For almost a decade, people have been told by their doctors and pharmacists to avoid grapefruit juice if they are being treated with certain medications, including some drugs that control blood pressure or lower cholesterol. Studies have shown that grapefruit juice can cause more of these drugs to enter the blood stream, resulting in undesirable and even dangerous side effects.

The drugs affected by grapefruit juice usually have some difficulty entering the body after they are consumed because an intestinal enzyme, CYP3A, partially destroys them as they are absorbed. Grapefruit juice, but not other commonly consumed fruit juices, inhibits this enzyme, allowing more of these drugs to enter the body.

It was originally assumed that the ingredients responsible for drug interactions were the flavonoids that give grapefruit juice its bitter taste.

The new study shows that a group of chemicals called furanocoumarins are the likely culprit.

"This is the best evidence to date that furanocoumarins are the active ingredients in grapefruit juice that cause the interaction with medications," said Dr. Paul Watkins, the Dr. Verne S. Caviness distinguished professor of medicine and director of UNC's General Clinical Research Center (GCRC). Watkins led the study team.

A report of the new findings appears in the May issue of the American Journal of Clinical Nutrition.

To determine whether furanocoumarins are responsible for grapefruit juice-drug interactions, Watkins worked with scientists at the Florida Department of Citrus to selectively remove only the furanocoumarins from the juice. He and his collaborators then studied the effect of the whole juice versus furanocoumarin-free juice on the ability to affect absorp
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Contact: Leslie H. Lang
llang@med.unc.edu
919-843-9687
University of North Carolina School of Medicine
9-May-2006