Grapefruit juice inhibits enzymes in the intestine that normally break down anticancer drugs. Thus, the drug stays in the body longer. This has now been shown in a study by US researchers.
Researchers have studied the interaction of food with a drug for the first time in a cancer study. The result: grapefruit can make cancer drugs more effective. A glass a day increases levels of the drugs in the blood by up to 350 percent – which could lower the dose needed.
Philadelphia. Grapefruit juice can make some cancer drugs more effective. The fruit juice inhibits enzymes in the intestine that normally break down these drugs. This keeps the drug in the body longer and reduces the dose needed to achieve the same effect. This is the result of a study conducted by U.S. researchers with 138 cancer patients, as reported by the scientists in the journal "Clinical Cancer Research" Report.
Researchers had studied the effect of grapefruit juice on the drug sirolimus. This substance, also known as rapamycin, has long been used to dampen the immune system in transplants, but according to the latest findings it is also effective against cancer tumors.
Just a scant quarter of a liter of grapefruit juice increased the level of sirolimus in the blood of these patients by up to 350 percent, the researchers write. To get to the drug's optimal effective blood level, these patients needed only 25 to 35 milligrams of sirolimus per week instead of the 90 milligrams that would otherwise be required.
Food and drug interaction
"This is the first cancer study to examine this interaction of food with a drug", Write study leader Ezra Cohen of the University of Chicago and his colleagues. It shows that a non-toxic food available in any supermarket can significantly improve the bioavailability of some drugs.
Sirolimus is a substance that inhibits the proliferation of cells and can therefore also slow down the growth of tumors. For some cancers, including Kaposi's sarcoma and hepatocellular carcinoma, this has been shown in studies, the researchers explain. Some chemicals related to sirolimus are also already being used to treat kidney cancer. Some tumors of the nervous system used. These drugs are broken down in the body by certain enzymes called p70-S6 kinases. The drugs must therefore be dosed relatively high to compensate for this ongoing degradation.
According to the researchers, the effect of fruit juice now found could help lower the dose of sirolimus and related agents in the future. This would spare patients many harmful side effects. But at the same time, they say, this also makes treatments much less expensive.
Anticancer drugs with and without fruit juice
For their study, the researchers divided 138 patients with terminal cancer into three groups. One received only the tumor-inhibiting sirolimus twice a week. The second group of patients took the drug plus a quart of grapefruit juice, and the third took sirolimus plus ketoconazole, a chemical that also inhibits degradative enzymes.
In all groups, the scientists increased the dosage of the anticancer drug only slowly until it reached the optimally effective concentration in the patients' blood. Patients taking only sirolimus needed 90 milligrams of the drug per week to get to optimally effective blood levels, researchers report. Patients who additionally drank grapefruit juice only needed 25 to 35 milligrams of the drug.
The fruit juice increased the concentration of the carcinogen in their blood by up to 350 percent, Cohen and his colleagues write. In the ketoconazole group, only 16 milligrams of the anticancer drug were needed. This chemical has a somewhat stronger effect than the fruit juice. The advantage of the juice, however, is that it is not toxic and can not cause an overdose.