Absence of interaction between oxcarbazepine and erythromycin

Seizures as adverse events of antibiotic drugs: A systematic review

OBJECTIVE

Antibiotic drugs are commonly associated with seizures. Tailoring antibiotics to the individual risk for seizures is challenged as avoidance of certain antibiotic classes may no longer be possible due to the emergence of resistant bacteria. We performed a systematic review regarding the current evidence for seizures associated with all antibiotic classes, their underlying mechanisms, and predisposing factors.

METHODS

The medical search engine PubMed was systematically screened to identify articles in English published between 1960 and 2013. All study designs were considered and evidence was assessed.

RESULTS

We included 143 articles involving 25,712 patients and 25 different antibiotics. Evidence for antibiotic-related symptomatic seizures is low to very low, mainly deriving from studies regarding β-lactams, especially unsubstituted penicillins and fourth-generation cephalosporins, as well as carbapenems, mainly imipenem, all administered in high doses or in patients with renal dysfunction, brain lesions, or known epilepsy. Evidence regarding symptomatic seizures from fluoroquinolones only relies on case reports and case series with most reports for ciprofloxacin in patients with renal dysfunction, mental disorders, prior seizures, or coadministered theophylline.

CONCLUSIONS

Evidence for an association between antibiotic drugs and symptomatic seizures is low to very low (evidence Class III-IV). Despite this, numerous reports point to an increased risk for symptomatic seizures especially of unsubstituted penicillins, fourth-generation cephalosporins, imipenem, and ciprofloxacin in combination with renal dysfunction, brain lesions, and epilepsy. During administration of such antibiotics in patients with particular predispositions, close monitoring of serum levels is advocated. As most seizures associated with cephalosporins are nonconvulsive, continuous EEG should be considered in patients with altered levels of consciousness.

Pharmacokinetic drug interactions of antimicrobial drugs: a systematic review on oxazolidinones, rifamycines, macrolides, fluoroquinolones, and Beta-lactams

Like any other drug, antimicrobial drugs are prone to pharmacokinetic drug interactions. These drug interactions are a major concern in clinical practice as they may have an effect on efficacy and toxicity. This article provides an overview of all published pharmacokinetic studies on drug interactions of the commonly prescribed antimicrobial drugs oxazolidinones, rifamycines, macrolides, fluoroquinolones, and beta-lactams, focusing on systematic research. We describe drug-food and drug-drug interaction studies in humans, affecting antimicrobial drugs as well as concomitantly administered drugs. Since knowledge about mechanisms is of paramount importance for adequate management of drug interactions, the most plausible underlying mechanism of the drug interaction is provided when available. This overview can be used in daily practice to support the management of pharmacokinetic drug interactions of antimicrobial drugs.

Modern methods for analysis of antiepileptic drugs in the biological fluids for pharmacokinetics, bioequivalence and therapeutic drug monitoring

Epilepsy is a chronic disease occurring in approximately 1.0% of the world's population. About 30% of the epileptic patients treated with availably antiepileptic drugs (AEDs) continue to have seizures and are considered therapy-resistant or refractory patients. The ultimate goal for the use of AEDs is complete cessation of seizures without side effects. Because of a narrow therapeutic index of AEDs, a complete understanding of its clinical pharmacokinetics is essential for understanding of the pharmacodynamics of these drugs. These drug concentrations in biological fluids serve as surrogate markers and can be used to guide or target drug dosing. Because early studies demonstrated clinical and/or electroencephalographic correlations with serum concentrations of several AEDs, It has been almost 50 years since clinicians started using plasma concentrations of AEDs to optimize pharmacotherapy in patients with epilepsy. Therefore, validated analytical method for concentrations of AEDs in biological fluids is a necessity in order to explore pharmacokinetics, bioequivalence and TDM in various clinical situations. There are hundreds of published articles on the analysis of specific AEDs by a wide variety of analytical methods in biological samples have appears over the past decade. This review intends to provide an updated, concise overview on the modern method development for monitoring AEDs for pharmacokinetic studies, bioequivalence and therapeutic drug monitoring.

Comments on the Eslicarbazepine Acetate Section of the Article ‘Therapeutic Drug Monitoring of the Newer Anti-Epilepsy Medications’

The recent review of Matthew D. Krasowski on ‘Therapeutic Drug Monitoring of the Newer Anti-Epilepsy Medications’ is a useful foundation of comparative interpretations on our current knowledge about therapeutic drug monitoring. Within the review, the statement that therapeutic drug monitoring has a minimal role in the therapeutic use of eslicarbazepine acetate due to its relatively predictable pharmacokinetics reflects the existing body of evidence although some information such as eslicarbazepine acetate’s chemical structure, proportions of its metabolites, their pharmacokinetics and chiral method of plasma level measurement need to be revised. These critical characteristics differentiate the novel compound from former dibenzazepines such as carbamazepine and oxcarbazepine in its clinical effects and needs for therapeutic drug monitoring.

