Beenen 1999.

Methods	Randomised double‐blind, placebo‐controlled, single‐centre (Netherlands), parallel trial 2 treatment arms: PHT and VAL Allocation concealed using sealed envelopes, trial medication identical in pre‐coded packaged materials Treatment period: 12 months Follow up: 12 months
Participants	Adults aged 21‐78 (mean age in PHT arm = 55 years, mean age in VAL arm = 51 years) Overall 47 men and 53 women, all patients undergoing craniotomy for different pathological conditions. Participants were not taking AEDs prior to randomisation and had no history of seizures. 100 randomised: 50 to PHT and 50 to VAL
Interventions	Group 1: PHT 100 mg (IV) 3 times daily administered immediately postoperation in recovery room Group 2: VAL 500 mg (IV) 3 times daily administered immediately postoperation in recovery room Participants took medication in oral form as soon as was possible for 12 months
Outcomes	Primary outcome: drug efficacy (time of and number of seizures) Secondary outcomes: tolerability (number of withdrawals, adverse effects), death, QoL and cognitive functioning
Notes	ITT analysis employed for primary outcome, not for other outcomes (QoL)
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Study used computer‐generated randomisation method
Allocation concealment (selection bias)	Low risk	Sealed envelopes, pre‐coded and packaged medication
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Adequate blinding techniques used for personnel and participants
Incomplete outcome data (attrition bias) All outcomes	Low risk	Study attrition reported, employed ITT analysis for primary outcome
Selective reporting (reporting bias)	Unclear risk	No trial protocol available
Other bias	Low risk	No other bias detected