TMP-SMX linked to increased risk of hyperkalemia in the elderly

Older adults simultaneously taking beta-blockers and trimethoprim-sulfamethoxazole (TMP-SMX), widely prescribed for urinary tract infections, appeared to be more at risk for hyperkalemia requiring hospitalization than their cohorts taking beta-blockers and amoxicillin, according to the results of 2 nested case-control studies out of Canada.

Researchers studied data from a cohort of almost 300,000 adults aged 66 years or older assembled from these studies.

During the study period of 1994 to 2008, 189 patients were hospitalized for hyperkalemia within 2 weeks of receiving a study antibiotic.

Further, the effect was dose-dependent: the higher the dose of TMP-SMX, the greater the risk. No such risk was identified with ciprofloxacin, norfloxacin, or nitrofurantoin.

The study was conducted largely because the researchers surmised that the concurrent use of beta-blockers was the cause of the higher risk of severe hyperkalemia in older TMP-SMX users. However, a similarly increased risk was found among older adults not taking beta-blockers.

Study researchers then concluded that no added risk exists when TMP-SMX is used in combination with beta-blockers.

Weir MA, Juurlink DN, Gomes T, et al. Beta-blockers, trimethoprim-sulfamethoxazole, and the risk of hyperkalemia requiring hospitalization in the elderly: a nested case-control study. Clin J Am Soc Nephrol. 2010. Epub ahead of print.