A new look at the second-generation antiepileptic drugs: a decade of experience

OBJECTIVE

To review data from the literature regarding the efficacy and tolerability of the second-generation antiepileptic drugs which were approved by the Food and Drug Administration (FDA) since 1994.

METHODS

A MEDLINE search of the literature, as well as review of bibliographies, was performed to identify randomized controlled trials and other reports evaluating efficacy, pharmacokinetic profile, adverse effects, and drug interactions of the second-generation antiepileptic drugs. Key search terms included felbamate, gabapentin, lamotrigine, topiramate, tiagabine, levetiracetam, oxcarbazepine, zonisamide, and pregabalin.

RESULTS

Each of the second-generation antiepileptic drugs has demonstrated statistically significant reductions in seizure frequency over baseline compared with placebo or active control. Limited studies of efficacy of the new agents compared with the traditional antiepileptic drugs found no significant differences. Each of the second-generation antiepileptic drugs has a unique pharmacokinetic and side-effect profile. Compared with the traditional agents, the second-generation antiepileptic drugs have fewer serious adverse effects, as well as drug interactions.

CONCLUSION

Knowledge of the second-generation antiepileptic drugs has greatly expanded over the past decade. The newer agents offer many options in the treatment of epilepsy that are safe, efficacious, and well tolerated.

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.

Lack of pharmacokinetic interaction between oxcarbazepine and lamotrigine

Epilepsy and bipolar disorder are commonly treated by combination drug therapy, such as lamotrigine and oxcarbazepine. To ensure the safety of this combination, information on pharmacokinetics and tolerability must be available. The objective of study was to evaluate the pharmacokinetics and tolerability of coadministered lamotrigine and oxcarbazepine in healthy subjects. This randomized, single-blind, parallel-group study comprised three cohorts: lamotrigine (200 mg daily) plus oxcarbazepine (600 mg twice daily), lamotrigine (200 mg daily) plus placebo, and oxcarbazepine (600 mg twice daily) plus placebo. Serial blood samples were collected at steady state to determine serum concentrations of lamotrigine and plasma concentrations of oxcarbazepine and its active metabolite 10-monohydroxy metabolite (MHD). Pharmacokinetic parameters were determined by noncompartmental methods. Tolerability was monitored through adverse event reports, clinical laboratory results, vital signs, and electrocardiograms. A total of 47 male volunteers received study drugs. At steady state, lamotrigine AUC((0-24)) and C(max) were not significantly affected by oxcarbazepine co-therapy, nor were MHD AUC((0-12)) and C(max) significantly affected by lamotrigine co-therapy. The most common adverse events, headache, dizziness, nausea, and somnolence, occurred more frequently during lamotrigine and oxcarbazepine combination therapy than during the monotherapy. No significant changes in clinical laboratory parameters, vital signs, or electrocardiograms were reported. In conclusion, the combination of lamotrigine and oxcarbazepine does not require dose adjustments based on pharmacokinetic data. However, it is important to recognize that the combination therapy was associated with more frequent adverse events.

Oxcarbazepine: current status and clinical applications

Oxcarbazepine (OXC) was introduced in 1990 and is now registered in 54 countries worldwide as monotherapy, as add-on treatment for partial seizures, with or without secondarily generalised seizures, and primary generalised tonic-clonic seizures. OXC and its active metabolite, monohydroxy derivative (MHD), block voltage-dependent sodium channels and may effect potassium and calcium channels. In animal models of epilepsy, OXC and MHD have efficacy similar to that of CBZ. There is no evidence for clinically important teratogenicity, mutagenicity or carcinogenicity. OXC has no effect on serum concentrations of hepatically metabolised anti-epileptic drugs (AEDs) and no clinically important interactions with common non-AEDs, other than hormonal contraceptives. MHD has low protein binding and linear pharmacokinetics. Adverse effects (AEs) are usually related to the central nervous system. Approximately three-quarters of patients who experience adverse effects with CBZ improve when switched to OXC, without loss of seizure control. The incidence of rash appears to be less than that expected with CBZ. While hyponatraemia may occur more often with OXC than with CBZ, it is rarely symptomatic. OXC is an effective and safe drug for the treatment of partial-onset and primary generalised tonic-clonic seizures. Placebo- and low-dose controlled double-blind monotherapy studies prove that OXC has anticonvulsant activity and that therapeutic dosages may be obtained with a 24 h titration in hospitalised patients, if necessary. Comparative double-blind trials show that OXC has similar efficacy to VPA, CBZ and PHT, but has advantages compared to those agents in terms of pharmacokinetics, side-effects and tolerability.

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.

Oxcarbazepine: Efficacy, safety, and tolerability in the treatment of mania

A twelve-week study examined the efficacy, safety, and tolerability of oxcarbazepine in the treatment of mania. Twenty male subjects, all of whom were stable on valproic acid, qualified for the study. The conversion from valproic acid to oxcarbazepine was completed over a three-week period. Scores from the BPRS, CGI and SAJEE-GI were collected and analyzed. The results of the study supported the efficacy, safety, and tolerability of oxcarbazepine for the treatment of mania. Another potential advantage of oxcarbazepine is a metabolic pathway that may reduce drug interactions. Qnt] Psych Can Pract 2004; 8: 37-40).

