Oxcarbazepine versus phenytoin monotherapy for epilepsy.

BACKGROUND: Worldwide, phenytoin is a commonly used antiepileptic drug. Oxcarbazepine is one of the newer antiepileptic drugs and has similar chemical properties to its parent compound carbamazepine. For the new drugs such as oxcarbazepine, it is important to know how they compare with standard treatments.

OBJECTIVES: To review the best evidence comparing oxcarbazepine and phenytoin when used as monotherapy in patients with epilepsy.

SEARCH STRATEGY: We searched the Cochrane Epilepsy Group's Specialized Register (December 2005), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 3, 2005), and MEDLINE (1966 to November 2005). No language restrictions were imposed. We checked the reference lists of retrieved studies for additional reports of relevant studies. We also contacted pharmaceutical companies to try and identify any unpublished studies.

SELECTION CRITERIA: Randomized controlled trials in children or adults with epilepsy. Trials must have included a comparison of oxcarbazepine monotherapy with phenytoin monotherapy.

DATA COLLECTION AND ANALYSIS: This was an individual patient data review. Two review authors independently assessed trial quality and extracted data. Study authors were contacted for additional information. Outcomes were (a) time on allocated treatment; (b) time to achieve 6, 12 and 24-month remission; (c) time to first seizure post randomization; (d) quality of life measures if available. Clinical heterogeneity was assessed by reviewing differences across trials in characteristics of randomized patients, dosing protocols and trial design. Data were analysed on an intention to treat basis. Stratified logrank tests were used to obtain study-specific and overall estimates of hazard ratios (with 95% confidence intervals), where a HR > 1 indicates that an event is more likely on phenytoin.

MAIN RESULTS: Individual patient data were available for 480 patients from two trials, representing 100% of the patients recruited into the two trials that met our inclusion criteria. By convention, for the outcomes time to withdrawal of allocated treatment and time to first seizure a hazards ratio (HR) > 1 indicates a clinical advantage for oxcarbazepine and for time to 6 and 12-month remission a HR > 1 indicates a clinical advantage for phenytoin. The main overall results (HR, 95% confidence interval (CI)) were: (i) time to withdrawal of allocated treatment 1.64 (1.09 to 2.47), (ii) time to 6-month remission 0.89 (0.66 to 1.22), (iii) time to 12-month remission 0.92 (0.62 to 1.37), (iv) time to first seizure 1.07 (0.83 to 1.39). The overall results indicate that oxcarbazepine is significantly better than phenytoin for time to treatment withdrawal, but suggest no overall difference between oxcarbazepine and phenytoin for other outcomes. Results stratified by seizure type indicate no significant advantage for either drug for patients with generalized onset seizures, but a potentially important advantage in time to withdrawal for oxcarbazepine for patients with partial onset seizures: HR 1.92 (95% CI 1.17 to 3.16). The age distribution of adults classified as having generalized epilepsy suggests a significant number of patients may have had their epilepsy misclassified.

AUTHORS' CONCLUSIONS: For patients with partial onset seizures oxcarbazepine is significantly less likely to be withdrawn, but current data do not allow a statement as to whether oxcarbazepine is equivalent, superior or inferior to phenytoin in terms of seizure control. Guidelines recommend carbamazepine as a first line treatment for patients with partial onset seizures and more evidence is needed regarding the comparative effects of oxcarbazepine and carbamazepine to further inform policy. For patients with generalized onset tonic-clonic seizures, valproate is considered the first line standard treatment and the results of this review do not inform current treatment policy. Misclassification of patients' epilepsy type may have confounded the results of this review.