MONDAY, April 20, 2009 (HealthDay News) -- Grapefruit juice boosts the anti-cancer effects of the drug rapamycin, according to a small study that included 25 patients with advanced solid tumors, for which there is no effective treatment.
The patients took 15- to 35-milligram doses of the drug, as a liquid, once a week. After the first week of the study, they also drank a glass (eight ounces) of grapefruit juice immediately after taking the drug and once a day for the rest of the week.
On this regimen, 7 (28 percent) of the patients had stable disease, with little or no tumor growth. One patient who had a partial response, with tumor shrinkage of about 30 percent, was still doing well more than a year after starting the study.
More than half of the patients experienced side effects such as elevated blood sugar levels, diarrhea, low white blood cell counts, and fatigue.
The findings were to be presented Monday at the annual meeting of the American Association for Cancer Research, in Denver.
For many years, doctors and pharmacists have warned patients that grapefruit juice can interfere with enzymes in the body that break down and eliminate certain kinds of drugs.
"Grapefruit juice can increase blood levels of certain drugs three to five times. 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," stud director Dr. Ezra Cohen, a cancer specialist at the University of Chicago Medical Center, said in a center news release.
Rapamycin, also called sirolimus, was originally developed to suppress the immune system and prevent rejection in kidney transplant patients. It's being studied as a cancer drug, because it disrupts a biochemical pathway involved in the growth of new blood vessels needed by tumors to grow. However, less than 15 percent of rapamycin is absorbed by the body when the drug is taken by mouth.
Grapefruit juice contains compounds called furanocoumarins that decrease the breakdown of rapamycin and increase blood levels of the drug three- to fourfold, which means more of the drug can reach its cancer target, according to the researchers.
The U.S. Food and Drug Administration has more about drug interactions.