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Editor's Correspondence |

Apparent Warfarin Potency Inconsistencies Compromise Effectiveness

Bruce M. Rothschild, MD
Arch Intern Med. 2003;163(10):1243. doi:10.1001/archinte.163.10.1243-a.
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An alternative message can perhaps be derived from the article by Meyer et al.1 The article documents that INR was outside therapeutic range in 59% of patients receiving warfarin. The inference is that appropriate levels of anticoagulation control were not achieved in almost half. Is this acceptable? Is there a problem with the paradigm or is medication potency undependable?

Such a problem was uncovered several years ago when inconsistency in warfarin sodium (Coumadin; DuPont Pharma, Wilmington, Del) potency was discovered.2 At that time, the problem was attributed to excess heat exposure during postal transport of the mail order prescription. Subsequently, we have had reason to suspect a larger problem. Wide weekly variation in individual patient dosage response made anticoagulation control challenging.3 A search for confounding factors was unsuccessful. Only the Dupont trade name product had been provided. There had been no alteration in concomitant medication or health product ingestion or dietary habits (eg, variable ingestion of vitamin K–containing foods).

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