Bacic 1998.

Study characteristics
Methods	Study design: randomized controlled trial Study grouping: 2 groups, monoprophylaxis
Participants	Baseline characteristics Ondansetron Assessed for eligibility (n): ‐ Enrolled (n): ‐ Randomized (n): 25 Received treatment (n): 25 Analysed (n): 24 (secondary publication) Age (mean ± SD, median (IQR), median (range)): 32.9 ± 3.1 (all groups combined) Weight (mean ± SD, median (IQR), median (range)): 65.5 ± 2.6 (all groups combined) BMI (mean ± SD, median (IQR), median (range)): NA ASA I/II/III/IV (n): NA Gender (female in %): 100 Non‐smoker (%): NA History of PONV/motion sickness (%): NA Type of general anaesthesia: Balanced anaesthesia (fentanyl, N₂O) Duration of anaesthesia or surgery (in min; as mean or median): 52.8 ± 6.2 (all groups combined) Use of perioperative opioids (if yes, which?): fentanyl for anaesthesia Type of surgery: unilateral thyroid surgery Placebo Assessed for eligibility (n): ‐ Enrolled (n): ‐ Randomized (n): 25 Received treatment (n): 25 Analysed (n): 21 (secondary publication) Age (mean ± SD, median (IQR), median (range)): 32.9 ± 3.1 (all groups combined) Weight (mean ± SD, median (IQR), median (range)): 65.5 ± 2.6 (all groups combined) BMI (mean ± SD, median (IQR), median (range)): NA ASA I/II/III/IV (n): NA Gender (female in %): 100 Non‐smoker (%): NA History of PONV/motion sickness (%): NA Type of general anaesthesia: balanced anaesthesia (fentanyl, N₂O) Duration of anaesthesia or surgery (in min; as mean or median): 52.8 ± 6.2 (all groups combined) Use of perioperative opioids (if yes, which?): fentanyl for anaesthesia Type of surgery: unilateral thyroid surgery Included criteria: female patients, 18 to 45 years of age, regular menstrual periods, scheduled for elective unilateral thyroid surgery Excluded criteria: patients with irregular cycles, those using oestrogen or progestogen drugs, persons with a positive history of earlier postoperative nausea and vomiting or motion sickness Pretreatment: baseline characteristics (age, weight, ASA): no. Potential effect modifiers (gender, history of PONV/motion sickness): no; (duration of anaesthesia, non‐smoker, perioperative opioids): unclear
Interventions	Intervention characteristics Ondansetron Dose: 8 mg Time point of administration: 30 minutes before anaesthesia induction Route of administration: IV Rescue antiemetics (if yes, which?): NA Placebo Dose: saline Time point of administration: 30 minutes before anaesthesia induction Route of administration: IV Rescue antiemetics (if yes, which?): NA
Outcomes	PONV (0 to 24 hours) Outcome type: dichotomous outcome Headache (0 to 24 hours) Outcome type: dichotomous outcome Constipation (0 to 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: Croatia Setting: inpatient, single‐centre Author's name: Zvonko Rumboldt Institution: Department of Medicine, University of Split School of Medicine, Croatia Email: NA Address: Department of Medicine, University of Split School of Medicine, 21000 Split, Spinciceva 1, Croatia Duration of study: NA Language: English Study's primary outcome: NA Trial registry number: NA
Notes	Two studies. Only 1 study was randomized. Secondary publication available (data inconsistent with the primary report)
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Judgement comment: quote: "these women received randomly" No information on sequence generation provided
Allocation concealment (selection bias)	Unclear risk	Judgement comment: quote: "...following instructions in sealed envelopes" Not stated sequentially numbered, opaque, sealed envelopes (SNOSE)
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Judgement comment: no statement on blinding of participants and personnel
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	Unclear risk	Judgement comment: 5 dropouts (1 in the ondansetron group and 4 in the placebo group; refused to gauge postoperative nausea and vomiting intensity). Data from the secondary publication were used because data are consistent but are different from the primary reference (Bacic 2000)
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, ASA): no. Potential effect modifiers (gender, history of PONV/motion sickness): no; (duration of anaesthesia, non‐smoker, perioperative opioids): unclear