Abstract: Objective To explore the cause of hyponatremia and hyperkalemia induced by combined medication of Trimethoprim-sulfamethoxazole(SMZ co) and follow-up treatment. Methods An old female patient with long-term spironolactone use took SMZ co for urinary tract infection and then developed hyponatremia and hyperkalemia. The process of diagnosis and treatment was analyzed based on literature retrieval. Results The patient presented with nausea and dyspnea, accompanied hyponatremia, hyperkalemia and renal deterioration after initiating SMZ co for 6 days. Symptomatic and supportive treatment were implemented immediately including withdrawal of spironolactone, reducing dosage of SMZ co, diuresis, electrolyte correction, urine alkalinization etc. Furthermore Blood potassium and sodium gradually returned to normal, creatinine level decreased. Conclusion High basal creatinine levels combined with potassium-preserving diuretics are risk factors for adverse drug reactions. Attention should be paid to the influence of drug interaction, especially in patients with renal dysfunction. It is recommended to closely monitor electrolytes and renal function, reduce or stop medicaition if necessary. Baseline high serum creatinine, and co-administration of spironolacone may contribute to these ADR.

Key words: Trimethoprim-sulfamethoxazole, hyponatremia, hyperkalemia, renal dysfunction