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Fruits Inhibit Absorption of Some Orally Administered Drugs

Aug 20 - Juice from grapefruit, oranges, and apples, as well as the whole fruits, substantially decrease oral absorption of some drugs by blocking an intestinal uptake transporter, according to a report at the 236th National Meeting of the American Chemical Society, underway in Philadelphia.
"In order to get the most consistent effect from drugs, they should be taken with a glass of water on an empty stomach," Dr. David G. Bailey said during his presentation.
Dr. Bailey's group was the first to report that grapefruit juice blocks the drug-metabolizing enzyme cytochrome p450 3A4, boosting blood concentrations of some drugs to potentially toxic levels. Since then, nearly 50 medications have been found to carry the risk of grapefruit-induced adverse drug reactions.
Their current research documented the opposite effect on the antihistamine fexofenadine. When consumed with either a glass of grapefruit juice or water containing the grapefruit flavonoid naringin, drug absorption was reduced by half. As a consequence, the medication's effectiveness may be markedly reduced.
"Naringin appears to have great specificity for certain drugs (and vitamin supplements), those that are water soluble and highly polarized," Dr. Bailey added.
So far, the researchers have observed similar effects on the immunosuppressant cyclosporine, the antineoplastic agent etoposide, some beta blockers (atenolol, celiprolol, talinolol), and some antibiotics (ciprofloxacin, levofloxacin, itraconazole).
"This is probably just the tip of the iceberg," the pharmacologist said.
Unlike the prolonged effect exerted on cytochrome p450, Dr. Bailey, at the University of Western Ontario in London, and his associates observed that grapefruit's effect on the intestinal transport enzyme -- organic anion-transporting polypeptide (OATP)1A2 -- lasts no longer than about 4 hours.
"So there is a window of time where you can enjoy juices without worrying about their drug interactions," Dr. Bailey noted.
However, because flavonoids are widely found in fruits and vegetables, the effect is not likely to be limited to the three fruits they tested.
When asked if juices should have warning labels about potential drug interactions, Dr. Bailey smiled and replied, "This research is still in its infancy. However, it's important for health care providers to be aware and to counsel their patients about which drugs are a concern."

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