TUESDAY, May 9, 2006 (HealthDay News) -- Researchers say they've identified the substances in grapefruit juice that can produce unwanted side effects when the juice is taken with certain drugs.
The discovery may make it possible to offer grapefruit juice that is free of these substances, called furanocoumarins, or add them to drugs to boost their effect, the researchers say.
People are routinely told by their doctors to avoid drinking grapefruit juice while taking a variety of medications because of potentially dangerous side effects. For instance, the beverage should be avoided when taking certain blood-pressure or cholesterol-lowering drugs, as well as HIV medications, organ-transplant drugs and sedatives.
The reason: Grapefruit juice can cause these drugs to enter the blood stream more efficiently, thereby increasing the dose and effect -- and the potential for undesirable and even dangerous side effects.
It had been thought that the flavonoids that give grapefruit juice its bitter taste caused the drug interaction, said study lead researcher Dr. Paul Watkins, director of the General Clinical Research Center at the University of North Carolina at Chapel Hill.
"What this study shows is that if you leave all that stuff in and take out a group of substances called furanocoumarins, you get rid of this property of the juice," Watkins said.
The study findings appear in the May issue of the American Journal of Clinical Nutrition.
In their study, Watkins and his colleagues compared orange juice, whole grapefruit juice and grapefruit juice that had the furanocoumarins removed. "We found that once you took the furanocoumarins out, the juice behaved like orange juice," he said. "That's certainly pretty convincing evidence that these are the active ingredients in the juice."
According to Watkins, there are three implications to the finding.
First, since the substances that cause drug interactions have been found, researchers can look at a number of other fruits to see if they contain furanocoumarins and predict whether they will cause the same problem.
Second, manufacturers of grapefruit juice could offer a version of the juice that has the furanocoumarins removed, eliminating the potential for drug interaction, Watkins said. "If there were a market, it would be possible to offer furanocoumarin-free grapefruit juice for people taking certain drugs, just as there is lactose-free milk," he said. "It doesn't affect the taste very much."
Third, furanocoumarins could be added to certain drugs to improve their "bioavailability," or ability to enter the blood stream, Watkins said. "The effect of grapefruit juice is to boost entry of these drugs into the body, and that can be a good thing if you can control it," he said. "It turns out that you don't just get more, you get a more reliable delivery -- there is less variation from one person to another when you do this," he said.
One expert thinks that adding furanocoumarins to medications might be the most important potential development to come out of this study.
"The ability to produce grapefruit juice free of the chemicals that interact with drugs is in some ways trivial, as few people would find avoiding grapefruit juice a true hardship," said Dr. David L. Katz, an associate professor of public health and director of the Prevention Research Center at Yale University School of Medicine.
But, the potential to use these chemicals in grapefruit juice to adjust drug levels is of real interest, Katz said. "As unknowns, chemicals in grapefruit juice interacting with drugs were merely a potential hazard. Now that they have been identified, they may be useful therapeutic agents in their own right," he said.
For more on drugs and grapefruit juice, visit Columbia University.