To the Editor.—The article by Dr Hylek and colleagues1 was an important contribution about the drug interactions of warfarin with acetaminophen and other agents. The authors mention dietary sources of vitamin K as a meaningful antagonist to warfarin resulting in a lower prothrombin time or INR. But they apparently did not ask the patients about consumption of dietary supplements, such as vitamins and multivitamin combinations. Several studies suggest that about 50% of the adult white population take a dietary supplement.2,3 Vitamin K can be purchased in health food stores and is present in some multivitamins.
Eliason BC, Larson W. Acetaminophen and Risk Factors for Excess Anticoagulation With Warfarin. JAMA. 1998;280(8):695-697. doi:10-1001/pubs.JAMA-ISSN-0098-7484-280-8-jbk0826