Curiouser and Curiouser

The Grapefruit Effect, Demystified

Tuesday, March 27, 2007

Scientists have known for a while that grapefruit exaggerates the effects of certain drugs, sometimes with dangerous results. They just weren't sure why.

Now they have the answer: furanocumarins, chemicals found in only three citrus fruits -- grapefruits, pomelos and Seville oranges. Even very small amounts -- "sub-micro levels" -- can cause potentially hazardous interactions with some medications, according to Paul Watkins, professor of medicine at the University of North Carolina at Chapel Hill, who led the research team. "You can't taste them . . . but they are very powerful," he adds.

Block That Enzyme According to Watkins, furanocumarins "knock down," or inhibit, an enzyme in the intestines called CYP 3A4, which is critical to the proper breakdown of drugs. Without the enzyme, drugs build up in the bloodstream to potentially toxic levels, and side effects increase.

The grapefruit effect appears with some well-known drugs such as Lipitor (atorvastatin) and Zocor (simvastatin), taken for high cholesterol; Plendil (felodipine) and Procardia (nifedipine), for high blood pressure; Cordarone (amiodarone), for an irregular heartbeat; and some anti-HIV medications.

I'll Take Mine With Furanocumarins Ironically, the discovery about harmful interactions -- published last year in the American Journal of Clinical Nutrition but largely overlooked -- may one day lead to more potent drugs.

"Wouldn't it make sense to just mix these [effect-enhancing] compounds right into the pill?" asks Watkins. Adding nontoxic amounts of furanocumarins to pills can actually "boost the absorption of drugs and make the absorption more reliable," he adds.

Scientists and pharmaceutical companies are already working on making this happen, but it could be years before the substance is routinely added to medications.

Another possibility, says Watkins: reformulated citrus drinks. "This could be like 'lactose-free milk.' . . . You could pay a little extra for furanocumarin-free grapefruit juice."

-- Ranit Mishori

© 2007 The Washington Post Company