Grapefruit juice can be a boon instead of a bane when taking the cancer drug rapamycin, according to a University of Chicago Medical Center study. Pharmacists have for years warned against washing down medicine with grapefruit juice because it can block enzymatic action in the body, thereby making some drugs dangerously more potent. In the right circumstances, however, grapefruit juice not only makes certain medications more effective but less expensive to take as well.
“Grapefruit juice can increase blood levels of certain drugs three to five times,” study director and cancer specialist Ezra Cohen, MD, said in a UCMC news release. “This has always been considered a hazard. We wanted to see if, and how much, it could amplify the availability, and perhaps the efficacy of rapamycin, a drug with promise for cancer treatment.”
Rapamycin, also known as sirolimus, fights cancer by preventing tumors from sprouting new blood vessels, thereby keeping them in check. However, an enzyme in the intestine breaks down all but about 15 percent of the drug when taken by mouth. This is where grapefruit juice comes to the rescue—it retards the breakdown of rapamycin so it can reach higher levels in the bloodstream, up to four times the level reached without the juice boost.
“That means more of the drug hits the target, so we need less of the drug,” Cohen said.
Since many new oral cancer drugs like rapamycin cost $1,000 or more a month, grapefruit juice can make expensive treatment cheaper. “A daily glass of juice could lower the cost by 50 percent,” Cohen said, noting that during the study, researchers used fresh juice and not the “grocery-store” variety, since key chemicals in the juice have a short shelf life.
One woman in the trial was able to reduce the number of days in the week she had to take rapamycin to just one day. More importantly, she was able not merely to reduce the cost of her treatment, but also to reduce to only one day the length of time she had to endure the fatigue associated with the drug.
GRAPEFRUIT INTERACTIONS FACT: Interactions can occur up to three days after eating or drinking grapefruit, so the common strategy of consuming grapefruit in the morning and taking medicine later in the day does not avoid interactions. Check with your physician for possible interactions with your medications, especially if you are taking drugs for high cholesterol, high blood pressure, or heart arrhythmia.
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