Placebo is non-inferior to postoperative antimicrobial treatment in uncomplicated canine pyometra - A double-blinded...

Postoperative antimicrobial therapy is frequently administered after surgical treatment for pyometra in dogs, despite limited evidence supporting its necessity in uncomplicated cases. Antimicrobial resistance concerns call for re-evaluation of such practices. This randomized, double-blinded, placebo-controlled, non-inferiority clinical trial was conducted on client-owned dogs at the Veterinary Teaching Hospital of the University of Helsinki. All dogs received perioperative sulfadoxine-trimethoprim prophylaxis and were then randomized to receive either placebo or a five-day course of oral sulfadiazine-trimethoprim as active control. The primary outcome was the incidence of surgical site infections (SSI) within 30 days; the secondary outcome was the incidence of clinical urinary tract infections (UTI) within 12 days. The non-inferiority margins were set at 7 % (SSI) and 15 % (UTI). Infection outcomes were assessed in both the intention-to-treat (ITT) and per-protocol populations (PP). A total of 152 dogs were included. In the ITT population, SSI incidence was 2.7 % in the placebo group and 7.8 % in the sulfadiazine-trimethoprim group, with an absolute difference of -5.1 % (CI_95 %: -13.6-2.8 %). UTI incidence was 0 % in the placebo group and 3.9 % in the sulfadiazine-trimethoprim group (difference -7.7 %, CI_95 %: -24.1-8.2 %). Results in the PP were similar. All findings supported the non-inferiority of placebo. A single perioperative dose of sulfadoxine-trimethoprim appears sufficient for preventing postoperative infections in this low-risk surgical population.