Faiz 2014.

Methods	Randomized, double‐blind, active‐controlled. Evaluated up to 24 h after surgery. Medications administered prior to skin closure
Participants	Type of surgery: elective abdominal hysterectomy Paracetamol group Entered/completing: 40/40 Age (mean, SD): 49.9 ± 6.9 Sex (male, %): 0 Control group Entered/completing: 40/40 Age (mean, SD): 47.2 ± 7.2 Sex (male, %): 0
Interventions	Paracetamol 15 mg/kg in 100 ml NS, single dose over 15 min Ketamine 0.15 mg/kg administered as above
Outcomes	Primary: pain (VAS 0 to 10) in recovery room and at 4, 6, 12 and 24 h postop Secondary: sedation (Ramsay scale), adverse events (nausea, vomiting, respiratory complications, hemodynamic changes), rescue analgesia (pethidine 15 mg for VAS pain > 3)
Source of funding	Iran University of Medical Sciences
Were treatment groups comparable at baseline?	Yes: demographics and duration of surgery
Details of preoperative pain	Not reported, but participants currently using opioids were excluded
Notes	Low dose of ketamine used in comparator group
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Block randomization
Allocation concealment (selection bias)	Unclear risk	Not mentioned
Blinding (performance bias and detection bias) All outcomes	Low risk	“Both medication solutions were prepared by the research pharmacist in 100 ml of normal saline and were administered by the anesthesia care team within a 15‐minute time period. The administering team was blinded to the nature of the infusate”.
Incomplete outcome data (attrition bias) All outcomes	Low risk	No dropouts; tables suggest that all participants reported data
Selective reporting (reporting bias)	Low risk	All planned primary and secondary outcomes reported, although total amount of rescue analgesia not reported. Confirmed on trials registry (http://www.irct.ir/searchresult.php?id=11319&number=1).
Size	High risk	Fewer than 50 participants per arm of the study (40 paracetamol, 40 ketamine)