Nakamura 1999.

Methods	Randomised, double‐blind, controlled, multi‐centre (Japan) trial 2 treatment arms: ZNS and PB. Identical medication administered (no details of methods of randomisation). Treatment period: 1 year. Follow‐up period: 3 years
Participants	278 patients who were scheduled to receive craniotomy for cerebral tumours, cerebrovascular diseases and head trauma, were randomised. 129 in ZNS group analysed, 126 in PB group were analysed
Interventions	Group 1: ZNS (100 mg twice daily) until 1 month after craniotomy Group 2: PB (40 mg twice daily) until 1 month after craniotomy In both groups dose was adjusted to therapeutic serum concentration and continued up to 1 year
Outcomes	Primary outcome: frequency of epilepsy Secondary outcome: drug concentration, adverse effects.
Notes	23 'unsuitable cases' not included in the analysis. 36 cases not followed up for full 3 years of the study
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	No details in text
Allocation concealment (selection bias)	Unclear risk	No details in text
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Identical medication administered to both groups. Drug name blinded from participating institutions, only blood concentration values provided
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	23 cases not included within analysis, all excluded prior to treatment. 36 lost to follow‐up were included in analysis
Selective reporting (reporting bias)	Unclear risk	Trial reports data for overall adverse effects, only reports data for 2 individual adverse effects
Other bias	Low risk	No other bias detected