Pregabalin add-on for drug-resistant partial epilepsy

Epilepsy is a common chronic neurological disease with an estimated prevalence of 1% in the UK. Approximately one third of these people continue to have seizures despite drug treatment. In order to try to improve outcomes a number of new antiepileptic drugs have been developed and pregabalin is one of these. This review is an update of a previous Cochrane review (Pulman 2008); no further studies have been added since the previous update in 2012 and only one study has been identified as an ongoing trial.

To summarise evidence from randomised controlled trials regarding the efficacy and tolerability of pregabalin when used as an add-on antiepileptic treatment in drug-resistant partial epilepsy. The definitions of drug resistance used were those employed by the authors of the included trials.

We searched the Cochrane Epilepsy Group Specialized Register (Jan 2014), CENTRAL (the Cochrane Central Register of Controlled Trials, The Cochrane Library 2013, Issue 12), MEDLINE (Ovid, 1946 to 09/01/2014) and contacted Pfizer Ltd. (the manufacturers of pregabalin) to identify published, unpublished and ongoing trials.

We included randomised controlled trials comparing pregabalin with placebo or an alternative antiepileptic drug for people with drug-resistant partial epilepsy. Outcomes included 50% or greater reduction in seizure frequency, seizure freedom, treatment withdrawal for any reason, treatment withdrawal for adverse events and nature of adverse events.

Two review authors (JP and AGM) independently selected and assessed suitable trials and extracted data. Primary analyses were by intention-to-treat (ITT). Results are presented as risk ratios (RR) with 95% confidence intervals (CI). Included studies were assessed for risk of bias by two authors using the Cochrane 'Risk of bias' tool.

Six suitable industry-sponsored trials (2009 participants) were identified and included in the analysis. Trials tested doses of pregabalin ranging from 50 mg/day to 600 mg/day. For the primary outcome, 50% or higher seizure reduction was significantly more likely in patients randomised to pregabalin than to placebo (RR 2.61; 95% CI 1.70 to 4.01). A dose-response analysis suggested increasing effect with increasing dose. Pregabalin was significantly associated with seizure freedom (RR 2.59; 95% CI 1.05 to 6.36). Patients were significantly more likely to have withdrawn from pregabalin treatment than placebo treatment for any reason (RR 1.39; 95% CI 1.13 to 1.72) or for adverse effects (RR 2.69; 95% CI 1.88 to 3.86). Ataxia, dizziness, somnolence and weight gain were significantly associated with pregabalin. The odds of response doubled with an increase in dose from 300 mg/day to 600 mg/day (OR 2.12; 95% CI 1.76 to 2.54). Overall, the evidence was rated as low/unclear risk of bias due to the possibility of publication bias. The quality of the evidence was rated as moderate using the GRADE approach.

Pregabalin, when used as an add-on drug for treatment-resistant partial epilepsy, is significantly more effective than placebo at achieving a 50% or greater seizure reduction and significantly increasing seizure freedom. Results demonstrate efficacy for doses from 150 mg/day to 600 mg/day, with increasing effectiveness at 600 mg doses. The trials included in this review were of short duration and longer-term trials are needed to inform clinical decision making better.