Overview of the Clinical Pharmacokinetics of Oxcarbazepine

Oxcarbazepine (GP 47680, 10,11-dihydro-10-oxo-5H-dibenz[b,f]azepine- 5-carboxamide) is an antiepileptic drug registered worldwide by Novartis under the trade name Trileptal((R)). Trileptal((R))is approved as adjunctive therapy or monotherapy for the treatment of partial seizures in adults and in children. In the US, Trileptal((R)) is approved as adjunctive therapy in adults and in children >/=4 years of age and as monotherapy in adults and in children.Trileptal((R))is currently marketed as 150, 300 and 600mg film-coated tablets for oral administration. A 60 mg/mL (6%) oral suspension formulation has also been registered worldwide.Oxcarbazepine and its pharmacologically active metabolite, 10-monohydroxy derivative (MHD; 10,11-dihydro-10-hydro-carbamazepine; GP 47779) show potent antiepileptic activity in animal models comparable to that of carbamazepine (Tegretol((R))) and phenytoin. Oxcarbazepine and MHD have been shown to exert antiepileptic activity by blockade of voltage-dependent sodium channels in the brain.Oxcarbazepine is rapidly reduced by cytosolic enzymes in the liver to MHD, which is responsible for the pharmacological effect of the drug. This step is mediated by cytosolic arylketone reductases. MHD is eliminated by conjugation with glucuronic acid. Minor amounts (4% of the dose) are oxidised to the pharmacologically inactive dihydroxy derivative (DHD). The absorption of oxcarbazepine is complete. In plasma after a single oral administration of oxcarbazepine the mean apparent elimination half-life (t((1/2))) of MHD in adults was 8-9h. Food has no effect on the bioavailability of the highest strength of the final market image tablet (600mg). At steady state MHD displays predictable linear pharmacokinetics at doses ranging from 300 to 2400mg. In children with normal renal function, renal clearance of MHD is higher than in adults, with a corresponding reduction in the terminal t((1/2)) of MHD. Consequently, although no special dose recommendation is needed, an increase in the dose of oxcarbazepine may be necessary to achieve similar plasma levels to those in adults. In patients with moderate to severe renal impairment (creatinine clearance <30 mL/min), the elimination t((1/2)) of MHD is prolonged with a corresponding 2-fold increase in area under the concentration-time curve. Therefore, a dose reduction of at least 50% and a prolongation of the titration period is necessary in these patients. Mild-to-moderate hepatic impairment does not affect the pharmacokinetics of MHD. Based on in vitro and in vivo findings and compared with antiepileptic drugs such as carbamazepine, phenytoin and phenobarbital, oxcarbazepine has a low propensity for drug-drug interactions. In vitro, MHD inhibits the cytochrome P450 (CYP) 2C19 (ki [inhibition constant] = 88 micromol/L). At oxcarbazepine doses above 1.2g, a 40% increase in the concentration of phenytoin and a 15% increase in phenobarbital levels were observed. Oxcarbazepine/MHD at high doses may slightly increase phenobarbital and phenytoin plasma concentrations. Therefore, when using high doses of oxcarbazepine an adjustment in the dose of phenytoin may be required. In vitro, MHD is only a weak inducer of uridine diphospate (UDP)-glucuronyltransferase (UDPGT) and therefore is unlikely to have an effect on drugs that are mainly eliminated by conjugation through the UDPGT enzymes (e.g. valproic acid and lamotrigine). Weak interactions between MHD and antiepileptic drugs that are strong inducers of CYP enzymes have been identified. Carbamazepine, phenobarbital and phenytoin have been shown to reduce MHD levels by 30-40% when coadministered with oxcarbazepine, with no decrease in efficacy. Oxcarbazepine decreases the plasma hormone levels (ethinylestradiol and levonorgestrel) of oral contraceptives and may therefore have the potential to cause oral contraception failure.

