Singh 2004.

Methods	Study design: randomised controlled trial. Allocation generation: identical paper slips with either drug or placebo written, on drawn from box, patient's serial number written on slip and kept in separate box. Allocation concealment: not clearly described. Blinding: patients and observers were blinded. Loss to follow‐up: 16% ‐ it is not specified to which group these participants were allocated to.
Participants	Total number of participants randomised:100. Inclusion criteria: primigravidae at term with singleton pregnancy, vertex presentation, established spontaneous labour, cervical dilatation of at least 3 cm. Exclusion criteria: any medical, surgical or obstetric complications.
Interventions	Intervention: Drotaverine hydrochloride 40 mg (2 mL) IMI in active labour, cervix at least 3 cm dilated. n = 50. Control: Distilled water 2 mL IMI in active labour, cervix at least 3 cm dilated.. n = 50.
Outcomes	Primary outcomes: 1. Duration of first stage of labour (time of intervention to full cervical dilatation). 2. Pain. 3. Cervical dilatation rate. Secondary outcomes: 1. Maternal and neonatal outcome. 2. Side effects.
Notes	Ethics: approved by institutional ethical committee, informed consent obtained. Location: Delhi, India. Authors contacted:
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Identical paper slips 50 with "drug" and 50 with "placebo" written on. A slip was drawn from the box and patient's serial no written on it, kept in separate box.
Allocation concealment (selection bias)	High risk	No allocation concealment took place. The nurse administering the intervention knew whether placebo or active ingredient was administered. The paper slips were not sequentially numbered, but explicitly stated "drug" or "placebo".
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Participant was blinded, nurse administering intervention was not blinded.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Outcome assessor was blinded.
Incomplete outcome data (attrition bias) All outcomes	High risk	100 patients were enrolled, 16 were excluded before intervention was administered. 4 patients had caesarean section due to fetal distress, 5 patients opted out of the study and 7 had incomplete data. It is not mentioned to which group all these participants belonged to, which is inadequate.
Selective reporting (reporting bias)	Unclear risk	Duration of different stages of labour: adequately reported cervical dilatation rate: only reported in bar‐chart. The mean cervical dilatation rate of the intervention group is mentioned, but not of the control group. Pain assessment results are adequately reported It is not stated how many instrumental deliveries or caesarean section were done after the intervention.
Other bias	High risk	The starting point of the intervention was not the same in every participant. It varied from 3‐6 cm cervical dilatation. The number of participants in each group was not the same. In the group that received the intervention at 6 cm, there were 18 in the treatment group compared to 3 in the control group. The results presented are not statistically significant, but imbalances like that introduce bias. Drug company sponsorship: not mentioned.