North 1983.

Study characteristics
Methods	Randomised, double‐blinded, placebo‐controlled, parallel, single‐centre trial, Australia 2 treatment arms: PHT and placebo Participants received identical medication (no details available of randomisation methods) Treatment period: 12 months Follow up: 12 months
Participants	Adults, mean age 46.7 years (PHT) and 50.21 years (placebo), all undergoing supratentorial craniotomy. Participants had no previous exposure to AEDs and no previous history of epilepsy. 281 patients were randomised: 140 to PHT and 141 to placebo
Interventions	Group 1: PHT 250 mg twice daily administered (IV) first dose administered in the recovery room postcraniotomy followed by oral medication 100 mg 3 times daily for 12 months Group 2: placebo medication administered as described above.
Outcomes	Primary outcome: efficacy (number of seizures) Secondary outcomes: survival time (number of days since randomisation to incidence of seizure or to 365 days in seizure‐free participants), adverse effects
Notes	63 participants in PHT arm and 59 participants in placebo arm received intended treatment. All cases randomised were analysed
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 used for both groups. Only pharmacologist aware of serum drug levels and both PHT and placebo group participants had blood samples taken.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Attrition reported and ITT analysis employed. 6 participants lost to follow‐up
Selective reporting (reporting bias)	Unclear risk	Protocol outlined within paper. All outcomes reported. Full protocol not available
Other bias	Low risk	No other bias detected