NEW YORK (Reuters Health) — Elderly women who were treated for urinary tract infections with trimethoprim-sulfamethoxazole were 3 times more likely to be hospitalized for hyperkalemia in the 10 days following than those treated with amoxicillin, according to new research. The authors say that the findings should encourage doctors to consider options besides TMP-SMX, especially in treating patients who may have kidney risks, or to monitor those that are prescribed TMP-SMX for the changes in potassium levels that are characteristic of hyperkalemia.

In the study, published as letter to the editor in the American Journal of Kidney Diseases, Canadian researchers retrospectively analyzed Ontario health care databases, including the Ontario Drug Benefit database, for women over 65 who were prescribed a single antibiotic during an outpatient visit for a simple UTI. In total, the study included 393,039 women who were treated between 1997 and 2009.

Records showed that doctors prescribed women TMP-SMX (n = 87,569), ciprofloxacin (n = 59,239), norfloxacin (n = 117,732), nitrofurantoin (n = 11363,972) and amoxicillin (n = 24,527). Baseline creatinine levels were only available for a minority of patients, but the levels that were available suggested that for the most part patients had fairly normal kidney function, said Dr. Ngan Lam, the study