Grapefruit juice and the response to warfarin

Area of Science:

• Pharmacology
• Nutrition Science
• Clinical Pharmacy

Background:

• Warfarin is a common anticoagulant medication requiring careful monitoring.
• Grapefruit juice is known to interact with various medications, potentially altering their efficacy.
• The impact of frozen grapefruit juice on warfarin therapy has not been extensively studied.

Purpose of the Study:

• To investigate the effect of prepared frozen grapefruit juice on prothrombin times (PTs) and International Normalized Ratios (INRs) in patients on stabilized warfarin therapy.
• To determine if grapefruit juice consumption alters anticoagulation levels in patients undergoing warfarin treatment.

Main Methods:

• A prospective study involving patients on stabilized warfarin therapy (target INR 2-3).
• Participants consumed 8 oz of prepared frozen grapefruit juice three times daily for one week.
• Prothrombin times (PTs) and INRs were measured at baseline and on days 2, 6, and 8.

Main Results:

• Nine male subjects (mean age 66 years) completed the study; one withdrew due to diarrhea.
• Reported compliance with juice consumption ranged from 85.7% to 100%.
• No significant differences were observed in PT or INR values throughout the study period.

Conclusions:

• Ingestion of grapefruit juice prepared from frozen concentrate does not alter prothrombin times in patients treated with warfarin.
• Frozen grapefruit juice appears to be safe for patients on stabilized warfarin therapy concerning anticoagulation levels.