Glantz 1996.

Methods	Random allocation, double‐blind, placebo‐controlled design with calculation of sample size
Participants	Metastatic or primary brain tumors without history of seizures Placebo group: Lung cancer (n=28), non‐Hodgkin lymphoma (n=2), glioblastoma (n=4), melanoma (n=1), other (n=2). Treatment group: lung cancer (n=23), breast cancer (n=4), GBM (n=5), melanoma (n=1), and other tumors (n=4)
Interventions	Patients took placebo or valproic acid. Dose of valproic acid was adjusted to levels 50‐100 ug/mL
Outcomes	There was no difference between valproic acid and placebo to prevent seizures (P=0.7, Fisher test)
Notes	This trial had the highest methodological validity. It also avoided the confounding effect of surgery on seizures since participants entered the trial after 14 days of diagnosis
Risk of bias
Bias	Authors' judgement	Support for judgement
Allocation concealment?	Low risk	A ‐ Adequate