Britt 1977.

Methods	Placebo‐controlled RCT
Participants	215 female patients entered into the study and randomised Inclusion criteria: Undergoing elective gynaecological surgery and who received a urinary catheter or supra‐pubic catheter at the time of surgery for at least one day Exclusion criteria: Rapidly or ultimately fatal disease, active clinical infection, allergy to penicillins or cephalosporins Losses post randomisation:
Interventions	Group 1 (n = 96): Cefazolin sodium 500 mg was given at the time of operation, and each subsequent dose was given at 8‐hour intervals, IV or IM, for a total of nine doses (= three days). Group 2 (n = 100): Placebo was given at the time of operation, and each subsequent dose was given at 8‐hour intervals, IV or IM, for a total of nine doses (= three days).
Outcomes	Bacteriuria during period of antibiotic prophylaxis (days 1‐3) (102> CFU/mL for urinary catheter and 105> CFU/mL for MSU): Group 1 1/96 Group 2 9/100 Secondary outcomes: febrile morbidity, catheter days, types of organisms
Notes	A urine sample was obtained at the time of catheter insertion and daily from the drainage tube. A clean‐voided specimen was taken on discharge when the catheter was already removed. Remark: Group 1: 6 supra pubic/90 urinary catheters (0.07) Group 2: 12 supra pubic/88 urinary catheters (0.14)
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Hospital pharmacy provided a randomisation schedule.
Allocation concealment (selection bias)	Low risk	Hospital pharmacy provided a randomisation schedule.
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Quote "Neither the attending physicians, study personnel, nor nursing personnel were aware of the treatment regime assigned by the pharmacy". Blinding by patients not stated.
Incomplete outcome data (attrition bias) All outcomes	Low risk	8.8% attrition (19 patients were excluded: 14 patients were bacteriuric at the time of catheter insertion, five patients were catheterised for less than one day).
Selective reporting (reporting bias)	Unclear risk	Reports all prespecified outcomes but we were unable to access the trial protocol.
Incomplete outcome data (ITT analysis)	High risk	No ITT analysis stated.
Timing of outcome assessment similar in all groups	Low risk	All participants assessed on third day.
Other bias	Unclear risk	Public Health Service grant plus a grant for Ely Lilly & Co. Indianapolis, Ind.