Trimethoprim is an antibiotic medication used mainly to treat urinary tract infections (UTI). Some studies suggest that the use of trimethoprim for UTI in older adults could increase the risk of adverse health outcomes. This study aims to evaluate the adverse effects of trimethoprim use for UTI in older adults.

This cohort study included a cohort of 422,514 patients aged 65 and above with UTI who underwent at least one antibiotic treatment. The eligible patients underwent a prescription of the following antibiotics: trimethoprim, cefalexin, ciprofloxacin, amoxicillin, and nitrofurantoin. The primary outcome of the study was acute kidney injury, hyperkalemia, and mortality within 14 days of antibiotic treatment for UTI.

The risk of acute kidney injury in the first 14 days following the antibiotic treatment was the highest with trimethoprim (adjusted odds ratio 1.72), followed by ciprofloxacin (1.48). The OR of hyperkalemia was only higher with trimethoprim (aOR 2.27) compared with other antibiotics. The odds of mortality, however, were not higher in trimethoprim when compared with amoxicillin and ciprofloxacin.

The research concluded that trimethoprim was associated with a significantly greater risk of acute kidney injury and hyperkalemia compared with amoxicillin and ciprofloxacin, but not with a higher risk of mortality.