Twenty years ago, Dr David Bailey, of the University of Western Ontario discovered that grapefruit juice can dramatically increase the body's absorption of high-blood-pressure drugs, potentially causing dangerous effects from excessive drug concentrations in the blood. Since then, other researchers have identified other medications that interact with grapefruit juice and, as a result, some prescription medications now carry warning labels against drinking or eating grapefruit while taking the drugs.

Dr Bailey and team have now studied healthy volunteers who were asked to take the antihistamine fexofenadine while drinking grapefruit juice, water containing naringin – the substance in grapefruit juice that gives it a bitter taste – or water alone. They found that participants who drank grapefruit juice or water with naringin absorbed only half the amount of the antihistamine as that absorbed by the participants who only drank water. They also found that naringin appears to block a key drug uptake transporter, called OATP1A2, which is involved in transporting the drugs from the small intestine into the bloodstream.

It is possible that grapefruit juice may not be the only type of fruit juice that affects drug absorption, as orange and apple juices also contain naringin-like substances.

Dr Bailey reported his findings at the National Meeting of the American Chemical Society in Philadelphia.

First published in October 2008

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