oxcarbazepine and its metabolites in plasma of epileptic patients after solid-phase extraction

A method based on high-performance liquid chromatography with UV detection in combination with solid-phase extraction for sample pretreatment has been developed for the simultaneous analysis of the antiepileptic drug oxcarbazepine and its main metabolites in human plasma. The extraction of the analytes from plasma samples was carried out by means of a selective solid-phase extraction procedure using hydrophilic-lipophilic balance cartridges. The separation was obtained on a reversed-phase column (C(18), 150x4.6 mm I.D., 5 micrometer) using a phosphate buffer-acetonitrile-methanol-triethylamine mixture (final apparent pH* 3.5) as the mobile phase. Under these chromatographic conditions, oxcarbazepine and its metabolites 10,11-dihydro-10-hydroxycarbamazepine, 10,11-dihydro-10,11-dihydroxycarbamazepine and the internal standard are baseline separated in less than 9 min. The extraction yield values were >94% for all analytes and the precision, expressed by the RSD%, was in the low percentage range. For the entire method, including sample pre-treatment and HPLC determination, the linearity of the calibration lines, expressed by the linear correlation coefficient, was better than 0.995; the limit of quantitation was 15 ng ml(-1). The method was applied to plasma samples from patients undergoing chronic treatment with oxcarbazepine, both in monotherapy and in polytherapy. Based on the analytical parameters precision, accuracy, limit of quantitation and analysis time the method is suitable for routine application in therapeutic drug monitoring.

Oxcarbazepine versus Divalproex Sodium for the Continuing Treatment of Mania

BACKGROUND AND OBJECTIVE

Oxcarbazepine, an antiepileptic and a derivative of carbamazepine, has been shown to have clinical utility as an antimanic agent. This study sought to assess the efficacy and tolerability of oxcarbazepine compared with divalproex sodium in the treatment of patients with mania.

PATIENTS AND METHODS

57 patients from a large clinical practice who had recently begun treatment with divalproex sodium were randomly assigned to one of two treatment groups. In this open-label, single (rater)-blind study, group 1 remained on treatment with divalproex sodium and group 2 was switched to oxcarbazepine. Both treatment groups were followed for 10 weeks after the switch. Pharmacotherapeutic efficacy was compared using the Clinician Administered Rating Scale for Mania (CARS-M). Weight and adverse events were monitored throughout the study.

RESULTS

83% of patients using oxcarbazepine showed a decrease in mania as assessed using the CARS-M, and 70% showed a net decrease in weight over the 10-week course of the study. For the divalproex sodium group, 53% showed a decrease in mania, as assessed by CARS-M, and 37% lost weight.

CONCLUSION

Oxcarbazepine showed comparable efficacy to divalproex sodium, yet appeared to do so with an equal or more benign side-effect profile, particularly with regard to weight. These results suggest that oxcarbazepine, which has been used in Europe for the treatment of mood disorders for some time (albeit used off-label for this purpose) may show promise for use in the US as an agent for maintenance of non-acute mania.

Acute antimanic efficacy and safety of oxcarbazepine in an open trial with an on-off-on design

RATIONALE AND OBJECTIVES

Carbamazepine has shown reasonable antimanic properties, but its use has been limited because of enzyme-inducing effects. The keto-derivative oxcarbazepine (OXC) is very similar to carbamazepine, however, the metabolic pathway is different. OXC is not metabolized to the 10, 11-epoxide, which seems to be responsible for several undesirable side-effects of carbamazepine and furthermore OXC has less enzyme-inducing properties.

METHODS

In this non-random open label study, patients were treated with OXC for 14 days, crossed over to no OXC for 7 days, and then crossed back over to OXC for the remaining 14 days. OXC was titrated to a final dose in a range of 900-2100 mg due to individual response. Treatment success was defined as a reduction of the original Young Mania Rating Scale (YMRS) score of more than 50% at the end of study period.

RESULTS

Four of the 12 included patients (33%) met defined response criteria at the end of study period. Fifty percentage of the patients had to be prematurely excluded from the trial. The mean YMRS scores of the on-periods were obviously different from the off-period. Forty-two percentage of the patients experienced side-effects leading to premature discontinuation in two of 12 patients.

CONCLUSION

Antimanic activity of OXC was demonstrated in this pilot study only for patients with mild or moderate manic symptoms. Further studies are encouraged to clarify OXC's role as mood-stabilizer and assess whether it has a profile similar to that of carbamazepine.

