Dobkin 1968.

Study characteristics
Methods	Study design: randomized controlled trial Study grouping: 3 groups, monoprophylaxis
Participants	Baseline characteristics Placebo Assessed for eligibility (n): ‐ Enrolled (n): ‐ Randomized (n): 94 Received treatment (n): NA Analysed (n): 94 Age (mean ± SD, median (IQR), median (range)): NA Weight (mean ± SD, median (IQR), median (range)): NA BMI (mean ± SD, median (IQR), median (range)): NA ASA I/II/III/IV (n): NA Gender (female in %): 50 Non‐smoker (%): NA History of PONV/motion sickness (%): NA Type of general anaesthesia: inhalational anaesthesia (methoxyflurane, N₂O) Duration of anaesthesia or surgery (in min; as mean or median): NA Use of perioperative opioids (if yes, which?): NA Type of surgery: major upper abdominal operations Metoclopramide Assessed for eligibility (n): ‐ Enrolled (n): ‐ Randomized (n): 96 Received treatment (n): NA Analysed (n): 96 Age (mean ± SD, median (IQR), median (range)): NA Weight (mean ± SD, median (IQR), median (range)): NA BMI (mean ± SD, median (IQR), median (range)): NA ASA I/II/III/IV (n): NA Gender (female in %): 62.5 Non‐smoker (%): NA History of PONV/motion sickness (%): NA Type of general anaesthesia: inhalational anaesthesia (methoxyflurane, N₂O) Duration of anaesthesia or surgery (in min; as mean or median): NA Use of perioperative opioids (if yes, which?): NA Type of surgery: major upper abdominal operations Trimethobenzamide Assessed for eligibility (n): ‐ Enrolled (n): ‐ Randomized (n): 94 Received treatment (n): NA Analysed (n): 94 Age (mean ± SD, median (IQR), median (range)): NA Weight (mean ± SD, median (IQR), median (range)): NA BMI (mean ± SD, median (IQR), median (range)): NA ASA I/II/III/IV (n): NA Gender (female in %): 55.32 Non‐smoker (%): NA History of PONV/motion sickness (%): NA Type of general anaesthesia: inhalational anaesthesia (methoxyflurane, N₂O) Duration of anaesthesia or surgery (in min; as mean or median): NA Use of perioperative opioids (if yes, which?): NA Type of surgery: major upper abdominal operations Included criteria: adult patients, elective cases scheduled for major upper abdominal operations Excluded criteria: NA Pretreatment: baseline characteristics (age): no; (weight, ASA): unclear. Potential effect modifiers (gender, duration of anaesthesia): no; (history of PONV/motion sickness, non‐smoker, perioperative opioids): unclear
Interventions	Intervention characteristics Placebo Dose: lactose Time point of administration: approximately 30 minutes before end of each operation Route of administration: IV Rescue antiemetics (if yes, which?): NA Metoclopramide Dose: 20 mg Time point of administration: approximately 30 minutes before end of each operation Route of administration: IV Rescue antiemetics (if yes, which?): NA Trimethobenzamide Dose: 300 mg Time point of administration: approximately 30 minutes before end of each operation Route of administration: IV Rescue antiemetics (if yes, which?): NA
Outcomes	Nausea (0 to 24 hours) Outcome type: dichotomous outcome
Identification	Sponsorship source: this project was supported by a grant‐in‐aid from Merck Sharp Dohme Research Laboratories Country: USA Setting: inpatient, single‐centre Author's name: Allen B. Dobkin Institution: Department of Anesthesiology, State University Hospital, State University of New York, Upstate Medical Center, Syracuse, New York, NY, USA Email: NA Address: NA Duration of study: NA Language: English Study's primary outcome: NA Trial registry number: NA
Notes	None
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "the order of assignment of the drugs followed a random number code"
Allocation concealment (selection bias)	Unclear risk	Quote: "the order of assignment of the drugs followed a random number code. The identity of the substance was not known to the anaesthetist, who merely recorded the code number of the drug on his anaesthetic record after he administered the material" Judgement comment: no details on allocation provided
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "the identity of the substance was not known to the anaesthetist"
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "the patient's chart was reviewed 24 hours postoperatively to record the incidence of nausea and vomiting and related information. The identity of the compounds administered was not revealed to the principals involved in the study until the study was completed and all the data were tabulated"
Incomplete outcome data (attrition bias) All outcomes	Low risk	Quote: "each patient's record was reviewed 24 hours after the operation to obtain follow‐up data" 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): no; (weight, ASA): unclear. Potential effect modifiers (gender, duration of anaesthesia): no; (history of PONV/motion sickness, non‐smoker, perioperative opioids): unclear