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LETTERS: Robin A Howe Don’t include trimethoprim BMJ 2008; 336: 787 [Full text]

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trimethoprim-induced hyperkalaemia is another reason for making trimethoprim subject to prescription

oscar,m jolobe   (11 April 2008)

trimethoprim-induced hyperkalaemia is another reason for making trimethoprim subject to prescription 11 April 2008
oscar,m jolobe, retired geriatrician manchester medical society, c/o john rylands university library, oxford road, manchester M13 9PP Send response to journal: Re: trimethoprim-induced hyperkalaemia is another reason for making trimethoprim subject to prescription	Over and above the reasons for inclusion of trimethoprim in the prescription only category(1), I would add the risk of hyperkalaemia when standard doses of trimethoprim are administered to elderly patients with impaired renal function(2), especially when this co-exists with diabetes- related hyporeninemic hypoaldosteronism(3). In some of these elderly patients, the risk of hyperkaleamia may be increased by coprescription of angiotensin converting enzyme inhibitors(2). Co-prescription of sulfamethoxazole does not, however, appear to contribute to the risk, and it is recognised that trimethoprim is the culprit drug causing hyperkalaemia even in this context(4). Trimethoprim-related hyperkalaemia is attributable to the inhibition of amiloride-sensitive channels in the distal nephron with resulting impairment of kaliuresis(5). References (1) Howe R Don't include trimethoprim British Medical Journal 2008:336:787 (2)Marinella MA Trimethoprim-induced hyperkalemia: An analysis of reported cases Gerontology 1999:45:209-12 (3) Margassery S., Bastani B Life-threatening hyperkalemia and acidosis secondary to trimethoprim- sulfamethoxazole treatment Journal of Nephrology 2001:14:410-14 (4) Perazella MA Trimethoprim-induced hyperkalemia Drug Safety 2000:22:227-36 (5) Schlanger LE., Kleyman TR., Ling B K+ sparing diuretic actions of trimethoprim: inhibition of Na+ channels in A6 distal nephron cells Kidney International 1994:45:1070-6 Competing interests: None declared