New antiepileptic drug therapies

The introduction of these new antiepileptic drugs, from felbamate to levetiracetam, raised hope of control of epilepsy with fewer adverse effects and improved quality of life. Unfortunately, many patients continue to experience refractory epilepsy despite the use of these new agents, and dose-related adverse effects and idiosyncratic reactions continue to be problematic. A recent report describes six new compounds in preclinical development, and five in clinical trials [131]. As the number of available, effective, but imperfect antiepileptic drugs increases, many challenges remain. These include: choosing the drug appropriate for the epileptic syndrome, assessing accurately the range of a drug's adverse effects in an individual patient, and considering carefully the drug's interactions in combination drug therapy. In considering drug combinations, differing mechanisms of drug action and favorable pharmacodynamic interactions (an area requiring additional studies) are of importance. Clinicians caring for children who have epilepsy anticipate further advances in the pharmacogenetics and molecular pathophysiology of epilepsy, leading to individually tailored, effective, and safe therapy.

LC determination of oxcarbazepine and its active metabolite in human serum

Twenty-five percent of epileptic patients present refractory seizures to current frontline antiepileptic drugs, needing new treatments and leading to the introduction of several new AEDs, among which is oxcarbazepine (Trileptal). This 10-ketoanalogue of carbamazepine seems to be a weaker inducer of cytochrome P450 3A4. However, pharmacokinetic interactions with clinical significance have already been reported, before the marketing of Trileptal in France. The aim of this study was to develop and validate a HPLC method allowing simultaneous dosage of oxcarbazepine, 10-hydroxycarbamazepine, epoxycarbamazepine, carbamazepine, phenobarbital and phenytoïn. After plasma defecation by acetonitrile, dosage was obtained by analysis of the supernatants on a C(18) reversed-phase column coupled with UV detection (240 nm). The statistical validation was performed according to the recommendations of a European technical commission. This method seems to provide a quite good selectivity from the psychotropic therapeutics, which is commonly coprescribed with AEDs. Linearity was established for the whole concentration range, whatever the compound. Quantization limits of oxcarbazepine, 10-hydroxycarbamazepine, epoxycarbamazepine, carbamazepine, phenobarbital and phenytoïn are 0.58, 3.5, 2.35, 0.66, 1.02 and 3.13 microg/ml, respectively, and absolute recoveries are 105.15, 84.76, 94.45, 96.52, 98.62 and 95.08%, respectively.

The importance of drug interactions in epilepsy therapy

Long-term antiepileptic drug (AED) therapy is the reality for the majority of patients diagnosed with epilepsy. One AED will usually be sufficient to control seizures effectively, but a significant proportion of patients will need to receive a multiple AED regimen. Furthermore, polytherapy may be necessary for the treatment of concomitant disease. The fact that over-the-counter drugs and nutritional supplements are increasingly being self-administered by patients also must be considered. Therefore the probability of patients with epilepsy experiencing drug interactions is high, particularly with the traditional AEDs, which are highly prone to drug interactions. Physicians prescribing AEDs to patients with epilepsy must, therefore, be aware of the potential for drug interactions and the effects (pharmacokinetic and pharmacodynamic) that can occur both during combination therapy and on drug discontinuation. Although pharmacokinetic interactions are numerous and well described, pharmacodynamic interactions are few and usually concluded by default. Perhaps the most clinically significant pharmacodynamic interaction is that of lamotrigine (LTG) and valproic acid (VPA); these drugs exhibit synergistic efficacy when coadministered in patients with refractory partial and generalised seizures. Hepatic metabolism is often the target for pharmacokinetic drug interactions, and enzyme-inducing drugs such as phenytoin (PHT), phenobarbitone (PB), and carbamazepine (CBZ) will readily enhance the metabolism of other AEDs [e.g., LTG, topiramate (TPM), and tiagabine (TGB)]. The enzyme-inducing AEDs also enhance the metabolism of many other drugs (e.g., oral contraceptives, antidepressants, and warfarin) so that therapeutic efficacy of coadministered drugs is lost unless the dosage is increased. VPA inhibits the metabolism of PB and LTG, resulting in an elevation in the plasma concentrations of the inhibited drugs and consequently an increased risk of toxicity. The inhibition of the metabolism of CBZ by VPA results in an elevation of the metabolite CBZ-epoxide, which also increases the risk of toxicity. Other examples include the inhibition of PHT and CBZ metabolism by cimetidine and CBZ metabolism by erythromycin. In recent years, a more rational approach has been taken with regard to metabolic drug interactions because of our enhanced understanding of the cytochrome P450 system that is responsible for the metabolism of many drugs, including AEDs. The review briefly discusses the mechanisms of drug interactions and then proceeds to highlight some of the more clinically relevant drug interactions between AEDs and between AEDs and non-AEDs. Understanding the fundamental principles that contribute to a drug interaction may help the physician to better anticipate a drug interaction and allow a graded and planned therapeutic response and, therefore, help to enhance the management of patients with epilepsy who may require treatment with polytherapy regimens.

