GRAPEFRUIT JUICE AND THE RESPONSE TO WARFARIN

The effect if any of prepared frozen grapefruit juice on prothrombin t imes (PTs) in patients undergoing stabilized warfarin therapy was stud ied. Patients receiving low-intensity warfarin therapy (targeted Inter national Normalized Ratio [INR], 2-3) who had two consecutive baseline PTs within 10% of each other were recruited. Patients who regularly c onsumed grapefruit juice or alcohol or who were taking drugs known to interact with grapefruit juice were excluded. A one-week supply of fre shly prepared frozen grapefruit juice in individual 8-oz containers wa s given to all the subjects, who were told to drink the entire content s of one container three rimes a day for one week. PTs were measured a ad INRs calculated on the day before grapefruit juice ingestion began (day 0) and on days 2, 6, and 8. Ten men (mean age, 66 years) were enr olled; one withdrew because of diarrhea. Compliance in consuming the j uice was reported to range from 85.7% to 100% among patients. There wa s no significant difference among PT or INR values over the course of the study in any of the nine subjects. Ingestion of grapefruit juice p repared from frozen concentrate did not change PTs in patients treated with warfarin.