From the Guidelines
Cranberry consumption is unlikely to significantly affect INR levels in patients taking warfarin, as long as it is consumed in modest amounts, according to a small, randomized, placebo-controlled trial 1. When considering the potential interaction between cranberry and warfarin, it's essential to look at the most recent and highest quality evidence. The study published in Circulation: Arrhythmia and Electrophysiology in 2022 1 found that modest cranberry consumption did not affect INR levels. Some key points to consider:
- Modest cranberry consumption, defined as no more than 24 ounces per day, is unlikely to cause significant changes in INR levels 1.
- Patients on warfarin should maintain consistent cranberry intake to avoid potential fluctuations in anticoagulation control 1.
- Regular INR monitoring is crucial when making any dietary changes, including adding or removing cranberry products from the diet.
- While there are reports of cranberry potentiating warfarin effects, these are often based on case reports or small case series, and the evidence is not strong enough to support a significant interaction 1. It's also important to note that other factors, such as the type of cranberry product consumed and individual patient characteristics, may influence the potential interaction between cranberry and warfarin 1.
From the FDA Drug Label
Bromelains, danshen, dong quai (Angelica sinensis), garlic, Ginkgo biloba, ginseng, and cranberry products are associated most often with an INCREASE in the effects of warfarin sodium tablets. You should also avoid intake of cranberry juice or any other cranberry products. Notify your health care provider if any of these products are part of your normal diet.
Cranberries may affect INR levels. Cranberry products are associated with an increase in the effects of warfarin sodium tablets, which may lead to an increased INR response 2. It is recommended to avoid intake of cranberry juice or any other cranberry products while taking warfarin sodium tablets, and to notify the healthcare provider if these products are part of the normal diet 2.
From the Research
Cranberry Interaction with Warfarin
- The interaction between cranberry juice and warfarin has been reported in several case studies, suggesting that cranberry juice may increase the international normalized ratio (INR) in patients taking warfarin 3, 4, 5.
- A case report published in Clinical Therapeutics in 2007 described a 78-year-old man who experienced an elevated INR after consuming cranberry juice while taking warfarin 3.
- Another case report published in The Annals of Pharmacotherapy in 2011 described a 46-year-old woman who experienced elevated INR values on two separate occasions after consuming cranberry juice cocktail while taking warfarin 4.
- A review of the literature published in The Consultant Pharmacist in 2012 noted that while the majority of pharmacokinetic and pharmacodynamic studies did not find a significant interaction between cranberry and warfarin, several case reports suggest that cranberry products may increase INR values in patients on warfarin 5.
Mechanism of Interaction
- The mechanism of the interaction between cranberry juice and warfarin is not fully understood, but it may involve the inhibition of the hepatic CYP2C9-mediated metabolic clearance of warfarin by components in cranberry 6.
- However, a systematic in vitro-in vivo evaluation published in the Journal of Experimental Pharmacology in 2010 found that a cranberry juice that inhibited warfarin metabolism in human liver microsomes had no effect on warfarin clearance in healthy participants 6.
Clinical Implications
- Practitioners should consider cranberry usage as a potential contributor in the evaluation of supratherapeutic INR values in patients on warfarin 5.
- Patients taking warfarin should be advised to avoid consuming cranberry juice or to monitor their INR values closely if they choose to consume cranberry juice 3, 4, 5.