Simultaneous determination of four antiepileptic drugs in serum by high-performance liquid chromatography

A high-performance liquid chromatographic method has been developed for the simultaneous determination of oxcarbazepine, 10-hydroxycarbamazepine, epoxycarbamazepine, carbamazepine, phenobarbital and phenytoin. After protein precipitation by acetonitrile, the supernatant was analysed on a C18 reversed-phase HPLC column. Antiepileptic drugs and oxazepam (internal standard) were detected by ultraviolet absorbance at 240 nm. Linearity was established for the whole concentration range for each compound. Quantitation limits of oxcarbazepine, 10-hydroxycarbamazepine, epoxycarbamazepine, carbamazepine, phenobarbital and phenytoin were 0.58, 3.5, 2.35, 0.66, 1.02 and 3.13 microg/mL, respectively, and mean recoveries added to serum were 105.15, 84.76, 94, 45, 96.52, 98.62 and 95.08%, respectively. This method has been used for the simultaneous determination of steady-state serum concentration of antiepileptic drugs in patients treated by one or more anticonvulsive treatment.

Oxcarbazepine in the treatment of epilepsy

Oxcarbazepine is a new antiepileptic drug (AED) that has been registered in more than 50 countries worldwide since 1990 and recently received approval in the United States and the European Union. Oxcarbazepine is a keto analog of carbamazepine and has a more favorable pharmacokinetic profile. It is rapidly absorbed after oral administration and undergoes rapid and almost complete reductive metabolism to form the pharmacologically active 10-monohydroxy derivative. Oxcarbazepine exhibits linear pharmacokinetics, no autoinduction, and minimal interaction with other AEDs. Ten controlled trials demonstrated that oxcarbazepine is safe and efficacious in the treatment of partial seizures across a wide range of ages (children to adults), situations (recent onset to treatment-resistant epilepsy), and uses (monotherapy and adjunctive therapy). The most common treatment-emergent adverse events are related to the central nervous system. Treatment-emergent hyponatremia (defined as serum sodium level < 125 mEq/L) occurred in 3% of patients treated with oxcarbazepine in clinical trials. According to the efficacy and safety profile established in the controlled trials, oxcarbazepine represents an important new treatment option indicated for monotherapy and adjunctive therapy in adults with partial seizures and as adjunctive therapy in children aged 4 years or older with partial seizures. Although structurally similar to carbamazepine, significant differences exist in the pharmacokinetics, drug interaction potential, adverse-effect profile, and dosage and titration between these two agents, and they should be considered distinct therapeutic agents.

Efficacy, pharmacology, and adverse effects of antiepileptic drugs

This article discusses the factors involved in the appropriate selection of anticonvulsant medications. The clinical use of commonly used traditional antiepileptic drugs and the newly marketed antiepileptic drugs is discussed. This includes the specific indications for use, adverse effects, and dosing of each drug. Drug interactions, mechanisms of action, and pharmacological properties of each drug is also reviewed.

