Randomised controlled trials (RCTs) that compared allopurinol with placebo, in patients older than 18 years undergoing endoscopic retrograde cholangiopancreatography (ERCP) and/or endoscopic sphincterotomy, were eligible for inclusion. Randomised comparisons of allopurinol with placebo were eligible for inclusion regardless of the initial time of treatment, treatment duration, dose and administration route. Cointerventions were permitted if administered equally to all intervention groups. Patients with active acute pancreatitis, chronic pancreatitis, pancreatic cancer, or cancer of the papilla of Vater were excluded.
The primary outcomes were the incidence of post-ERCP pancreatitis and severe post-ERCP pancreatitis. Secondary outcomes were post-ERCP hyperamylasaemia, case-fatality ratio of post-ERCP pancreatitis, and adverse events of allopurinol. The dosage of allopurinol in included trials varied from 200 mg to 1200 mg, given orally from one hour to 24 hours before ERCP.
Two reviewers independently assessed studies for inclusion, with any disagreement resolved by discussion.