Trimethoprim-sulfamethoxazole Induced Hypornatremia and Hyperkalemia, The Necessity of Electrolyte Follow-up in Every Patient

Trimethoprim-sulfamethoxazole (TMP/SMX) is a bactericidal antibiotic. The most common adverse effect of TMP/SMX is skin rashes and gastrointestinal symptoms. Although hyperkalemia can occur with TMP/SMX component but hyponatremia is uncommon. A 55- year old woman, known case of rheumatoid arthritis, presented with fever and mild dyspnea. According to diagnostic work up the infection with pneumocystis jirovecii was confirmed. TMP/ SMX was started but after 10 days the patient acutely represented with nausea and became lethargic. The laboratory studies showed moderate hyperkalemia and severe hyponatremia. TMP/SMX was stopped and alternative treatment started. Upon discontinuation of the drug, serum sodium and potassium levels were both changed to normal. Hyponatremia as a life threatening adverse effect appears to be rare with TMP–SMX therapy, but clinicians should be aware of electrolyte disturbances developed with this drug and electrolyte monitoring should always be considered.