Oxcarbazepine: a review of its use in children with epilepsy

Oxcarbazepine (Trileptal, Timox) is structurally related to carbamazepine and has anticonvulsant activity. Studies suggest that the anticonvulsant activity of oxcarbazepine is mediated via the blocking of neuronal ion channels. In patients aged <18 years, the efficacy of oxcarbazepine monotherapy was similar to that of phenytoin in children with partial onset or generalized tonic-clonic seizures in a 48-week trial. Additional supporting findings demonstrated that 43-71% of patients with partial onset, generalized or undetermined epilepsy were seizure free after oxcarbazepine monotherapy (mean dosage 27.7-50 mg/kg/day; duration 1-5 years). In contrast, one small nonblind trial showed more patients treated with oxcarbazepine monotherapy than with carbamazepine monotherapy had recurrent seizures during 16 months of therapy (although the conclusions that can be drawn from this trial are limited). As adjunctive therapy, oxcarbazepine was significantly better than placebo at reducing seizure frequency in children and adolescents with refractory partial onset seizures with or without secondary generalization: the median percentage change in partial onset seizure frequency was 35% vs 9%, respectively, during 16 weeks of therapy. In noncomparative trials of adjunctive oxcarbazepine (mean dosage of 34.5-56.7 mg/kg/day), 7-11% of patients with partial onset or generalized seizures were seizure free during treatment, and 20-54% had seizure reductions of > or=50%. Oxcarbazepine was generally well tolerated during monotherapy and adjunctive therapy; 2.5% and 10% of patients withdrew from well controlled trials of oxcarbazepine monotherapy and adjunctive therapy. Oxcarbazepine monotherapy was better tolerated than phenytoin and events observed in oxcarbazepine-treated patients were transient. Oxcarbazepine metabolism is largely unaffected by induction of the cytochrome (CYP) P450 system. However, oxcarbazepine can inhibit CYP2C19 and induce CYP3A4 and CYP3A5, thereby interfering with the metabolism of other drugs (e.g. phenytoin). In addition, oxcarbazepine decreases plasma levels of oral contraceptives and alternative contraceptive methods should be used. In conclusion, oxcarbazepine (as both monotherapy and adjunctive therapy) has shown efficacy in the treatment of partial onset seizures in children with epilepsy. Nevertheless, the generally favorable tolerability profile and relatively low potential for drug interactions of oxcarbazepine make it a valuable option in the treatment of childhood epilepsy.

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.

Clinically important drug interactions in epilepsy: interactions between antiepileptic drugs and other drugs

Antiepileptic drugs (AEDs) are commonly prescribed for long periods, up to a lifetime, and many patients will require treatment with other agents for the management of concomitant or intercurrent conditions. When two or more drugs are prescribed together, clinically important interactions can occur. Among old-generation AEDs, carbamazepine, phenytoin, phenobarbital, and primidone are potent inducers of hepatic enzymes, and decrease the plasma concentration of many psychotropic, immunosuppressant, antineoplastic, antimicrobial, and cardiovascular drugs, as well as oral contraceptive steroids. Most new generation AEDs do not have clinically important enzyme inducing effects. Other drugs can affect the pharmacokinetics of AEDs; examples include the stimulation of lamotrigine metabolism by oral contraceptive steroids and the inhibition of carbamazepine metabolism by certain macrolide antibiotics, antifungals, verapamil, diltiazem, and isoniazid. Careful monitoring of clinical response is recommended whenever a drug is added or removed from a patient's AED regimen.

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.

New antiepileptic drugs: review on drug interactions

During the Past decade, nine new antiepileptic drugs (AEDs) namely, Felbamate, Gabapentin, Levetiracetam, Lamotrigine, Oxcarbazepine, Tiagabine, Topiramate, Vigabatrin and Zonisamide have been marketed worldwide. The introduction of these drugs increased appreciably the number of therapeutic combinations used in the treatment of epilepsy and with it, the risk of drug interactions. In general, these newer antiepileptic drugs exhibit a lower potential for drug interactions than the classic AEDs, like phenytoin, carbamazepine and valproic acid, mostly because of their pharmacokinetic characteristics. For example, vigabatrin, levetiracetam and gabapentin, exhibit few or no interactions with other AEDs. Felbamate, tiagabine, topiramate and zonisamide are sensitive to induction by known anticonvulsants with inducing effects but are less vulnerable to inhibition by common drug inhibitors. Felbamate, topiramate and oxcarbazepine are mild inducers and may affect the disposition of oral contraceptives with a risk of failure of contraception. These drugs also inhibit CYP2C19 and may affect the disposition of phenytoin. Lamotrigine is eliminated mostly by glucuronidation and is susceptible to inhibition by valproic acid and induction by classic AEDs such as phenytoin, carbamazepine, phenobarbital and primidone.

Oxcarbazepine

Oxcarbazepine is one of the recently introduced anti-epileptic drugs (AEDs) in the US. This drug has demonstrated efficacy as adjunctive therapy in adults and children, and as monotherapy in adults for the treatment of seizures of partial onset. There is also convincing evidence of its efficacy in patients with newly diagnosed and refractory trigeminal neuralgia. In addition, the initial efficacy results of oxcarbazepine in other neuropathic pain conditions and in bipolar disorders are encouraging. In this review, recommendations on the optimal clinical use of oxcarbazepine are given based on its pharmacokinetic profile, efficacy and tolerability in those various conditions.

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.

Pharmacologic management of epilepsy in the elderly

OBJECTIVE

To review the epidemiology and pharmacologic management of epilepsy in elderly patients.

