U.S. researchers have identified the compound in grapefruit juice that affects how some drugs are absorbed in the body, according to their study reported in the American Journal of Clinical Nutrition. They said Tuesday grapefruit juice might be used to help lower medication dosages.
Grapefruit juice is known for its effects on drug metabolism, both positive and negative.
The reason is the intestinal enzyme CYP3A, which partially destroys drugs as they are absorbed. Grapefruit juice, like no other fruit juice, interferes with CYP3A, so the body ends up absorbing more of the drug.
Dr. Paul Watkins of the University of North Carolina at Chapel Hill and colleagues say they have identified the substance in grapefruit juice that is responsible — furanocoumarin.
“It should now be possible to market the furanocoumarin-free grapefruit juice to patients who would otherwise need to avoid grapefruit,” Watkins said in a statement.
“In addition, it should be possible to screen new foods for the potential for drug interactions by determining whether they contain furanocoumarins,” Watkins said.
“Finally, it may be possible to add furanocoumarins to formulations of certain drugs that tend to be poorly or erratically absorbed to improve their oral delivery.”
To test the theory that furanocoumarin was the responsible compound,
Watkins and colleagues filtered it out of grapefruit juice, which they discovered was then less bitter but otherwise unaltered.
Then they tested 18 men and women taking various drugs on a regular basis including aspirin and birth control pills.
Each fasted in the hospital and got a single dose of the blood pressure drug felopidine, sold under the brand name Plendil, along with either normal grapefruit juice, furanocoumarin-free juice or orange juice.
They then ate and drank normally and blood samples were taken throughout day.
In each volunteer, the normal grapefruit juice made between 6 percent to 230 percent more Plendil available in the blood, the researchers reported. The furanocoumarin-free grapefruit juice and orange juice had no such effect.