SUBJECT: Case reports suggest an association between cranberry juice and potentiation of warfarin. Studies using 240 ml of cranberry juice daily demonstrated no interaction. It is unknown if higher amounts of cranberry juice will interact with warfarin.

WHAT THIS STUDY ADDS: Cranberry juice at 240 ml twice daily does not alter the pharmacodynamics of warfarin.

AIM: To determine if high-dose cranberry juice (240 ml twice daily) alters the pharmacodynamic action of warfarin.

METHODS: Ten male patients taking stable doses of warfarin were given cranberry juice at 240 ml twice daily for 7 days. Prothrombin times were drawn at baseline and days 2, 6 and 8 after administration of the juice. Prothrombin times were averaged for each day and mean times were compared from each study day to baseline using repeated measures ANOVA.

RESULTS: There was no statistical difference between mean prothrombin time at baseline and any day tested during juice administration.

CONCLUSIONS: Cranberry juice (240 ml twice daily for 1 week) did not alter the pharmacodynamics of warfarin in patients.