Researchers from the University of Sydney in Australia investigated the possible impact of two commonly used herbal medicines, garlic and cranberry, on the anticoagulant, warfarin (Coumadin).
First, the details.
12 healthy men of known CYP2C9 and VKORC1 genotype were randomly assigned to each treatment.
1 dose of warfarin 25 mg administered alone
1 dose of warfarin 25 mg administered after 2 weeks of pretreatment with either garlic or cranberry.
CYP2C9 and VKORC1 are genetic variants that affect warfarin metabolism.
And, the results.
Cranberry significantly increased the area under the INR-time curve by 30% when taken with warfarin compared to warfarin alone.
INR (International normalized ratio) is a measure of the ability of blood to clot where increased values reflect less clotting
Garlic had no effect on warfarin.
The bottom line?
The authors concluded, “Cranberry alters the pharmacodynamics of warfarin with the potential to increase its effects significantly. Co-administration of warfarin and cranberry requires careful monitoring.”
Both herbal medicines showed some evidence of VKORC1 genotype-dependent interactions with warfarin, which the authors think is worthy of further investigation.
This study supports earlier reports in individual patients.
John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at www.Vicus.com, a complementary and alternative medicine website.