Methods	RCT 2-arm parallel group design.
Participants	Setting: UK hospital. 1,100 women. 37-42 weeks’ gestation, in active labour and requiring analgesia Parity: 44% primips, 56% multips.
Interventions	Experimental: IM meptazinol 100 mg ≤ 70 kg, 150 mg > 70 kg (N = 513) Control: IM pethidine 1100 mg ≤ 70 kg, 150 mg > 70 kg (N = 522) Second dose, epidural or inhalation analgesia at maternal request
Outcomes	Maternal outcomes: maternal pain at 30, 60, 90 and 120 minutes VAS (0-100 mm), nausea, vomiting, sleepiness, use of supplementary analgesia, method of birth, opinion of analgesic effect assessed 3-5 days postpartum (rated excellent, good, poor but just able to cope, no effect and required additional analgesia). Neonatal outcomes: Apgar at 1 and 5 min, resuscitation, naloxone administration, fetal distress, type of feeding
Notes
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not reported.
Allocation concealment (selection bias)	Low risk	Coded drug containers prepared at a site remote from the trial
Blinding (performance bias and detection bias) Women	Low risk	States double blind and used coded drug containers.
Blinding (performance bias and detection bias) Clinical staff	Low risk	States double blind and used coded drug containers.
Blinding (performance bias and detection bias) Outcome assessor	Low risk	States double blind and used coded drug containers.
Incomplete outcome data (attrition bias) All outcomes	High risk	65 women excluded due to clerical errors or administration of wrong drug
Selective reporting (reporting bias)	Unclear risk	Unclear.
Other bias	Unclear risk	Women were balanced at baseline for age, weight, parity and gestation