Plasma Potassium Concentration Changes Associated with Trimethoprim used for Urinary Tract Infections

Abstract

Background: Hyperkalaemia has been reported with highdose trimethoprim (20 mg/kg/day) and standard-dose trimethoprim (6 mg/kg/day) plus sulfamethoxazole use. Aim: To investigate changes in plasma potassium concentrations in patients prescribed standard-dose trimethoprim 300 mg daily for urinary tract infections. Method: A retrospective cohort study of hospital patients with urinary tract infections treated with trimethoprim or other antibacterials (control group) for more than 5 days. Plasma potassium concentration, creatinine and urea were compared at baseline and at the completion of treatment. Results: There were 31 patients in the trimethoprim group and 65 patients in the control group. End-of-therapy mean plasma potassium concentrations increased significantly from baseline in the trimethoprim group (4.2 ± 0.4 mmol/L to 4.5 ± 0.5 mmol/L; p = 0.002) but not in the control group. End-oftherapy mean plasma potassium concentrations were also higher in the trimethoprim group (4.5 ± 0.5 mmol/L vs 4.2 ± 0.5 mmol/L; p = 0.007). 65% of the trimethoprim group developed end-of-therapy hyperkalaemia versus 39% of the control group. Mean creatinine concentration in the trimethoprim group increased by an average of 21% from baseline but did not change in the control group. The trimethoprim group showed no change in mean urea concentration but a decrease was noted in the control group. Conclusion: Treating urinary tract infections with trimethoprim 300 mg daily for more than 5 days was associated with an increase in plasma potassium concentration.