Case report: reversible hyperkalemia associated with trimethoprim- sulfamethoxazole.

Trimethoprim-sulfamethoxazole (TMP-SMX) is a fixed-dose antimicrobial agent used in a variety of infections. Adverse reactions are more common in patients with AIDS, but occasionally occur in immunocompetent patients. Renal toxicity is usually a hypersensitivity reaction to the sulfa component, and manifests as interstitial nephritis or sulfa crystallization in the renal tubules. Reversible hyperkalemia is a rarely reported side effect of TMP-SMX therapy attributed to TMP inhibition of potassium secretion in the distal renal tubule in a manner similar to the potassium sparing diuretic, amiloride. In this article, the author reports a case of hyperkalemia associated with TMP-SMK occurring in an elderly man with no other risk factors for hyperkalemia, which resolved upon discontinuation of the drug.