McKenzie 1997.

Study characteristics
Methods	Study design: randomized controlled trial Study grouping: 2 groups, monoprophylaxis and combination prophylaxis
Participants	Baseline characteristics Ondansetron Assessed for eligibility (n): ‐ Enrolled (n): ‐ Randomized (n): 40 Received treatment (n): 40 Analysed (n): 40 Age (mean ± SD, median (IQR), median (range), mean (CI low, high)): 40 (37.0 to 42.3) Weight (mean ± SD, median (IQR), median (range)): 67 (62.7 to 71.5) BMI (mean ± SD, median (IQR), median (range)): NA ASA I/II/III/IV (n): NA/NA/NA/0 Gender (female in %): 100 Non‐smoker (%): NA History of PONV/motion sickness (%): 50/25 Type of general anaesthesia: inhalational anaesthesia (N₂O + isoflurane) Duration of anaesthesia or surgery (in min; as mean or median): 107 Use of perioperative opioids (if yes, which?): 393 µg fentanyl, 47 mg morphine via PCA in 24 hours Type of surgery: major gynaecological surgery Ondansetron + dexamethasone Assessed for eligibility (n): ‐ Enrolled (n): ‐ Randomized (n): 40 Received treatment (n): 40 Analysed (n): 40 Age (mean ± SD, median (IQR), median (range), mean (CI low, high)): 41 (38.5 to 43.8) Weight (mean ± SD, median (IQR), median (range)): 70 (66.5 to 73.9) BMI (mean ± SD, median (IQR), median (range)): NA ASA I/II/III/IV (n): NA/NA/NA/0 Gender (female in %): 100 Non‐smoker (%): NA History of PONV/motion sickness (%): 50/36 Type of general anaesthesia: inhalational anaesthesia (N₂O + isoflurane) Duration of anaesthesia or surgery (in min; as mean or median): 100 Use of perioperative opioids (if yes, which?): 436 µg fentanyl, 50 mg morphine via PCA in 24 hours Type of surgery: major gynaecological surgery Included criteria: after approval of the Magee‐Women's Hospital Institutional Review Board, informed consent was obtained from 80 women 18 to 65 years of age, who were scheduled for major gynaecological surgery. All women were ASA I, II, or III Excluded criteria: diabetes; had recently (within 24 hours) ingested any other medicine with potential antiemetic properties; had hypersensitivity to soybean, ondansetron, or corticoids; if continuous gastric suction was ordered during the 24‐hour postoperative period Pretreatment: baseline characteristics (age, weight): no; (ASA): unclear. Potential effect modifiers (gender, duration of anaesthesia, history of PONV/motion sickness, perioperative opioids): no; (non‐smoker): unclear
Interventions	Intervention characteristics Ondansetron Dose: 4 mg Time point of administration: ondansetron with saline after induction of anaesthesia Route of administration: IV Rescue antiemetics (if yes, which?): 57.5% (droperidol 0.625 mg IV, prochlorperazine IM) Ondansetron + dexamethasone Dose: ondansetron 4 mg, dexamethasone 20 mg Time point of administration: after induction of anaesthesia Route of administration: IV Rescue antiemetics (if yes, which?): 47,5% (droperidol 0.625 mg IV, prochlorperazine IM)
Outcomes	Vomiting (0 to 24 hours) Outcome type: dichotomous outcome Vomiting (0 to 2 hours) Outcome type: dichotomous outcome Nausea (0 to 24 hours) Outcome type: dichotomous outcome Complete response (no PONV) in 24 hours Outcome type: dichotomous outcome Adverse events (general notes in the publication, 24 hours' observation) Outcome type: general notes on side effects
Identification	Sponsorship source: NA Country: US Setting: inpatient, single‐centre Author's name: Ray McKenzie Institution: Department of Anesthesiology, Magee‐Womens Hospital, Pittsburgh, PA, USA Email: NA Address: 300 Halket Street, Pittsburgh, PA 15213, USA Language: English Duration of study: NA Trial registry number: NA Study's primary outcome: complete response, defined as no emesis and no administration of rescue antiemetic medication during the 24‐hour postoperative period
Notes	None
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "...each ml of blood lost. The patients were stratified by a positive or negative history of PONV with previous surgery to assure an equal number of patients (n = 20) in each subgroup. After induction of anesthesia and when the patient was stable, ondansetron 4 mg IV was given. Identical syringes of saline (Group 1) or dexamethasone 20 mg (Group 2) were prepared via random number table assignment by personnel not involved in the study. The unknown study drug was administered..."
Allocation concealment (selection bias)	Low risk	Quote: "...4 mg IV was given. Identical syringes of saline (Group 1) or dexamethasone 20 mg (Group 2) were prepared via random number table assignment by personnel not involved in the study. The unknown study drug was administered IV..." Judgement comment: participants and investigators could not foresee assignment (random number table and syringes generated by personnel not involved in the study)
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "after induction of anesthesia and when the patient was stable, ondansetron 4 mg IV was given. Identical syringes of saline (Group 1) or dexamethasone 20 mg (Group 2) were prepared via random number table assignment by personnel not involved in the study. The unknown study drug was administered IV after confirming no change in vital signs. The 24hour study duration began..."
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Judgement comment: no statement on blinding of outcome assessors
Incomplete outcome data (attrition bias) All outcomes	Low risk	Judgement comment: no missing outcome data
Selective reporting (reporting bias)	Unclear risk	Judgement comment: no reference to a study protocol or trial registry number reported
Other bias	Unclear risk	Judgement comment: baseline characteristics (age, weight): no; (ASA): unclear. Potential effect modifiers (gender, duration of anaesthesia, history of PONV/motion sickness, perioperative opioids): no; (non‐smoker): unclear