Adverse Outcome Risks With Trimethoprim After UTI in Older Adults

Treatment of urinary tract infections (UTIs) with trimethoprim was associated with greater risk for kidney injury and hyperkalemia compared with other antibiotics, but not a greater risk for death, according to research published in the British Medical Journal.

Between April 1997 and September 2015, using electronic primary care records, adults aged ≥65 years with a prescription for trimethoprim, amoxicillin, cephalexin, ciprofloxacin, or nitrofurantoin up to 3 days after a primary care diagnosis of UTI were included in a cohort study.

A total of 422,514 episodes of UTI treated with antibiotics were included. Results showed that up to 14 days after the commencement of treatment, the odds of acute kidney injury were higher after trimethoprim (adjusted odds ratio [aOR], 1.72; 95% CI, 1.31-2.24) and ciprofloxacin (aOR 1.48; 95% CI, 1.03-2.13) compared with amoxicillin.

The odds of hyperkalemia were only higher after trimethoprim (aOR, 2.27; 95% CI, 1.49-3.45) compared with amoxicillin. The odds of death were not higher with trimethoprim compared with amoxicillin; however, for those taking renin-angiotensin system blockers, the odds of death were 1.12 (95% CI, 0.80-1.57).

These results indicate that for every 1000 UTIs treated in this population, using trimethoprim instead of amoxicillin would result in 1 to 2 additional cases of hyperkalemia and 2 admissions with acute kidney injury, and this would increase to 18 cases and 11 admissions for those taking renin-angiotensin system blockers and spironolactone treatment, respectively.

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Investigators concluded that “for groups at high risk of acute kidney injury and hyperkalaemia, other antibiotics should be considered, but, if this is not possible, monitoring of renal function and potassium levels should be performed.”


Crellin E, Mansfield KE, Leyrat C, et al. Trimethoprim use for urinary tract infection and risk of adverse outcomes in older patients: cohort studyBMJ. 2018;360:k341.