Oxcarbazepine in the treatment of epilepsy

Causes and management of hyponatremia

OBJECTIVE

To review clinical information on the incidence and causes of hyponatremia (defined as a serum sodium level <130 mEq/L), the most common electrolyte abnormality seen in general hospital patients, and to discuss the diagnosis and treatment of hyponatremia in relation to these factors.

DATA SOURCES

Primary sources and review articles were identified via MEDLINE (1981-July 2003) for entries on hyponatremia. We limited the search to specific topics including incidence, risk factors, diagnosis, treatment, and clinical disorders and medications associated with hypotonic hyponatremia.

STUDY SELECTION AND DATA EXTRACTION

All of the articles identified were evaluated, and relevant and representative information was included in this review.

DATA SYNTHESIS

Hyponatremia can result from several disease states, injury, surgery, physical exercise, or the administration of certain drugs (e.g., antidepressants, antiepileptics) and is associated with advanced age. Drug-induced hyponatremia is often asymptomatic and usually resolves following water restriction and monitoring of medication. Symptoms of hyponatremia are primarily neurologic; the principal danger of hyponatremia relates to effects on central nervous system function due to changes in brain size.

CONCLUSIONS

Although hyponatremia can be a serious condition, appropriate measures for the management of at-risk and affected patients will lead to full recovery in most cases.

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.

Clinical trials for treatment of primary generalized epilepsies

PURPOSE

To review the current state of knowledge of the treatment of primary (idiopathic) generalized epilepsy syndromes based on the efficacy results of clinical trials, to highlight obstacles in the design of these trials, and to suggest solutions for future research.

METHODS

Published reports of controlled clinical trials, as well as large or significant uncontrolled trials of treatments for these syndromes, were reviewed. Trials were selected for discussion based on their importance or their illustration of design issues.

RESULTS

Only a few randomized, controlled trials of therapy for these syndromes exist. Conclusions based on this Class I data include efficacy in absence epilepsies for ethosuximide, valproate, and lamotrigine, and for eight drugs for primary generalized tonic-clonic seizures. Many commonly accepted therapeutic strategies are not based on formal data. No controlled data exist for uncommon syndromes.

CONCLUSIONS

More clinical trials of therapies for primary generalized epilepsies are needed. To overcome design obstacles, better funding, multicenter cooperation, inclusion of children, study designs requiring fewer patients, equivalent-control designs, use of EEG and video seizure counting, and better syndrome identification will be required.

Therapeutics in pediatric epilepsy, Part 1: The new antiepileptic drugs and the ketogenic diet

Epilepsy is one of the most common and challenging neurologic disorders affecting children. Although various modalities exist to treat pediatric-onset seizures, seizures in 25% of children who are diagnosed as having epilepsy remain refractory to available therapies. Of the 8 new antiepileptic drugs (AEDs) (felbamate, gabapentin, lamotrigine, topiramate, tiagabine, levetiracetam, oxcarbazepine, and zonisamide), all but 2 (zonisamide and levetiracetam) have received Food and Drug Administration approval for adjunctive use in the pediatric population. However, most of the new AEDs used in adults have also been used in children, beyond the AEDs' approved indications. The ultimate goal of patient management is to choose the therapeutic option that provides the best chance of improving the patient's quality of life. Issues that relate to treatment choice include the likelihood of seizure recurrence, type and severity of seizures, available AED efficacies and toxicities, need for hematologic monitoring, ease of dosing, underlying medical conditions, medication interactions, urgency of initiating therapy, and cost. In this review, we discuss these issues for each of the 8 new AEDs; we also discuss the ketogenic diet and briefly review the older AEDs. Knowledge of the available AEDs will enable the practitioner to choose the best drug or drugs for individual 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.