Grapefruit Juice Boosts Effectiveness of Anti-Cancer Drug

Research has shown that grapefruit juice can significantly slow the metabolism of the drug sirolimus, which has already been approved for transplant patients but may also be useful in the treatment of cancer. Ezra Cohen, MD, a cancer specialist at the University of Chicago Medicine, and colleagues conducted three simultaneous phase-1 trials of sirolimus in which patients received only sirolimus, sirolimus plus ketoconazole, or sirolimus plus grapefruit juice. In total, 138 patients with incurable cancer and no known effective therapy took part in the studies. Results showed that the optimal cancer-fighting dose for those taking sirolimus was about 90 mg per week, but at doses above 45 mg, the drug caused serious gastrointestinal side effects, such as nausea and diarrhea. However, in study participants who drank eight ounces a day of grapefruit juice sirolimus levels increased by 350%, thus reducing the needed dosage to between 25 and 35 mg of sirolimus per week. The drug ketoconazole increased sirolimus levels by 500%, thereby reducing the dosage of sirolimus to just 16 mg per week. The authors note that although ketoconazole was slightly more effective at boosting sirolimus levels, grapefruit juice has the advantage that it is non-toxic and does not cause any unpleasant side effects. The authors concluded: “We have at our disposal an agent that can markedly increase bioavailability and, critically in the current environment, decrease prescription drug spending on many agents metabolized by P450 enzymes.”