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Cause of Grapefruit Juice Drug Interaction Identified

Furanocoumarins inhibit action of intestinal enzyme

WEDNESDAY, May 10 (HealthDay News) -- The active ingredients in grapefruit juice that cause potentially dangerous interactions with some drugs are furanocoumarins, not, as previously suspected, the flavonoids that give the drink its bitter taste, according to a study published in the May issue of the American Journal of Clinical Nutrition.

Paul B. Watkins, M.D., of the University of North Carolina in Chapel Hill, and colleagues removed furanocoumarins from grapefruit juice while all other major ingredients such as flavonoids were retained. They conducted a three-way randomized crossover study with 18 healthy volunteers who ingested 10 mg of felodipine with the treated grapefruit juice, untreated grapefruit juice and orange juice at least one week apart. Blood samples were collected over a 24-hour period.

The maximum concentration of felodipine in plasma was greater after consumption of untreated grapefruit juice compared with the furanocoumarin-free grapefruit juice or the orange juice. There was no significant difference between orange juice and furanocoumarin-free grapefruit juice in terms of median time to maximum plasma concentration or terminal half-life.

"It should now be possible to market the furanocoumarin-free grapefruit juice to patients who would otherwise need to avoid grapefruit," Watkins notes in a statement. "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," he adds.

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