Grapefruit-interaction medications in question are all taken orally, have limited bioavailability — that is, only a small percentage of the active drug makes it into the bloodstream under normal circumstances — and all interact in the GI tract with an enzyme called CYP3A4.
Drug package inserts contain this information, the study pointed out, but many people, including physicians, may not be aware of its importance.
If you enjoy eating grapefruit or other citrus and take prescription drugs, it's advisable to ask your pharmacist or doctor if the drug has the potential for a food interaction.
In all, 85 drugs are known to cause a drug interaction when taken with grapefruit, but not all of these medications cause such serious adverse effects.
For some, the way grapefruit interacts with it can actually be beneficial.
A preliminary study published in Clinical Cancer Research shows consuming a glass of grapefruit juice makes the anti-cancer drug, sirolimus, three times more powerful without the side effects that typically accompany a higher dosage.
The FDA approved sirolimus to prevent rejection of a kidney transplant, but it can help some people with cancer.
The challenge for cancer patients is that sirolimus is so easily metabolized in the body that it leaves the bloodstream before it has had time to properly work. At higher doses optimal for producing anti-tumor effects, sirolimus causes significant gastrointestinal problems, most commonly nausea and diarrhea.
Dr. Ezra Cohen, a cancer specialist at the University of Chicago Medicine said in a news release that the researchers wanted to see if grapefruit juice could be “used in a controlled fashion to increase the availability and efficacy of sirolimus."
“This is the first study to use a cancer study to harness food-drug interaction,” the researchers wrote.
None of the 138 patients with incurable cancers in early stage trials had a complete response, but 30 percent of patients’ cancers did not advance. One patient saw his or her tumor shrink, which lasted for three years, the study said.