DATA SOURCES

Controlled trials, case studies, and review articles identified via MEDLINE using the search terms epilepsy, seizures, elderly, phenobarbital, primidone, phenytoin, carbamazepine, valproic acid, felbamate, gabapentin, lamotrigine, topiramate, tiagabine, levetiracetam, oxcarbazepine, and zonisamide. Recently published standard textbooks on epilepsy were also consulted.

DATA SYNTHESIS

Epilepsy is a common neurologic disorder in the elderly. Cerebrovascular and neurodegenerative diseases are the most common causes of new-onset seizures in these patients. Alterations in protein binding, distribution, elimination, and increased sensitivity to the pharmacodynamic effects of antiepileptic drugs (AEDs) are relatively frequent, and these factors should be assessed at the initiation, and during adjustment, of treatment. Drug-drug interactions are also an important issue in elderly patients, because multiple drug use is common and AEDs are susceptible to many interactions. In addition to understanding age-related changes in the pharmacokinetics and pharmacodynamics of AEDs, clinicians should know the common seizure types in the elderly and the spectrum of AED activity for these seizure types. AEDs with activity against both partial-onset and generalized seizures include felbamate, lamotrigine, levetiracetam, topiramate, valproic acid, and zonisamide. Other AEDs discussed in this review (carbamazepine, gabapentin, phenobarbital, phenytoin, primidone, and tiagabine) are most useful for partial-onset seizures.

CONCLUSION

The provision of safe and effective drug therapy to elderly patients requires an understanding of the unique age-related changes' in the pharmacokinetics and pharmacodynamics of AEDs as well as an appreciation of common seizure types and the drugs that are effective for the specific types seen in the elderly.

Oxcarbazepine, an antiepileptic agent

BACKGROUND

Epilepsy is a common neurologic condition. Many of the currently approved pharmacologic agents for its treatment are associated with numerous adverse drug reactions and drug interactions.

OBJECTIVE

This review describes the pharmacology and therapeutic use of oxcarbazepine, an analogue of the well-known antiepileptic agent carbamazepine.

METHODS

Articles for review were identified through a search of MEDLINE, International Pharmaceutical Abstracts, and EMBASE for the years 1980 through 2000. The terms used individually and in combination were oxcarbazepine, carbamazepine, epilepsy, and seizures.

RESULTS

Oxcarbazepine and its primary metabolite have been effective in animal models of epilepsy that generally predict efficacy in generalized tonic-clonic seizures and partial seizures in humans. The exact mechanism of action of oxcarbazepine is unknown, although as with carbamazepine, it is believed to involve blockade of voltage-gated sodium channels. The pharmacokinetic profile of oxcarbazepine is less complicated than that of carbamazepine, with less metabolism by the cytochrome P450 system, no production of an epoxide metabolite, and lower plasma protein binding. The clinical efficacy and tolerability of oxcarbazepine have been demonstrated in trials in adults, children, and the elderly. In a double-blind, randomized, crossover trial in adults, oxcarbazepine 300 mg was associated with a decrease in the mean frequency of tonic seizures (21.4 vs 30.5 seizures during steady-state periods) and tonic-clonic seizures (8.2 vs 10.4) compared with carbamazepine 200 mg (P = 0.05). A multinational, multicenter, double-blind, placebo-controlled, randomized, 28-week trial assessed the efficacy and tolerability of oxcarbazepine at doses of 600, 1200, and 2400 mg as adjunctive therapy in patients with uncontrolled partial seizures. All 3 oxcarbazepine groups demonstrated a reduction in seizure frequency per 28-day period compared with placebo (600 mg, 26% reduction; 1200 mg, 40% reduction; 2400 mg, 50% reduction; placebo, 7.6% reduction; all, P < 0.001). A trial in children assessed the efficacy and toxicity of oxcarbazepine (median dose, 31.4 mg/kg/d) as adjunctive therapy for partial seizures. Patients receiving oxcarbazepine experienced a 35% reduction in seizure frequency, compared with a 9% reduction in the placebo group (P < 0.001). The most common adverse effects associated with oxcarbazepine are related to the central nervous system (eg, dizziness, headache, diplopia, and ataxia) and the gastrointestinal system (eg, nausea and vomiting). Compared with carbamazepine, there is an increased risk of hyponatremia with oxcarbazepine. The frequency and severity of drug interactions are less with oxcarbazepine than with carbamazepine or other antiepileptic agents.

CONCLUSIONS

Oxcarbazepine may be considered an appropriate alternative to carbamazepine for the treatment of partial seizures in patients who are unable to tolerate carbamazepine. Its use in nonseizure disorders remains to be examined in large-scale clinical trials, and pharmacoeconomic comparisons of oxcarbazepine with other antiepileptic agents, particularly carbamazepine, are needed.

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.

