TMP-SMX Associated With Hyperkalemia in Elderly

Concomitant use of β-blockers does not appear to add to risk
By Lindsey Marcellin
HealthDay Reporter

FRIDAY, July 2 (HealthDay News) -- Older patients taking trimethoprim-sulfamethoxazole (TMP-SMX) have a substantially increased risk of hyperkalemia requiring hospitalization, but being on β-blockers does not further increase this risk, according to research published online July 1 in the Clinical Journal of the American Society of Nephrology.

Matthew A. Weir, M.D., of the University of Western Ontario in London, Canada, and colleagues conducted a nested case-control study using health administrative databases from Ontario to examine the association of the use of TMP-SMX and hospitalization for hyperkalemia in older patients on β-blockers. A cohort of 299,749 patients aged 66 and older on β-blockers was used.

During the study period (1994 to 2008), the researchers found that 189 of the patients were hospitalized for hyperkalemia within 14 days of receiving an antibiotic. The patients who had been prescribed TMP-SMX had an adjusted odds ratio of 5.1 for admission for hyperkalemia, compared to those who were prescribed amoxicillin -- an association which was stronger at higher doses of TMP-SMX. There were no significant associations found between hospitalization for hyperkalemia and use of norfloxacin, ciprofloxacin, or nitrofurantoin. When repeating the analysis with a new patient cohort not taking β-blockers, results were not significantly different.

"The role of β-blockers in hyperkalemia among elderly ambulatory patients may not be as great as originally anticipated. We recognize the importance of TMP-SMX in the modern antibiotic armamentarium and do not suggest curtailing its use. Rather, it is likely that some cases of severe morbidity associated with TMP-SMX may be prevented through simple measures such as serum potassium testing. In this analysis, only a small proportion of patients had such testing in the days following TMP-SMX prescription," the authors write.

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