Trimethoprim Urine Excretion and Its Potential for Treating Canine Urinary Tract Infections

Antimicrobial resistant urinary tract infections (UTI) in dogs are becoming more common, and treatment options can be limited. Sulfonamide antimicrobials, often in combination with trimethoprim, can be used. However, sulfonamides may produce severe adverse effects in dogs, including death. Trimethoprim, without a sulfonamide, is routinely used in humans for UTI. Our objective was to evaluate trimethoprim urine concentrations in dogs after a single oral trimethoprim dose. We hypothesized trimethoprim can sustain urine concentrations that may be effective for treating canine UTI. Our Institutional Animal Care and Use Committee approved the study. Nine healthy client-owned dogs of varying breeds received a single oral dose of trimethoprim 5 mg/kg. Clients collected urine (free catch) before trimethoprim administration and then at 6-, 8-, 12-, and 24-h post administration. Trimethoprim urine concentrations were analyzed via validated mass spectrometry. The range of urine concentrations at 6 h (69.9-413 mcg/mL), 8 h (46.2-405 mcg/mL), 12 h (34.5-220 mcg/mL) and 24 h (17.2-154 mcg/mL) all exceeded 8 mcg/mL, the susceptible breakpoint for Enterobacterales UTI in human patients. However, specific breakpoints and pharmacodynamics in dogs have not been reported. These data suggest oral trimethoprim may be effective for canine Enterobacterales UTI. Further research is needed to confirm the clinical efficacy of trimethoprim in canine UTI.