Introduction:
Urinary health is what cranberry juice is best known for, but cranberries are rich in antioxidants and phytochemicals, substances thought to help promote a healthy immune and cardiovascular system. However, there are some instances in which you should avoid cranberry juice intake.
Cranberry and warfarin:
A study by Greenblatt DJ, et al indicated that a single dose of cranberry juice given to healthy persons does not appear to affect warfarin metabolism. However, cranberry juice is often consumed over several days when purchasing a supermarket size bottle. When consumed in larger amounts by a patient taking warfarin, this may increase PTINR levels when previously in a stable range. (1)
Cranberry juice taken with warfarin was found to be associated with an increased blood thinning effect in a 78-year-old man taking 45 mg per week of warfarin to maintain a therapeutic PTINR prothrombin time international normalized ratio (PTINR)for irregular heartbeat. A week after drinking half a gallon of cranberry-apple juice, the patient had a PTINR of 6.45—signaling the level had become supratherapeutic. Cranberry juice intake was stopped and warfarin at 40 mg per week was taken. After 5 days, the INR returned back to an acceptable range between 2.0-3.0. (2)
A case revealed an additional circumstance in which a 46 year old female on warfarin drank cranberry juice for several days resulting in elevation of prothrombin time on 2 separate occasions with cranberry juice as the only dietary change (3).
Greenblatt reviewed available data on the possibly that intake of cranberry juice might significantly alter the international normalized ratio (INR), used to report the results of blood clotting tests, in patients taking warfarin. The data are from case reports in the United Kingdom and led the UK Committee on Safety of Medicines to issue a warning that patients taking warfarin should avoid cranberry juice or cranberry products. However, Dr. Greenblatt’s examination of each case report found that there was no evidence to suggest that cranberry juice inhibited anticoagulation. Further, a study with cranberry juice and flurbiprofen (which is metabolized by the same enzyme that plays a major role in warfarin metabolism, the hepatic CYP2C9 enzyme) found no effect of cranberry juice on the metabolism of this medication. This study concludes that current evidence does not support a need for concern regarding a warfarin and cranberry interaction. (4)
Assessment and Plan:
- Cranberry contains vitamin C and has antioxidant properties for general health promotion but more than 4 ounces per week should be avoided in patients taking warfarin (brand name Coumadin) to avoid potentially prolonging the PTINR.
References:
1.Greenblatt DJ, von Moltke LL, Perloff ES, Luo Y, Harmatz JS, Zinny MA. Interaction of flurbiprofen with cranberry juice, grape juice, tea, and fluconazole: in vitro and clinical studies. Clin Pharmacol Ther 2006;79(1):125-33. http://www.ncbi.nlm.nih.gov/pubmed/16413247/?dopt=Abstract . http://www.ncbi.nlm.nih.gov/pubmed/16413247/
2.Paeng CH, Sprague M, Jackevicius CA. Interaction between warfarin and cranberry juice. Clin Ther. 2007 Aug;29(8):1730-5. http://www.clinicaltherapeutics.com/article/S0149-2918(07)00253-6/abstract
3.Hamann GL, Campbell JD, George CM. Warfarin-cranberry juice interaction.Ann Pharmacother. 2011 Mar;45(3):e17. doi: 10.1345/aph.1P451. Epub 2011 Mar 1. http://www.ncbi.nlm.nih.gov/pubmed/21364039
4.Greenblatt DJ. Cranberry Juice & warfarin: Is there an interaction? Anticoagulation Forum Newsletter 2006; 10(1):1, 3. http://www.acforum.org/docs/ACForum_Spring-06.pdf