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May 9 (foodconsumer.org) - Scientists have identified a grapefruit juice compound, which is likely to be responsible for the dangerous interaction between grapefruit juice and certain drugs, according to a study published in the May issue of the American Journal of Clinical Nutrition.

Grapefruit juice has been known for decades to have potentially dangerous interactions with certain drugs including some drugs that control blood pressure or lower cholesterol. It has previously been believed that the possible culprits are flavonoids.

But the new study, conducted by Dr. Paul Watkins, the Dr. Verne S. Caviness distinguished professor of medicine and director of UNC's General Clinical Research Center (GCRC) at University of North Carolina School of Medicine and colleagues, have found that the actual culprit are furanocoumarins.

"This is the best evidence to date that furanocoumarins are the active ingredients in grapefruit juice that cause the interaction with medications," said Dr. Watkins.

In their study, Dr. Watkins and colleagues recruited 18 healthy volunteers who took 10 milligrams of felodipine, an anti-hypertension drug known to interact with grapefruit juice. Then, they assigned the participants either orange juice, regular grapefruit juice or grapefruit juice with furanocoumarins removed.

Blood test results indicated that "in contrast to whole grapefruit juice, the furanocoumarin-free grapefruit juice behaved like orange juice and did not cause an interaction with felodipine."

Early studies have found the drugs affected by grapefruit juice usually have some difficulty entering the body after they are consumed because an intestinal enzyme, known as CYP3A, partially destroys them as they are absorbed. Grapefruit juice inhibits this enzyme, allowing more of these drugs to enter the body and causing dangerously high levels of drugs in the bloodstream.

"First, it should now be possible to market the furanocoumarin-free grapefruit juice to patients who would otherwise need to avoid grapefruit. In addition, it should be possible to screen new foods for the potential for drug interactions by determining whether they contain furanocoumarins," said Dr. Watkins.

"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."

However, it remains unknown whether furanocoumarins are also responsible for the interactions of grapefruit juice with other drugs.

A detailed list of drugs that can potentially interact with grapefruit juice can be found in a paper published in the December 2004 issue of the American Journal of Nursing.

For more information, visit drug interaction center

Researchers Discover Why Grapefruit Juice Interacts With Drugs

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