TRIMETHOPRIM-SULFAMETHOXAZOLE INDUCES REVERSIBLE HYPERKALEMIA

Objective: To determine the effect of trimethoprim-sulfamethoxazole (T mp-Smx) on serum potassium concentration. Design: Retrospective cohort study. Setting: An urban teaching hospital. Patients: Fifty-one perso ns hospitalized for symptomatic infection with human immunodeficiency virus (HIV). Twenty-five patients who were taking high-dose Tmp-Smx (t rimethoprim 20 mg/kg per day; sulfamethoxazole, 100 mg/kg per day) for Pneumocystis carinii pneumonia were the study group. Twenty-six patie nts who had not received the drug were the control group. Patients who received potassium supplements, those taking medications known to alt er potassium homeostasis or renal function, or those with a serum crea tinine level more than 186 mumol/L were excluded. Measurements and Mai n Results: Serum potassium concentration in the study group was 4.1 +/ - 0.1 mmol/L (mean +/- SE) and increased by 1.1 mmol/L (CI, 0.8 to 1.5 mmol/L) (P < 0.0001) 9.8 +/- 0.5 days after starting Tmp-Smx therapy. Patients followed longitudinally showed a progressive increase in ser um potassium levels during therapy and a progressive decline after dis continuing Tmp-Smx. Blood urea nitrogen and serum creatinine levels in creased mildly from 4.3 +/- 0.5 mmol/L and 85 +/- 6 mumol/L to 6.4 +/- 0.7 mmol/L and 113 +/- 8 mumol/L, respectively. The serum potassium l evel in the control group was 4.3 +/- 0.1 mmol/L and remained unchange d during hospitalization. Conclusions: High-dose Tmp-Smx therapy used for the treatment of P. carinii pneumonia in HIV-infected patients lea ds to an increase in the serum potassium concentration and may result in life-threatening hyperkalemia. Patients receiving high doses of Tmp -Smx require close monitoring of their serum potassium concentration, particularly 7 to 10 days after the start of therapy.