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Issue 174 Item 11 Patients on Warfarin Advised Against Drinking Cranberry Juice

Jun 22, 2004

Patients taking warfarin should limit or avoid drinking cranberry juice because of the risk of hemorrhage.

British drug safety experts on the Committee on Safety of Medicines said it had received five reports, including one where the patient died, suggesting the juice and drug interact, increasing the potency of the drug.

"Until this possible interaction between cranberry juice and warfarin has been investigated further, it would be prudent for patients taking warfarin to be advised to limit or avoid drinking cranberry juice," the committee said.

The fatal case involved a man whose international normalized ratio (INR) dramatically increased to more than 50 six weeks after he started to drink cranberry juice, it reported in its newsletter "Current Problems in Pharmacovigilance."
The man died from gastrointestinal and pericardial hemorrhage.

In two other cases, less dramatic INR increases were noted while patients were taking cranberry juice. "In one of these the patient was stabilised on a lower dose of warfarin and in the other the INR returned to the therapeutic range after stopping cranberry juice," the report said.

According to the committee, the interaction is biologically plausible since cranberry juice contains antioxidants that inhibit cytochrome P450 activity, and warfarin is mainly metabolized by the P450 isoform CYP2C9.
Cranberry juice has boomed in popularity in recent years and is often used by women to prevent cystitis.


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