Safety and efficacy of oxcarbazepine: results of randomized, double-blind trials

Oxcarbazepine is approved as monotherapy and adjunctive therapy for partial seizures with and without secondarily generalized seizures in adults and as adjunctive therapy for partial-onset seizures in children aged 4-16 years. The clinical development of oxcarbazepine is different from the newer antiepileptic drugs (AEDs) in the extent and concordance of results across clinical trials. The safety and efficacy of oxcarbazepine was evaluated in adjunctive therapy trials, in comparative monotherapy trials with classic AEDs in adults and children with newly diagnosed epilepsy, in monotherapy therapeutic failure design trials in patients with refractory partial seizures, and in trigeminal neuralgia and affective disorder. The results of oxcarbazepine in treating epilepsy are discussed.

Enzyme induction and inhibition by new antiepileptic drugs: a review of human studies

The aim of this paper is to review a number of new antiepileptic agents (i.e. felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, vigabatrin and zonisamide) for their inducing and/or inhibitory properties in humans, mainly considering the interactions where they are involved as the cause rather than the object of such interactions. Two aspects have been particularly taken into account: the changes or absence of changes in plasma/serum concentrations of concomitant drugs and the direct or indirect evidence of induction, inhibition or lack of effect on the six major human hepatic CYP isozymes (CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A4), as well as on other CYP isozymes or enzyme systems. Felbamate clearly affects the pharmacokinetics of a number of drugs, generally increasing but also decreasing their concentrations. It induces enzymes such as CYP3A4 and inhibits enzymes such as CYP2C19 and those of the beta-oxidation pathway. Topiramate is not devoid of potential interaction properties: it decreases the plasma concentrations of ethinylestradiol, induces CYP3A4 and inhibits CYP2C19. For oxcarbazepine, no inhibitory, only inductive effects have been observed thus far. Felbamate. topiramate and oxcarbazepine may induce the metabolism of steroidal oral contraceptives. In this respect, tiagabine has been studied at a rather low dose. Pharmacodynamic or pharmacokinetic interaction seems to exist between lamotrigine and carbamazepine. Lamotrigine appears to be a weak inducer of UGTs, whereas induction of CYP3A4 seems improbable as the compound does not change the concentrations of oral contraceptives or the urinary excretion of 6beta-hydroxycortisol. Zonisamide has very peculiar pharmacokinetics and an extensive metabolism. Additional information on its enzyme inducing or inhibiting properties would be necessary, as data so far collected on its effect on the pharmacokinetics of other drugs are conflicting. Gabapentin, vigabatrin and in particular levetiracetam appear to be devoid of significant enzyme inducing or inhibiting properties.

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.

Induction of ethinylestradiol and levonorgestrel metabolism by oxcarbazepine in healthy women

PURPOSE

To evaluate the effect of oxcarbazepine (OCBZ) on the pharmacokinetic profile of steroid oral contraceptives.

METHODS

Twenty-two healthy women aged 18-44 years were recruited, and 16 of them completed the study. By using a randomized double-blind crossover design, each woman was studied in two different menstrual cycles, during which placebo or OCBZ (maintenance dosage, 1,200 mg/day) was given in randomized sequence for 26 consecutive days with a washout of at least one cycle in between. A steroid oral contraceptive containing 50 microg ethinylestradiol (EE) and 250 microg levonorgestrel (LN) was taken for the first 21 days of each cycle. Plasma concentrations of EE and LN were measured by gas chromatography-mass spectrometry in samples collected at regular intervals on days 21-23 of each cycle.

RESULTS

Compared with placebo, areas under the plasma concentration curves (AUC(0-24h, geometric means) decreased by 47% for both EE (from 1,677 to 886 pg.h/ml; p < 0.01) and LN (from 137 to 73 ng.h/ml; p < 0.01), during OCBZ treatment. Peak plasma EE concentrations decreased from 180 pg/ml during the placebo cycle to 117 pg/ml during the OCBZ cycle (p < 0.01), whereas peak plasma LN concentrations decreased from 10.2 to 7.7 ng/ml (p < 0.01). The half-lives of EE and LN also decreased from 13.6 to 7.9 h (p < 0.01) and from 28.8 to 15.8 h, respectively (p < 0.01).

CONCLUSIONS

OCBZ reduces plasma concentrations of the estrogen and progestagen components of steroid oral contraceptives, presumably by stimulating their CYP3A-mediated metabolism in the liver or gastrointestinal tract or both. Because this may lead to a decreased efficacy of the contraceptive pill, women treated with OCBZ should receive preferentially a high-dosage contraceptive and should be monitored for signs of reduced hormonal cover.

