Background: This is an update of the Cochrane Review first published in 2010; it includes one additional study. Primary generalised tonic-clonic seizures are a type of generalised seizure. Other types of seizures include: absence, myoclonic, and atonic seizures. Effective control of tonic-clonic seizures reduces the risk of injury and death, and improves quality of life. While most people achieve seizure control with one antiepileptic drug, around 30% do not, and require a combination of antiepileptic drugs.

Objectives: To assess the effectiveness and tolerability of add-on lamotrigine for drug-resistant primary generalised tonic-clonic seizures.

Search methods: For the latest update, we searched these databases on 19 March 2019: Cochrane Register of Studies (CRS) Web, MEDLINE Ovid, and the WHO International Clinical Trials Registry Platform (ICTRP). The CRS includes records from the Cochrane Epilepsy Group Specialized Register, CENTRAL, Embase, and ClinicalTrials.gov. We imposed no language restrictions. We also contacted GlaxoSmithKline, manufacturers of lamotrigine.

Selection criteria: Randomised controlled parallel or cross-over trials of add-on lamotrigine for people of any age with drug-resistant primary generalised tonic-clonic seizures.

Data collection and analysis: We followed standard Cochrane methodology; two review authors independently assessed trials for inclusion, evaluated risk of bias, extracted relevant data, and GRADE-assessed evidence. We investigated these outcomes: (1) 50% or greater reduction in primary generalised tonic-clonic seizure frequency; (2) seizure freedom; (3) treatment withdrawal; (4) adverse effects; (5) cognitive effects; and (6) quality of life. We used an intention-to-treat (ITT) population for all analyses, and presented results as risk ratios (RRs) with 95% confidence intervals (CIs); for adverse effects, we used 99% CIs to compensate for multiple hypothesis testing.

Main results: We included three studies (total 300 participants): two parallel-group studies and one cross-over study. We assessed varied risks of bias across studies; most limitations arose from the poor reporting of methodological details. We meta-analysed data extracted from the two parallel-group studies, and conducted a narrative synthesis for data from the cross-over study. Both parallel-group studies (270 participants) reported all dichotomous outcomes. Participants taking lamotrigine were almost twice as likely to attain a 50% or greater reduction in primary generalised tonic-clonic seizure frequency than those taking a placebo (RR 1.88, 95% CI 1.43 to 2.45; low-certainty evidence). The results between groups were inconclusive for the likelihood of seizure freedom (RR 1.55, 95% CI 0.89 to 2.72; very low-certainty evidence); treatment withdrawal (RR 1.20, 95% CI 0.72 to 1.99; very low-certainty evidence); and individual adverse effects: ataxia (RR 3.05, 99% CI 0.05 to 199.36); dizziness (RR 0.91, 99% CI 0.29 to 2.86; very low-certainty evidence); fatigue (RR 1.02, 99% CI 0.13 to 8.14; very low-certainty evidence); nausea (RR 1.60, 99% CI 0.48 to 5.32; very low-certainty evidence); and somnolence (RR 3.73, 99% CI 0.36 to 38.90; low-certainty evidence). The cross-over trial (26 participants) reported that 7/14 participants with generalised tonic-clonic seizures experienced a 50% or greater reduction in seizure frequency with add-on lamotrigine compared to placebo. The authors reported four treatment withdrawals, but did not specify during which treatment allocation they occurred. Rash (seven lamotrigine participants; zero placebo participants) and fatigue (five lamotrigine participants; zero placebo participants) were the most frequently reported adverse effects. None of the included studies measured cognition. One parallel-group study (N = 153) evaluated quality of life. They reported inconclusive results for the overall quality of life score between groups (P = 0.74).

Authors' conclusions: This review provides insufficient information to inform clinical practice. Low-certainty evidence suggests that lamotrigine reduces the rate of generalised tonic-clonic seizures by 50% or more. Very low-certainty evidence found inconclusive results between groups for all other outcomes. Therefore, we are uncertain to very uncertain that the results reported are accurate, and suggest that the true effect could be grossly different. More trials, recruiting larger populations, over longer periods, are necessary to determine lamotrigine's clinical use.