Grapefruit Juice Lowers Cancer Drug Dosage

Cancer medication sirolimus dosing lowered with grapefruit juice

(RxWiki News) Did you know that grapefruit juice can impact the way a medication works in your body? It actually increases the amount of the active ingredient available for the body to use in some medications. A new study shows this phenomenon could be very helpful for people taking an anticancer drug.

Advanced cancer patients who drank a glass of grapefruit juice everyday needed only a fraction of the standard dosing of an anticancer drug called Rapamune (sirolimus). 

This finding could substantially decrease toxic side effects and lower cost of the medication.

"Ask your pharmacist if you have any medication questions."

University of Chicago Medicine researchers uncovered this. "Grapefruit juice, and drugs with a similar mechanism, can significantly increase blood levels of many drugs," said study director Ezra Cohen, MD, a cancer specialist at the University of Chicago Medicine, “but this has long been considered an overdose hazard. Instead, we wanted to see if grapefruit juice can be used in a controlled fashion to increase the availability and efficacy of sirolimus."

Eight ounces of grapefruit juice a day increased sirolimus levels by 350 percent. Another drug called ketoconazole, which is used to treat fungal infections, increased sirolimus levels by 500 percent.

Sirolimus is approved by the U.S. Food and Drug Administration to help avoid transplant rejection. It may also offer anticancer benefits.

For the study, Dr. Cohen and his colleagues conducted three simultaneous phase 1 trials. A total of 138 patients with incurable cancer received only sirolimus, sirolimus plus ketoconazole or sirolimus plus grapefruit juice.

The dosages were slowly increased to determine the optimal anticancer dose. For tolerable side effects, that dosage for sirolimus alone was 45 mg twice a week.

Patients taking sirolimus plus ketoconazole needed only 16 mg a week. Those taking the drug with grapefruit juice needed between 25-35 mg a week.

The difference in price of the drug was substantial. At 90 mg a week, the drug would cost about $750 for a 30-day supply, while those drinking grapefruit juice daily would only pay just under $400.

While no patient had a complete response, about 30 percent saw their disease stabilize for a period of time.

While the ketoconazole (brand names - Nizoral, Extina, Xolegel, Kuric) had a slightly stronger response, grapefruit juice has the advantage of not being toxic.

The authors wrote, "Therefore, we have at our disposal an agent that can markedly increase bioavailability (in this study by approximately 350%) and, critically in the current environment, decrease prescription drug spending on many agents metabolized by P450 enzymes.”

The study was published in August in Clinical Cancer Research and supported by the National Institutes of Health.

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Review Date: 
August 7, 2012