Oxcarbazepine add-on for drug-resistant focal epilepsy

BACKGROUND: Epilepsy is a common neurological disorder. In approximately 30% of epilepsy cases, seizures are uncontrolled by one antiepileptic drug (AED). These people require treatment with a combination of multiple AEDs and are described as having drug‐resistant epilepsy. Oxcarbazepine is a keto‐analogue of carbamazepine, an established AED, and can be used as an add‐on treatment for drug‐resistant epilepsy. OBJECTIVES: To assess the efficacy and tolerability of oxcarbazepine as an add‐on treatment for people with drug‐resistant focal epilepsy. SEARCH METHODS: The following databases were searched on 24 September 2018: Cochrane Register of Studies (CRS Web), which includes the Cochrane Epilepsy Group Specialized Register and the Cochrane Central Register of Controlled Trials (CENTRAL); Medline (Ovid) 1946 to 21 September 2018; ClinicalTrials.gov; and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP). Originally, we also searched SCOPUS as a substitute for Embase, but this is no longer necessary, because randomised and quasi‐randomised controlled trials in Embase are now included in CENTRAL. SELECTION CRITERIA: Randomised controlled trials with parallel‐group or cross‐over design, recruiting people of any age with drug‐resistant focal epilepsy. We accepted any level of blinding and trials could be placebo‐ or active‐controlled. DATA COLLECTION AND ANALYSIS: In accordance with the methodological procedures expected by the Cochrane Collaboration, two review authors independently assessed trial eligibility before extracting data and assessing risk of bias. We assessed the primary outcomes: median percentage seizure reduction per 28 days; 50% or greater reduction in seizure frequency; and adverse effects including ataxia, hyponatraemia, and somnolence. We assessed the secondary outcomes: seizure freedom; treatment withdrawal; cognitive effects; and quality of life. We used an intention‐to‐treat population for all primary analyses. We present results as risk ratios (RR) with 95% confidence intervals (CI), with the exception of adverse effects which we present with 99% CI. MAIN RESULTS: We identified six eligible studies, involving 1593 participants. We judged that three studies were at unclear risk of bias and three were at high risk of bias. Bias mainly arose from lack of methodological details and from high attrition rates. Participants were aged 1 month to 65 years, with a diagnosis of drug‐resistant focal epilepsy. All studies were either placebo‐ or alternative‐dose‐controlled with parallel‐group design. The treatment period varied from 9 days to 26 weeks. The median percentage seizure reduction per 28 days (3 studies; moderate‐certainty evidence) ranged from 26% to 83.3% for participants randomised to experimental oxcarbazepine compared to 7.6% to 28.7% for participants randomised to control treatment. Oxcarbazepine may increase the responder rate for 50% or greater reduction in seizure frequency compared to control treatment (RR 1.80, 95% CI 1.27 to 2.56; random‐effects model; 6 studies; low‐certainty evidence). For seizure freedom, the RR was 2.86 (95% CI 1.19 to 6.87; random‐effects model; 5 studies; low‐certainty evidence), suggesting an advantageous effectiveness of oxcarbazepine over control treatment. Treatment with oxcarbazepine was associated with an increased treatment withdrawal rate compared to control (RR 1.75, 95% CI 1.44 to 2.13; fixed‐effect model; 6 studies; moderate‐certainty evidence). The largest oxcarbazepine dose used, 2400 mg/d, was associated with a higher treatment withdrawal rate (RR 2.38, 95% CI 1.92 to 2.94; fixed‐effect model; 2 studies) compared to control, than 1200 mg/d (RR 1.54, 95% CI 1.21 to 1.95; fixed‐effect model; 3 studies) or 600 mg/d oxcarbazepine (RR 0.79, 95% CI 0.55 to 1.15; fixed‐effect model; 1 study). Treatment with oxcarbazepine was associated with an increased incidence of multiple adverse effects including: ataxia (RR 2.54, 99% CI 0.86 to 7.54; random‐effects model; 5 studies; moderate‐certainty evidence); and somnolence (RR 2.03, 99% CI 1.17 to 3.54; random‐effects model; 6 studies; low‐certainty evidence). Hyponatraemia occurred more frequently with oxcarbazepine treatment but not significantly so (RR 2.53, 99% CI 0.27 to 23.85; fixed‐effect model; 6 studies; moderate‐certainty evidence). AUTHORS' CONCLUSIONS: Oxcarbazepine might be effective at reducing seizure frequency when used as an add‐on for drug‐resistant focal epilepsy. The efficacy outcomes — 50% or greater seizure reduction and seizure freedom — were derived from low‐certainty evidence. We are, therefore, uncertain whether the estimated effect size is representative of the true effect. In contrast, the evidence for median percentage seizure reduction and treatment withdrawal were of moderate certainty: thus, we are fairly certain of the effect estimates' reliability. Overall, we are unsure of the true efficacy of oxcarbazepine, but have concerns about its tolerability.