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Hyperkalemia in Elderly Patients Receiving Standard Doses of Trimethoprim-Sulfamethoxazole
- Heino Velazquez, PhD; and
- David H. Ellison, MD
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IN RESPONSE:
We agree with Drs. Canaday and Johnson that trimethoprim may cause hyperkalemia, even at lower doses. As we reported [1], the dose-response curve for trimethoprim on the lumen-negative voltage in the distal tubule indicated an effective concentration range greater than one order of magnitude. A maximal effect was obtained at a luminal concentration of approximately 1 mM (the approximate concentration achieved in urine when patients receive a single trimethoprim dose of 200 mg). However, a tenfold lower dose achieved half the maximal response, suggesting effective blockade of sodium channels and potassium secretion. Thus, trimethoprim given at a lower dose (6.5 mg/kg per day compared with 20 mg/kg per day) or at greater intervals (twice daily compared with daily) can result in hyperkalemia. Biological responses and predisposing factors may also determine whether hyperkalemia develops (for example, plasma potassium >5.0 mmol/L). In most patients treated with trimethoprim, serum potassium concentrations increased, even though peak values exceed 5 mmol/L in only 50% of patients.
Heino Velazquez, PhD
David H. Ellison, MD
Yale University School of Medicine; 333 Cedar Street, 2074 LMP; New Haven, CT 06502-8029
The Editors welcome submissions for possible publication in the Letters section. Authors of letters should:
•Include no more than 300 words of text, three authors, and five references
•Type with double-spacing
•Send three copies of the letter, an authors' form signed by all authors, and a cover letter describing any conflicts of interest related to the contents of the letter.
Letters commenting on an Annals article will be considered if they are received within 6 weeks of the time the article was published. Only some of the letters received can be published. Published letters are edited and may be shortened; tables and figures are included only selectively. Authors will be notified that the letter has been received. If the letter is selected for publication, the author will be notified about 3 weeks before the publication date. Unpublished letters cannot be returned.
Annals welcomes electronically submitted letters.
- Copyright ©2004 by the American College of Physicians
