Blackard 1972.

Methods	Study design: parallel‐group, double‐blind randomized trial Study dates: 1 January 1969 to 31 December 1969 Setting: 1 hospital Country: USA
Participants	Inclusion criteria: no fever or clinical UTI; required no antibacterial agents during the preceding 2 weeks; no retention type urethral catheter; no need for immediate operation; no allergy to sulphonamide Exclusion criteria: not available Sample size: 75 men Age (years): overall median 74 (44–82) Sex: all men
Interventions	Group 1 (n = 37): placebo, oral, started 2 days before cystoscopy and maintained 10 days following cystoscopy Group 2 (n = 38): sulphamethoxazole 500 mg + phenazopyridine 100 mg, oral, started 2 days before cystoscopy and maintained 10 days following cystoscopy
Outcomes	Systemic UTI How measured: body temperature ≥ 38 °C Time points measured: within 10 days after cystoscopy Time points reported: within 10 days after cystoscopy Outcomes: placebo group: 0/37 participants had fever 1 day after cystoscopy, and 5/37 had fever within 2–10 days after cystoscopy; treatment group: 4/38 had fever 1 day after cystoscopy, and 5/38 had fever within 2–10 days after cystoscopy Bacteriuria How measured: urine culture yielded > 104 CFU/mL Time points measured: within 10 days after cystoscopy Time points reported: within 10 days after cystoscopy Outcomes: placebo group: 17/37 participants had bacteriuria 1 day after cystoscopy, and 14/37 had bacteriuria within 2–10 days after cystoscopy; treatment group: 6/38 had bacteriuria 1 day after cystoscopy, and 5/38 had bacteriuria within 2–10 days after cystoscopy Minor adverse events How measured: decided by physician Time points measured: within 10 days after cystoscopy Time points reported: within 10 days after cystoscopy Outcomes: treatment group: 1 participants had drug eruption and 2 participants had sulphonamide crystals in the urine 1 day after cystoscopy
Funding sources	No information about funding
Declarations of interest	No information about conflict and interest
Notes	For participants with sterile urine before cystoscopy, in the placebo group, 7/27 had bacteriuria 1 day after cystoscopy, and 6/27 had bacteriuria within 2–10 days after cystoscopy. In the treatment group, 3/27 had bacteriuria 1 day after cystoscopy, and 3/27 had bacteriuria within 2–10 days after cystoscopy Localized symptom How measured: burning or painful urination usually accompanied by frequency and urgency Time points measured: within 10 days after cystoscopy Time points reported: within 10 days after cystoscopy Outcomes: placebo group: 16/37 participants had localized symptom 1 day after cystoscopy, and 9/37 had localized symptom within 2–10 days after cystoscopy; treatment group: 16/38 had localized symptom 1 day after cystoscopy, and 11/38 had localized symptom within 2–10 days after cystoscopy No email address available for contacting the corresponding author for further information.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Drugs were randomly assigned and administered in a double‐blind fashion." Comment: method for generation of random sequence not given.
Allocation concealment (selection bias)	Unclear risk	Comment: no information regarding the concealment of randomization.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "Drugs and placebo looked like the same and they were randomly assigned to participants, principle investigator and participants were not able to identify the active drugs or placebo." Comment: treatment providers and participants adequately blinded.
Blinding of outcome assessment (detection bias) Subjective outcomes	Low risk	Quote: "Drugs were randomly assigned and administered in a double‐blind fashion." Comment: double‐blind study, and this probably done.
Blinding of outcome assessment (detection bias) Objective outcomes	Unclear risk	Comment: not applicable, since the objective outcome of drug resistance was not reported.
Incomplete outcome data (attrition bias) Systemic UTI	Low risk	Quote: "In the placebo group, none of 37 had fever 1 day after cystoscopy, and 5 out of 37 had fever within 2 to 10 days after cystoscopy. in the treatment group, 4 out of 38 had fever 1 day after cystoscopy, and 5 out of 38 had fever within 2 to 10 days after cystoscopy (rephrased from table)." Comment: 75/75 randomized participants (37 participants in the control arm, 38 participants in the intervention arm) were included for analysis of this outcome.
Incomplete outcome data (attrition bias) Symptomatic UTI	Low risk	Quote: "In the placebo group, 17 out of 37 had bacteriuria 1 day after cystoscopy, and 14 out of 37 had bacteriuria within 2 to 10 days after cystoscopy. In the treatment group, 6 out of 38 had bacteriuria 1 day after cystoscopy, and 5 out of 38 had bacteriuria within 2 to 10 days after cystoscopy (rephrased from table)." Comment: 75/75 randomized participants (37 participants in control arm, 38 participants in intervention arm) were included for analysis of this outcome.
Incomplete outcome data (attrition bias) Serious adverse events	Low risk	Quote: "In the treatment group, 1 participants had drug eruption and 2 participants had sulfenamide crystals in the urine 1 day after cystoscopy (rephrased from table)." Comment: 75/75 randomized participants (37 participants in control arm, 38 participants in intervention arm) were included for analysis of this outcome.
Incomplete outcome data (attrition bias) Minor adverse events	Low risk	Quote: "In the treatment group, 1 participants had drug eruption and 2 participants had sulfenamide crystals in the urine 1 day after cystoscopy (rephrased from table)." Comment: 75/75 randomized participants (37 participants in control arm, 38 participants in intervention arm) were included for analysis of this outcome.
Incomplete outcome data (attrition bias) Localized UTI	Unclear risk	Comment: outcome not reported.
Incomplete outcome data (attrition bias) Asymptomatic bacteriuria	Unclear risk	Comment: outcome not reported (bacteriuria was reported, but without differentiating whether participants had symptoms or not).
Incomplete outcome data (attrition bias) Bacterial resistance	Unclear risk	Comment: outcome not reported.
Selective reporting (reporting bias)	Unclear risk	Comment: data reported on all outcomes specified in methods section, but there was no access to trial protocol/registration to further assess selective reporting.
Other bias	Low risk	Comment: no other bias detected.