Oxcarbazepine in the treatment of early childhood epilepsy

Very little data are available on the usefulness of oxcarbazepine in young children with epilepsy. From January 1991 through October 1994, we treated 53 children under age 7 years with oxcarbazepine. The mean follow-up with oxcarbazepine treatment was 13 months. Etiology was symptomatic in 39, cryptogenic in 12, and idiopathic in 2 children. Forty-three children had previously been intractable to one or more antiepileptic drugs (including carbamazepine in 30 patients) and two had carbamazepine hypersensitivity. The age at onset of oxcarbazepine therapy ranged from 0.6 to 6.9 years (mean, 3.9 yr). The mean maximum oxcarbazepine dose was 50 mg/kg/day (range, 21-86 mg/kg/day). Of the children with localization-related epilepsy, 12 of 44 (27%) became seizure free and an additional 16 of 44 (36%) had an at least 50% reduction of seizures. Five of nine children with generalized epilepsy also had some benefit but none became seizure free. In the 33 children with at least 50% seizure reduction, the mean effective dose and trough serum level of the active metabolite monohydroxycarbazepine were 47 mg/kg/day (range, 21-75 mg/kg/day) and 91 micromol/L (range, 42-130 micromol/L), respectively. Efficacy was transient in 4 children; side effects were observed in 17 children (32%); in 9 (17%) of whom, they led to dose reduction or discontinuation. Oxcarbazepine appears to be an effective and well-tolerated drug for localization-related early childhood epilepsy. Young children need a higher dose per body weight than adults.

Pharmacokinetics of new antiepileptic drugs

This article surveys the pharmacokinetic parameters for the new antiepileptic drugs (AEDs): felbamate, gabapentin, lamotrigine, oxcarbazepine, tiagabine, topiramate, and vigabatrin. Compared to the pharmacokinetics of standard AEDs, these new AEDs have progressed in terms of (a) longer half-lives, permitting once- or twice-daily dosing, (b) greatly reduced potential for drug interactions, thus increasing ease of treatment, and (c) general lack of hepatic enzyme induction, which facilitates polytherapy as well as other aspects of treatment.

Pharmacokinetic interactions of the new antiepileptic drugs

Therapy with traditional antiepileptic drugs is associated with a wide range of pharmacokinetic drug-drug interactions. In particular, enzyme induction, enzyme inhibition and displacement from protein binding may result in important changes in serum concentrations of antiepileptics. Relevant interactions have also been described for some new antiepileptics. Felbamate increases serum concentrations of phenytoin, phenobarbital and valproic acid (sodium valproate). On the other hand, it reduces concentrations of carbamazepine and increases concentrations of its metabolite carbamazepine-10,11-epoxide. Concentrations of felbamate itself are reduced by phenytoin and carbamazepine. Concentrations of lamotrigine are considerably increased by valproic acid and decreased by phenytoin, carbamazepine and phenobarbital (phenobarbitone). Vigabatrin reduces serum concentrations of phenytoin by approximately 20%. On the other hand, some new antiepileptics have the important advantage of not interfering with the metabolism of other antiepileptics; this is the case for gabapentin, lamotrigine and oxcarbazepine. Furthermore, the pharmacokinetics of gabapentin, oxcarbazepine and vigabatrin are independent of concomitant drugs. These aspects are especially important as, until now, new antiepileptics have been most often utilised as add-on therapy.

Improved detection and determination of carbamazepine and oxcarbazepine and their metabolites by high-performance liquid chromatography

An HPLC assay for carbamazepine or oxcarbazepine (OXC) and six of their metabolites in one run was applied to 35 clinical samples from patients receiving monotherapy. This rapid and economical method, utilizing a simple one-step extraction with methyl tert.-butyl ether before the run, showed recoveries of 77-108%, except for 43% for 10,11-trans-dihydroxy-10,11-dihydrocarbamazepine, from 500-microliters samples, with detection limits of 8-12 ng/ml and limits of quantification of 14-55 ng/ml depending on the compound. Indication of a new OXC metabolite, 3-hydroxycarbamazepine, was found in 2/12 patients.

Effects of felbamate on the pharmacokinetics of the monohydroxy and dihydroxy metabolites of oxcarbazepine

The effects of felbamate on the multiple dose pharmacokinetics of the monohydroxy and dihydroxy metabolites of oxcarbazepine were assessed in a placebo-controlled, randomized, double-blind crossover study in 18 healthy male volunteers. Oxcarbazepine, 1200 mg/day, was administered on an open basis in combination with double-blind placebo or 2400 mg/day felbamate for two 10-day treatment periods separated by a 14-day washout period. Pharmacokinetic parameters of monohydroxyoxcarbazepine and dihydroxyoxcarbazepine were determined from plasma and urine samples obtained on the tenth day of each treatment period. Felbamate had no effect on monohydroxyoxcarbazepine plasma or urine pharmacokinetics compared with placebo, but it significantly increased values for dihydroxyoxcarbazepine maximum concentration and area under the curve from 0 to 12 hours, as well as urinary excretion of free and total dihydroxyoxcarbazepine. The mechanism that may account for the observations is the induction of oxidative metabolism of monohydroxyoxcarbazepine. Despite these changes, the relative amount of dihydroxyoxcarbazepine is small in comparison to monohydroxyoxcarbazepine, and antiepileptic activity is associated with monohydroxyoxcarbazepine rather than dihydroxyoxcarbazepine. Therefore we conclude that felbamate has no clinically relevant effects on the pharmacokinetics of oxcarbazepine in humans.