Antiepileptic drug interactions

This article reviews the potential interactions of antiepileptic drugs (AEDs) and the pharmacokinetic and pharmacodynamic principles involved. It describes the absorptive and distributive properties of AEDs and the effects on protein binding, hepatic metabolism, and elimination resulting from co-administration of AEDs with food or other drugs. Drug behavior is a function of absorption, metabolism, distribution, and elimination. Administration of either multiple AEDs or a combination of AEDs plus drugs for other conditions can modify any of these physiologic processes, possibly resulting in complex interactions. These may include alterations in the bio-availability and absorption of a drug and changes in half-life and serum level through induction or inhibition of hepatic metabolism. In most cases, increases or decreases in serum concentrations will signal a drug interaction. In other cases, clinically significant drug interactions remain undetected owing to apparently stable serum concentrations. Co-administration of drugs may affect the rate of clearance of one or both drugs. The effect on clearance varies, owing to genetic factors, patient characteristics (age and presence of co-morbidities), and individual responses. AEDs that induce hepatic metabolism can also influence the metabolism of concomitantly administered non-epilepsy medications and can interfere with oral contraceptives, as well as vitamins D and K. Patients with renal insufficiency or advanced age may experience incomplete renal excretion and should receive reduced dosages of drug. Understanding the pharmacokinetics and pharmacodynamic properties of AEDs and the route of metabolism of all competing drugs is important for optimal management of patients with epilepsy and for prevention of avoidable drug interactions.

Epilepsy

The successful management of epilepsy requires a thorough and individualized approach that accurately establishes the patient's seizure type(s) and, when appropriate, epilepsy syndrome. Selection of pharmacologic and nonpharmacologic therapy should be rational and tailored to each patient. In this manner, clinicians are able to take advantage of new treatments to minimize the impact of seizures, treatment side effects, and epilepsy-related psychosocial difficulties on their patients, thereby enabling them to function in society at the highest possible level.

Progress report on new antiepileptic drugs: a summary of the Fifth Eilat Conference (EILAT V)

The Fifth Eilat Conference on New Antiepileptic Drugs (AEDs) took place at the Dan Hotel, Eilat, Israel, 25-29 June 2000. Basic scientists, clinical pharmacologists and neurologists from 20 countries attended the conference, whose main themes included recognition of unexpected adverse effects, new indications of AEDs, and patient-tailored AED therapy. According to tradition, the central part of the conference was devoted to a review of AEDs in development, as well to updates on AEDs that have been marketed in recent years. This article summarizes the information presented on drugs in preclinical and clinical development, including AWD 131-138, DP-valproate, harkoseride, LY300164, NPS 1776, NW 1015, pregabalin, remacemide, retigabine, rufinamide and valrocemide. The potential value of an innovative strategy, porcine embryonic GABAergic cell transplants, is also discussed. Finally, updates on felbamate, fosphenytoin, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, vigabatrin, zonisamide, and the antiepileptic vagal stimulator device are presented.

Oxcarbazepine for Treatment of Partial Epilepsy: A Review and Recommendations for Clinical Use

Recent trials and extensive postmarketing use confirm the efficacy and safety of oxcarbazepine (OXC) as a first-line treatment for adults and children with simple partial seizures, complex partial seizures, and partial seizures evolving to secondarily generalized seizures. OXC undergoes reductive metabolism at its keto moiety to form 10-hydroxy-10,11-dihydro-10-oxo-5H-dibenz[b,f]azepine-5-carboxamide (MHD), which is glucuronidated and excreted in the urine, with minimal involvement of the hepatic cytochrome P450-dependent enzymes. OXC has some drug interactions, and does not require titration, allowing for better tolerability. Titration for monotherapy and adjunctive therapy of OXC could begin at 150 mg/day and be increased by 150 mg every 2-3 days until the target dose of 900-1200 mg/day is reached. If necessary, one can go faster and start with up to 600 mg/day and titrate with weekly increments up to 600 mg/day if necessary for seizure control. Conversion to monotherapy can be done overnight or gradually. For gradual conversion, use the recommended titration of OXC and withdraw the baseline antiepileptic drugs gradually by 25%, starting at Day 14 or earlier in case of baseline tolerability issues. Consider reducing the dose of the primary antiepileptic drug during adjunctive therapy in case of adverse events or increase the dose of OXC in case of incomplete seizure control. In children OXC should be started at 8-10 mg/kg/day in two or three divided doses. If clinically indicated the dose can then be increased by 10 mg/kg/day in weekly intervals with final doses up to 30-46 mg/kg/day. Dose adjustment may be necessary in very young children (age 2-5 years) and in patients with renal dysfunction, based on renal clearance. However no adjustment of OXC dose is needed in patients with mild to moderate hepatic dysfunction. OXC has a number of advantages which include rapid titration, no need for safety monitoring (except for uncommon and mostly asymptomatic hyponatremia), a low potential for drug-drug interactions (except for those possibly impairing the effectiveness of oral contraceptives and increasing the serum concentration of phenytoin), a rash rate of less than 5%, similar efficacy and similar or better tolerability and safety compared with first-generation antiepileptic drugs. OXC is a valuable alternative to current treatment options.

