Carbamazepine versus phenytoin monotherapy for epilepsy: an individual participant data review.

BACKGROUND

This is an update of a Cochrane Review first published in 2002 and last updated in 2017. This review is one in a series of Cochrane Reviews investigating pair-wise monotherapy comparisons.Epilepsy is a common neurological condition in which abnormal electrical discharges from the brain cause recurrent unprovoked seizures. It is believed that with effective drug treatment, up to 70% of individuals with active epilepsy have the potential to become seizure-free and go into long-term remission shortly after starting drug therapy with a single antiepileptic drug in monotherapy.Worldwide, carbamazepine and phenytoin are commonly-used broad spectrum antiepileptic drugs, suitable for most epileptic seizure types. Carbamazepine is a current first-line treatment for focal onset seizures in the USA and Europe. Phenytoin is no longer considered a first-line treatment, due to concerns over adverse events associated with its use, but the drug is still commonly used in low- to middle-income countries because of its low cost. No consistent differences in efficacy have been found between carbamazepine and phenytoin in individual trials; however, the confidence intervals generated by these trials are wide, and therefore, synthesising the data of the individual trials may show differences in efficacy.

OBJECTIVES

To review the time to treatment failure, remission and first seizure with carbamazepine compared with phenytoin when used as monotherapy in people with focal onset seizures (simple or complex focal and secondarily generalised), or generalised onset tonic-clonic seizures (with or without other generalised seizure types).

SEARCH METHODS

For the latest update, we searched the following databases on 13 August 2018: the Cochrane Register of Studies (CRS Web), which includes the Cochrane Epilepsy's Specialised Register and CENTRAL; MEDLINE; the US National Institutes of Health Ongoing Trials Register (ClinicalTrials.gov); and the World Health Organization International Clinical Trials Registry Platform (ICTRP). We handsearched relevant journals and contacted pharmaceutical companies, original trial investigators, and experts in the field.

SELECTION CRITERIA

Randomised controlled trials comparing monotherapy with either carbamazepine or phenytoin in children or adults with focal onset seizures or generalised onset (tonic-clonic) seizures.

DATA COLLECTION AND ANALYSIS

This was an individual participant data (IPD) review. Our primary outcome was time to treatment failure. Our secondary outcomes were time to first seizure post-randomisation, time to six-month remission, time to 12-month remission, and incidence of adverse events. We used Cox proportional hazards regression models to obtain trial-specific estimates of hazard ratios (HRs), with 95% confidence intervals (CIs), using the generic inverse variance method to obtain the overall pooled HR and 95% CI.

MAIN RESULTS

IPD were available for 595 participants out of 1102 eligible individuals, from four out of 11 trials (i.e. 54% of the potential data). For remission outcomes, a HR greater than 1 indicates an advantage for phenytoin; and for first seizure and withdrawal outcomes, a HR greater than 1 indicates an advantage for carbamazepine. Most participants included in analysis (78%) were classified as experiencing focal onset seizures at baseline and only 22% were classified as experiencing generalised onset seizures; the results of this review are therefore mainly applicable to individuals with focal onset seizures.Results for the primary outcome of the review were: time to treatment failure for any reason related to treatment (pooled HR adjusted for seizure type for 546 participants: 0.94, 95% CI 0.70 to 1.26, moderate-certainty evidence); time to treatment failure due to lack of efficacy (pooled HR adjusted for seizure type for 546 participants: 0.99, 95% CI 0.69 to 1.41, moderate-certainty evidence); both showing no clear difference between the drugs and time to treatment failure due to adverse events (pooled HR adjusted for seizure type for 546 participants: 1.27, 95% CI 0.87 to 1.86, moderate-certainty evidence), showing that treatment failure due to adverse events may occur earlier on carbamazepine than phenytoin, but we cannot rule out a slight advantage to carbamazepine or no difference between the drugs.For our secondary outcomes (pooled HRs adjusted for seizure type), we did not find any clear differences between carbamazepine and phenytoin: time to first seizure post-randomisation (582 participants): 1.15, 95% CI 0.94 to 1.40, moderate-certainty evidence); time to 12-month remission (551 participants): 1.00, 95% CI 0.79 to 1.26, moderate-certainty evidence); and time to six-month remission (551 participants): 0.90, 95% CI 0.73 to 1.12, moderate-certainty evidence).For all outcomes, results for individuals with focal onset seizures were similar to overall results (moderate-certainty evidence), and results for the small subgroup of individuals with generalised onset seizures were imprecise, so we cannot rule out an advantage to either drug, or no difference between drugs (low-certainty evidence). There was also evidence that misclassification of seizure type may have confounded the results of this review, particularly for the outcome 'time to treatment failure'. Heterogeneity was present in analysis of 'time to first seizure' for individuals with generalised onset seizures, which could not be explained by subgroup analysis or sensitivity analyses.Limited information was available about adverse events in the trials and we could not compare the rates of adverse events between carbamazepine and phenytoin. Some adverse events reported on both drugs were abdominal pain, nausea, and vomiting, drowsiness, motor and cognitive disturbances, dysmorphic side effects (such as rash).

AUTHORS' CONCLUSIONS: Moderate-certainty evidence provided by this systematic review does not show any differences between carbamazepine and phenytoin in terms of effectiveness (retention) or efficacy (seizure recurrence and seizure remission) for individuals with focal onset or generalised onset seizures.However, some of the trials contributing to the analyses had methodological inadequacies and inconsistencies, which may have had an impact on the results of this review. We therefore do not suggest that results of this review alone should form the basis of a treatment choice for a person with newly-onset seizures. We did not find any evidence to support or refute current treatment policies. We implore that future trials be designed to the highest quality possible, with consideration of masking, choice of population, classification of seizure type, duration of follow-up, choice of outcomes and analysis, and presentation of results.