Search Here

A glass a day of grapefruit juice could lower the dosage of caner drugs by up to three times. The combination could help patients avoid side effects associated with high doses of the drug and reduce the cost of the medication.

The study was published in the journal Clinical Cancer Research medication and is the first cancer study to harness this drug-food interaction and

A team of researchers from the University of Chicago set out to examine the effects that foods can have on the uptake and elimination of drugs used for cancer treatment. 

Researchers said the results show that eight ounces a day of grapefruit juice can slow the body's metabolism of a drug called sirolimus, which has been approved for transplant patients but may also help many people with cancer. 

Patients who drank eight ounces a day of grapefruit juice increased their sirolimus levels by 350 percent. A drug called ketoconazole that also slows drug metabolism increased sirolimus levels by 500 percent.

Study Director Ezra Cohen said grapefruit juice, and drugs with a similar mechanism, can significantly increase blood levels of many drugs, but there must be caution.

This has long been considered an overdose hazard," Cohen said. "Instead, we wanted to see if grapefruit juice can be used in a controlled fashion to increase the availability and efficacy of sirolimus."

Grapefruit juice can inhibit enzymes in the intestine that break down sirolimus and several other drugs. The effect begins within a few hours of what the researchers refer to as "grapefruit juice administration." It wears off gradually over a few days.

Researchers used 138 patients with incurable cancer and no known effective therapy for the study. They were given only sirolimus, sirolimus plus ketoconazole, or sirolimus plus grapefruit juice. A frozen concentrate of the juice was used instead of canned juice which researchers said lacked the active ingredients. 

The optimal cancer-fighting dose for those taking sirolimus was about 90 mg per week. At doses above 45 mg, however, the drug caused serious gastrointestinal problems, such as nausea and diarrhea, so patients taking sirolimus alone switched to 45 mg twice a week.

The optimal doses for the other two groups were much lower. Patients taking sirolimus plus ketoconazole, needed only 16 mg per week to maintain the same levels of drug in the blood. Those taking sirolimus plus grapefruit juice, needed between 25 and 35 mg of sirolimus per week.

About 30 percent of patients in the three trials had stable disease, meaning a period when their cancers did not advance. One patient receiving grapefruit juice had a partial response-significant tumor shrinkage-that lasted for more than three years.

Researchers did note that because different people produce varied amounts of the enzymes that break down sirolimus, the effect of grapefruit juice can vary, but tests of enzyme levels may be able to predict how an individual patient will respond.

"The variation in potency of the grapefruit juice itself may be far greater than the variation in the enzymes that break down sirolimus," Cohen said.