Comparative stereoselective pharmacokinetic analysis of 10-hydroxycarbazepine after oral administration of its individual enantiomers and the racemic mixture to dogs

PURPOSE

10-hydroxycarbazepine (MHD) is the active metabolite of the new antiepileptic drug oxcarbazepine. MHD is a chiral molecule with an asymmetric carbon at position 10. The purpose of this study was to evaluate the stereoselectivity in the pharmacokinetics of the enantiomers of MHD after oral administration of the individual MHD enantiomers and the racemic mixture to dogs.

METHODS

A racemic mixture of MHD and the individual MHD enantiomers were administered to six dogs in a crossover design. Plasma and urine concentrations of R(-)- and S(+)-MHD were determined by a stereoselective high-performance liquid chromatography assay.

RESULTS

The area under the concentration-time curve of R(-)-MHD was significantly greater than that of S(+)-MHD after the administration of the individual enantiomers but not after the administration of MHD in a racemic form. The formation clearance of the S(+)-MHD glucuronide was approximately three times greater than that of R(-)-MHD glucuronide. No difference was found in the renal clearance and protein binding of R(-)- and S(+)-MHD enantiomers.

CONCLUSIONS

The pharmacokinetics of the MHD enantiomers was found to be stereoselective, mainly as a result of the stereoselectivity in the glucuronidation process. The difference in the pharmacokinetic parameters found after administration of individual MHD enantiomers compared with the administration of MHD in a racemic form suggests the possibility of interaction between the two enantiomers. Stereoselective pharmacokinetic and pharmacodynamic studies are needed to evaluate the rationale of developing MHD as a new antiepileptic drug, either in a stereospecific or racemic form.

Plasma level monitoring of oxcarbazepine in epileptic patients

BACKGROUND

Despite the wide use of oxcarbazepine (OXC) there is little data concerning the usefulness of plasma level monitoring with this drug in Mexican patients with epilepsy. The purpose of the present study was to determine whether OXC levels correlate with dose, age, weight, or drugs used concomitantly.

METHODS

Plasma levels of the antiepileptic drug OXC were evaluated in 214 patients with epilepsy. In each patient, plasma MHD (10-hydroxycarbazepine, the main metabolite of OXC) concentration was determined. Additionally, plasma protein binding was determined in 30 patients and affinity to red blood cells (RBCs) was evaluated in 50 patients.

RESULTS

Our results showed that the mean plasma level of MHD was 15.34 microg/mL, mean protein binding ranged between 30-40%, and the mean RBC concentration was 18.38 microg/mL. A relationship between dose/weight and plasma concentration was found (r = 0.5149, p <0.001). In addition, a linear relationship between plasma and RBC concentration was established (r = 0.8806, p <0.0001).

CONCLUSIONS

These results suggest that for OXC, routine RBC concentrations are not necessary to make drug adjustments.

The clinical pharmacokinetics of the new antiepileptic drugs

Because pharmacokinetics is a major determinant of the magnitude and duration of pharmacologic response, understanding the kinetic properties of the new antiepileptic drugs (AEDs) is essential for the correct use of these compounds in clinical practice. After oral administration, absorption is rapid and relatively efficient for the new AEDs, the most notable exception being gabapentin, whose bioavailability decreases with increasing dosage. None of the new AEDs is extensively bound to plasma proteins except for tiagabine, which is over 95% protein-bound. The route of elimination differs to an important extent from one compound to another, and elimination half-lives range from over 30 h for zonisamide to 5-7 h for gabapentin. For all drugs that are metabolized, half-life is shortened and clearance is increased when patients receive concomitant enzyme-inducing agents such as barbiturates, phenytoin, and carbamazepine. Lamotrigine metabolism is markedly inhibited by valproic acid, and felbamate may increase the serum levels of most other AEDs. Felbamate, topiramate, and oxcarbazepine may also reduce the efficacy of the contraceptive pill by stimulating its metabolism.

