An unexpected cause of hyponatremia in a cancer patient: Trimethoprim-sulfamethoxazole

Abstract: Background Hyponatremia is one of the most common electrolyte abnormalities seen in hospitalized patients. In cancer patients, it's generally related to syndrome of inappropriate ADH secretion (SIADH). Case Report Here, we report a breast cancer patient with hyponatremia related to high dose trimethoprim-sulfamethoxazole use for pneumonitis cariini pneumonia. Conclusion It is important to be aware that all hyponatremias are not related to SIADH in cancer patients. For proper treatment strategies, a proper differential diagnosis is needed.