C: Warfarin-cranberry juice interaction

Warfarin’s antithrombotic effect maybe influenced by a variety of fac-tors, such as drug, food, herbal product, and disease state interactions, as well as patient adherence.1,2 There have been several case reports of cranberry juice or cranberry sauce potentiating the effects of warfarin by elevating the INR.3-8 Cranberry juice is a commonly con-sumed beverage that may also be used by patients for self-treatment in the pre-vention or adjunctive treatment of uri-nary tract infections.9 We report a case that describes repeat-ed international normalized ratio (INR) elevations of 4.6 and 6.5 in a patient pre-viously stable on warfarin after ingestion of 1420-1893 mL of cranberry juice cocktail daily for several days. The re-currence of the INR elevation on 2 sepa-rate occasions distinguishes our case from other published reports. Case Report A 46-year-old African American wom-an weighing 86 kg had been receiving a total weekly warfarin dose of 56 mg after a mitral valve replacement in 2004. Her medical history included stage 1 sar-coidosis, uterine fibroids, anemia, cardiomyopathy, and de-pression. These disease entities were stable throughout the reporting period. There were also no medication changes throughout the reporting period. The patient did not use herbal medications, alcohol, or topical methylsalicylate. She reported using acetaminophen rarely. This patient was treated in an anticoagulation clinic where patients are scheduled to be seen at 4-week intervals when their INRs are therapeutic and 1- to 2-week intervals when their war-farin doses are changed. During the 4 months prior to the incident INR, the patient’s average INR was 2.0, with a range of 1.6-2.2, while taking the same weekly dose of warfarin. While her therapeutic range was 2.5-3.5, her IN