REPLY
Hyperkalemia in Elderly Patients Receiving Standard Doses of Trimethoprim-Sulfamethoxazole
Ira W. Reiser, MD, and
Shyan-Yih Chou, MD
1 March 1994 | Volume 120 Issue 5 | Pages 437-438
IN RESPONSE:
Before receiving the above correspondence, we were unaware of any case reports in which administration of trimethoprim-sulfamethoxazole in standard doses (160 mg of trimethoprim and 800 mg of sulfamethoxazole given twice daily) has been implicated as a cause of hyperkalemia. In fact, of the 649 patients who received trimethoprim-sulfamethoxazole in standard doses and who were monitored within a hospital setting in the Boston Collaborative Drug Surveillance Program, none developed hyperkalemia [1]. Trimethoprim-sulfamethoxazole inhibits amiloride-sensitive sodium channels in the distal nephron and reduces the transepithelial voltage favoring potassium secretion in a dose-dependent fashion [2, 3]. Standard twice-daily doses of trimethoprim-sulfamethoxazole may not maximally inhibit renal potassium excretion because the achievable urinary drug concentrations may only produce a 50% decrease in the electrical gradient [2, 3]. Other factors such as age-related reductions in renal function or defects in renal potassium handling may be required for standard doses of trimethoprim-sulfamethoxazole to express fully the hyperkalemic effect. Prospective studies are needed to examine this possibility.
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Author and Article Information
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The Brookdale Hospital Medical Center; Brooklyn, NY 11212
1. Lawson DH, Jick H. Adverse reactions to co-trimoxazole in hospitalized medical patients. Am J Med Sci. 1978; 275:53-7.
2. Choi MJ, Fernandez PC, Patnaik A, Coupaye-Gerard B, D'Andrea D, Szerlip H, et al. Trimethoprim-induced hyperkalemia in a patient with AIDS. N Engl J Med. 1993; 328:703-6.
3. Velazquez H, Perazella MA, Wright FS, Ellison DH. Renal mechanism of trimethoprim-induced hyperkalemia. Ann Intern Med. 1993; 119:296-301.
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