Dennis Mungall, PharmD; Richard White, MD
To the Editors: Gurwitz and coworkers (1) purport to show that the anticoagulant response to warfarin increases with age due to an "increased sensitivity" to warfarin; however, the ratio of warfarin dose to prothrombin time response used by the authors as the principal measure of sensitivity does not allow the differentiation of pharmacokinetic variability from pharmacologic sensitivity. In a prospective study of 88 chronically treated outpatients, we showed that age does not alter the pharmacodynamic response to warfarin (2).
The study by Shepard and coworkers (3), cited in dismissing a change in warfarin pharmacokinetics with age, was limited by a
Mungall D, White R. Aging and Warfarin Therapy. Ann Intern Med. ;117:878–879. doi: 10.7326/0003-4819-117-10-878
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Published: Ann Intern Med. 1992;117(10):878-879.
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