A frequent cause of acquired warfarin resistance is drug interaction; however, ingestion of large amounts of vitamin K in food may also be an etiologic factor. A 31-year-old woman on a weight-reducing diet showed evidence of resistance to warfarin sodium therapy. On a regimen of 35 mg of oral warfarin sodium daily, prothrombin time was 14s (control, 12 s). Pharmacokinetic studies did not reveal any evidence of impaired absorption or increased catabolism of the drug. The half-life of her oral warfarin was 26 hours (normal, 15 to 56 hours). Although end-organ resistance was not studied fully, a change of her vegetable-rich, weight-reducing diet (vitamin K content, 1,277 μg) to a regular diet (vitamin K content, 360 μg) resulted in substantial reduction in her warfarin resistance. We conclude that in patients on vegetable-rich, weight-reducing diets, a relative resistance to warfarin may be secondary to their increased dietary intake of vitamin K.
(Arch Intern Med 1981;141:507-509)
Qureshi GD, Reinders TP, Swint JJ, Slate MB. Acquired Warfarin Resistance and Weight-Reducing Diet. Arch Intern Med. 1981;141(4):507-510. doi:10.1001/archinte.1981.00340040103025