Carbamazepine and its metabolites in human perfused placenta and in maternal and cord blood

Placental transfer and metabolism of carbamazepine (CBZ) was studied in a dual recirculating placental cotyledon perfusion system and was also evaluated in 16 pairs of maternal venous and cord blood samples. Among the parameters studied as possible indicators of a successful perfusion, volume changes in perfusate divided the perfusions into two groups, whereas no significant differences between perfusions were noted in blood gas analysis or in antipyrine transfer. CBZ added into the maternal circulation crosses the placenta in the beginning quicker than antipyrine which is in agreement with the different lipid solubilities of these compounds. Because the transfer rates of antipyrine and CBZ were about the same, the mechanism of transfer of CBZ is probably similar to that of antipyrine (passive diffusion). No metabolites of CBZ could be detected in the perfusate by high-performance liquid chromatography (HPLC) or gas chromatography/mass spectrometry. With the improved HPLC methodology for CBZ metabolites, six metabolites were detected in clinical samples, including 10-hydroxy-10,11-dihydro-CBZ (10-OH-CBZ), which has been described earlier in only 1 uremic patient. Relative levels of metabolites showed significant individual differences. CBZ crosses perfused placenta rapidly, but this does not contribute to CBZ metabolites detected in maternal and fetal circulation.

Clobazam, oxcarbazepine, tiagabine, topiramate, and other new antiepileptic drugs

Clinical investigators recently have studied at least 21 new antiepileptic drugs (AEDs) in people with epilepsy. This review briefly examines 15 of these new AEDs: clobazam (CLB), dezinamide, flunarizine (FNR), loreclezole, milacemide (MLM), MK-801, nafimidone, ORG-6370, oxcarbazepine (OCBZ), progabide (PGB), ralitoline, stiripentol, tiagabine (TGB), topiramate (TPM), and zonisamide (ZNS). CLB, PGB, and TGB represent agents that act on the GABA system, and MLM acts on the glycine system. MK-801 and ZNS (in part) are excitatory amino acid antagonists, and FNR is a calcium-channel antagonist. OCBZ is a keto analogue of carbamazepine, which is not metabolized to the epoxide and may have fewer side effects. The remaining agents are novel compounds with a variety of suspected mechanisms. TPM appears especially effective for intractable partial seizures but has a high incidence of cognitive side effects. None of these new AEDs is useful for all patients with inadequate seizure control or ongoing toxicity. The role of each will require further clinical study and experience.

Clinical pharmacokinetics of new antiepileptic drugs

We have reviewed the pharmacokinetics of six antiepileptic drugs that are marketed (felbamate, gabapentin, lamotrigine, oxcarbazepine, vigabatrin, and zonisamide) and six drugs that are undergoing evaluation (levetiracetam, ralitoline, remacemide, stiripentol, tiagabine, and topiramate). In addition, we have compared the prodrugs eterobarb and fosphenytoin and the controlled-release formulations of valproic acid and carbamazepine with their parent compounds. Finally, we have devised a scoring system to compare the pharmacokinetics of new antiepileptic drugs. Using this system, vigabatrin, levetiracetam, gabapentin, and topiramate appea to have the most favourable pharmacokinetic profiles, whilst ralitoline and stiripentol have the least favourable.

Oxcarbazepine: pharmacokinetic interactions and their clinical relevance

Antiepileptic drug (AED) interactions are a common problem during epilepsy treatment. Oxcarbazepine (OCBZ) is a keto homologue of carbamazepine (CBZ) with a completely different metabolic profile. In humans, the keto group is rapidly and quantitatively reduced to form a monohydroxy derivative (MHD), which is the main active agent during OCBZ therapy. MHD is eliminated by renal excretion, glucuronidation and, marginally, by hydroxylation to a diol derivative. This metabolic profile, and in particular the limited involvement of oxidative microsomal enzymes, suggests that OCBZ may have fewer drug interactions compared with traditional AEDs. This possibility has been investigated in experimental studies and, retrospectively, in data obtained from clinical trials. The capacity of OCBZ to induce microsomal enzymes of the P-450 family has mostly been examined by use of antipyrine and CBZ kinetics as markers. The results suggest that OCBZ has little enzyme inducing capacity. In clinical trials in which OCBZ was substituted for CBZ, plasma concentrations of concomitant AEDs were increased, possibly as a consequence of total or partial de-induction. OCBZ interference with other drugs has been evaluated for warfarin, felodipine, and oral contraceptives, three medications strongly influenced by enzyme-inducing AEDs. OCBZ does not modify the anticoagulant effect of warfarin, whereas some reduction in felodipine concentration and a clinically significant reduction of contraceptive drug levels and efficacy were observed. Polytherapy with established AEDs does not significantly modify OCBZ disposition (MHD kinetics); however, available information is not extensive. Finally, the action on OCBZ kinetics of a group of drugs (verapamil, cimetidine, erythromycin, dextropropoxyphene, and viloxazine) known to inhibit the metabolism of some AEDs has been studied.(ABSTRACT TRUNCATED AT 250 WORDS)