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The absence of an interaction between warfarin and cranberry juice: a randomized, double-blind trial.

Ansell J, McDonough M, Zhao Y, Harmatz JS, Greenblatt DJ.
J Clin Pharmacol 49(7):824-30

The question of potentiation of warfarin anticoagulation by cranberry juice (CJ) is a topic of biomedical importance. Anecdotal reports of CJ-warfarin interaction are largely unconfirmed in controlled studies. Thirty patients on stable warfarin anticoagulation (international normalized ratio [INR], 1.7-3.3) were randomized to receive 240 mL of CJ or 240 mL of placebo beverage, matched for color and taste, once daily for 2 weeks. The INR values and plasma levels of R- and S-warfarin were measured during the 2-week period and a 1-week follow-up period. The CJ and placebo groups (n=14 and 16, respectively) did not differ significantly in mean plasma R- and S-warfarin concentrations. Eight patients (4 on CJ, 4 on placebo) developed minimally elevated INR (range, 3.38-4.52) during the treatment period. Mean INR differed significantly (P<.02 only="" on="" treatment="" day="" at="" all="" other="" time="" points="" the="" groups="" did="" not="" differ.="" cranberry="" juice="" has="" no="" effect="" plasma="" s-="" or="" r-warfarin="" levels="" excluding="" a="" pharmacokinetic="" interaction.="" small="" though="" statistically="" significant="" pharmacodynamic="" enhancement="" of="" inr="" by="" cj="" single="" point="" is="" unlikely="" to="" be="" clinically="" important="" and="" may="" random="" change.="" enhanced="" warfarin="" anticoagulation="" attributed="" in="" anecdotal="" reports="" represent="" chance="" temporal="" association.="">