Patel 1980

Methods	Randomised, double blind, active (pethidine) control, single IM dose. Study duration 6 h. Baseline PI = severe Self assessment at t = 0.30, 1, then hourly up to 6 h.
Participants	Elective exploratory laparotomy N = 100 M 82, F 18 Mean age 40 years
Interventions	Dipyrone 2.5 g IM, n = 51 Pethidine 100 mg IM, n = 49
Outcomes	PR: standard 5 point scale (0‐4) Adverse events
Notes	Oxford Quality Score: R1, DB1, W0. Total = 2 Rescue medication allowed after 1 h
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not reported
Allocation concealment (selection bias)	Unclear risk	Not reported
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Study medication not indistinguishable, but administered by research worker who had no contact with other investigators