Severe hyponatremia due to trimethoprim-sulfamethoxazole: a case report

Hyponatremia, a prevalent electrolyte imbalance with varying degrees of severity, can lead to mild to severe complications. Trimethoprim-sulfamethoxazole (TMP-SMX) and spironolactone are two frequently administered medications; regrettably, most healthcare professionals are not aware that these medications might cause hyponatremia. Concurrently, the two drugs have a high chance of medication interactions that raise the risk of hyponatremia, hyperkalemia, and death overall. TMP-SMX is implicated in causing hyponatremia through diverse mechanisms, such as inhibiting the renal tubular epithelial enzyme carbonic anhydrase. Structurally akin to the potassium-sparing diuretic amiloride, TMP-SMX is linked to hyperkalemia and hyponatremia by obstructing epithelial sodium channels in the distal nephron. Moreover, TMP-SMX may enhance antidiuretic hormone (ADH) release, exacerbating the imbalance.

This is a case of a 76-year-old man with a medical history including hypertension, type II diabetes, coronary artery disease, and dyslipidemia. This case highlights an elderly patient treated with TMP-SMX for a soft tissue wound infection, which resulted in severe hyponatremia.

Timely identification and careful monitoring of TMP-SMX-induced hyponatremia enabled the correction of sodium levels without severe complications. Thus, this report underscores the importance of vigilant monitoring and prompt identification of hyponatremia in patients undergoing TMP-SMX treatment. Further research is warranted due to limited data on the precise mechanisms of TMP-SMX-induced hyponatremia.