For years, doctors have warned patients that grapefruit juice can cause overdoses when combined with anything from cholesterol medication to antihistamines. Now, researchers at the University of Chicago medicine have discovered that drinking one glass of grapefruit juice a day can actually reduce the dosage, cost and side effects of certain drugs, including those used to treat cancer.
Doctors were interested in studying the sirolimus, a drug approved to prevent rejection after kidney transplant, on patients with incurable cancer. Knowing that only 14% of the drug is absorbed into the blood stream, and that higher doses can cause nausea and diarrhea, they went about searching for a supplement that would boost sirolimus absorption.
That was when lead researcher Dr. Ezra Cohen remembered grapefruit juice can increase blood levels of certain drugs. “We saw that not as a problem but as an opportunity to enhance the pharmacology to not only sirolimus but to a wide range of drugs.”
Grapefruit juice’s potential pharmaceutical prowess stems from its ability to inhibit enzymes in the intestine that break down certain drugs. The effect begins within a few hours of drinking it and wears off gradually over a few days.
So Cohen and his team gave some patients grapefruit juice to see if they could get more sirolimus into their bloodstreams. At first, Cohen gave his patients grapefruit juice, but nothing happened. That was when the Florida Department of Citrus got wind of the study and offered to test a sample of the grapefruit juice Cohen’s team was using.
“Dr. Cohen didn’t realize that the compound that enhances drug absorption can be degraded kind of drastically,” said Dan King PhD, the director of scientific research at the department. “This juice he was using didn’t have a whole lot of this compound present.”
The compound is furanocoumarin, and it works by inhibiting enzymes in the intestine that would otherwise limit drug absorption. Cohen’s juice had almost none because it was canned and stored in the non-refrigerated section of the grocery store. Such juice is heated to temperatures that degrade the furanocoumarin.
Having identified the problem, the Department of Citrus supplied “potent” grapefruit juice for the rest of the study. It worked, increasing sirolimus levels by an incredible 350% and lowering the necessary doses from 90 mg per week to between 25 and 35 mg per week.
“Sure enough, what they sent was very potent,” Cohen said. “It allowed us to reduce the dose of sirolimus dramatically.” It could also reduce the cost of cancer treatments which are problematic for a lot of patients.
Unfortunately, the study didn’t show that the sirolimus-grapefruit combo was completely effective against cancer. None of the 138 patients in the study had a complete response, but about 30% achieved stable disease, meaning a period when their cancers did not advance. And one patient in the grapefruit juice group experienced significant tumor shrinkage that lasted for more than three years.
Jerry Avorn MD, chief of the Division of Pharmacoepidemiology and Pharmacoeconomics at Brigham and Women’s Hospital in Boston, did not work with researchers on the study, but said he is excited about the results. “It’s important not to see this as a new cure for cancer, but rather, it’s a very interesting way of using a known food-drug interaction as a means of getting better drug levels into cancer patients.”
SRxA’s Word on Health believes this is the first cancer study to harness a grapefruit-drug interaction rather than warn against it. We look forward to more.