BRECKENRIDGE, COLO. — Warfarin plus cranberry juice can add up to big trouble.
A series of five case reports of a suspected clinically significant drug-food interaction between warfarin (Coumadin) and cranberry juice has prompted the United Kingdom's Committee on Safety of Medicines and the Medicines and Healthcare Products Regulatory Agency to warn patients on the oral anticoagulant to limit consumption of cranberry juice or avoid it altogether, Jacci Bainbridge, Pharm.D., said at a conference on epilepsy syndromes sponsored by the University of Texas at San Antonio.
“The volume of cranberry juice in these cases was glasses per day, not gallons and gallons. It was the sort of quantities patients might use to treat a bladder infection or for a body cleansing,” explained Dr. Bainbridge of the University of Colorado, Denver.
The drug-food interaction was manifested by a rise in the international normalized ratio to levels far outside the therapeutic range, resulting in a markedly increased risk of bleeding.
Indeed, the INR in one patient soared to in excess of 50 within 6 weeks after starting to drink cranberry juice regularly; the patient died of gastrointestinal and pericardial hemorrhage, the only known fatality to date.
A cranberry juice/warfarin interaction is biologically plausible. Warfarin is metabolized chiefly by cytochrome P-450 in the liver, and the antioxidant flavonoids contained in the juice are known to inhibit the enzyme pathway, Dr. Bainbridge noted.