Oxcarbazepine

The success of carbamazepine (CBZ) as a broad-spectrum antiepileptic drug (AED) has led to its use as first-line therapy in children and adults for partial and generalized tonic-clonic seizures. The limitations of CBZ include toxicity in sensitive individuals, autoinduction, which requires dose adjustment when therapy is initiated, and chronic hepatic induction, producing drug interactions when CBZ is used with AEDs and other drugs that undergo hepatic metabolism. One of two main products of CBZ microsomal metabolism, CBZ-10,11-epoxide (formed by oxidation of the double bond between C-10 and C-11), appears to provide antiepileptic efficacy but contributes significantly to clinical toxicity. The most common adverse effects of CBZ are central nervous system (CNS) symptoms, followed by gastrointestinal, hepatic, endocrine disturbances, and teratogenic effects. Oxcarbazepine (OXC) was developed to provide a compound chemically similar enough to CBZ to mimic its efficacy and overall safety while improving its side-effect profile. Biotransformation of OXC does not involve formation of an epoxide metabolite. Compared with the parent compound, hepatic microsomal enzyme induction and autoinduction are greatly reduced. The clinical efficacy of OXC compares favorably with CBZ in clinical trials. Clinical development of OXC began in Europe. Results of Phase I trials started to appear in the early 1980s. Controlled clinical trials, reported in the mid- to late 1980s, led to approval of OXC in many European countries, and now in over 50 nations around the world. United States multicenter clinical trials have recently been completed, and at this writing the drug is awaiting approval by the FDA. This article reviews the pharmacology, animal data, outcomes of published controlled clinical trials, postmarketing data, adverse experiences, and current recommendations for clinical use of OXC.

Metabolism of some "second"- and "fourth"-generation antidepressants: iprindole, viloxazine, bupropion, mianserin, maprotiline, trazodone, nefazodone, and venlafaxine

1. This review summarizes the major known aspects of the metabolism of second-generation (iprindole, viloxazine, bupropion, mianserin, maprotiline, and trazodone) and fourth-generation (nefazodone and venlafaxine) antidepressants. 2. Discussions about specific enzymes involved and about possible pharmacokinetic drug-drug interactions, particularly as they relate to cytochrome P450 enzymes, are provided.

Metabolism and excretion of mood stabilizers and new anticonvulsants

1. The mood stabilizers lithium, carbamazepine (CBZ), and valproate (VPA), have differing pharmacokinetics, structures, mechanisms of action, efficacy spectra, and adverse effects. Lithium has a low therapeutic index and is renally excreted and hence has renally-mediated but not hepatically-mediated drug-drug interactions. 2. CBZ has multiple problematic drug-drug interactions due to its low therapeutic index, metabolism primarily by a single isoform (CYP3A3/4), active epoxide metabolite, susceptibility to CYP3A3/4 or epoxide hydrolase inhibitors, and ability to induce drug metabolism (via both cytochrome P450 oxidation and conjugation). In contrast, VPA has less prominent neurotoxicity and three principal metabolic pathways, rendering it less susceptible to toxicity due to inhibition of its metabolism. However, VPA can increase plasma concentrations of some drugs by inhibiting metabolism and increase free fractions of certain medications by displacing them from plasma proteins. 3. Older anticonvulsants such as phenobarbital and phenytoin induce hepatic metabolism, may produce toxicity due to inhibition of their metabolism, and have not gained general acceptance in the treatment of primary psychiatric disorders. 4. The newer anticonvulsants felbamate, lamotrigine, topiramate, and tiagabine have different hepatically-mediated drug-drug interactions, while the renally excreted gabapentin lacks hepatic drug-drug interactions but may have reduced bioavailability at higher doses. 5. Investigational anticonvulsants such as oxcarbazepine, vigabatrin, and zonisamide appear to have improved pharmacokinetic profiles compared to older agents. 6. Thus, several of the newer anticonvulsants lack the problematic drug-drug interactions seen with older agents, and some may even (based on their mechanisms of action and preliminary preclinical and clinical data) ultimately prove to have novel psychotropic effects.

Best practice guidelines for the management of women with epilepsy. The Women with Epilepsy Guidelines Development Group

Clinical guidelines for the treatment of epilepsy have been published. A statement on management issues for women with epilepsy has recently been produced by the American Academy of Neurology which has raised awareness of the issues facing women with epilepsy. The communication presented here aims to review current literature on specific issues relating to women with epilepsy, and proposes graded recommendations for its management within a UK health care framework.