(Ivanhoe Newswire) -- Washing down your medicine with fruit juice may be a bad idea.

You may have heard that grapefruit juice can increase the absorption of certain drugs and potentially turn normal doses into toxic ones. Now, the scientist who first identified this problem finds grapefruit and other common fruit juices can do the opposite – significantly decrease the absorption of drugs, potentially canceling out the benefits of lifesaving medications, such as those that treat heart disease, cancer, organ-transplant rejection, and infection.

In the new study, David G. Bailey, Ph.D. and researchers at the University of Western Ontario in London, Ontario had healthy volunteers take the antihistamine, fexofenadine. Participants took the drug with either a single glass of grapefruit juice, water alone, or water with naringin – a substance in grapefruit juice that gives it that bitter taste.
 

Results show when fexofenadine was taken with grapefruit juice, only half of the drug was absorbed compared to when it was taken with water alone.
 

Other findings: grapefruit, orange and apple juices have been shown to lower the absorption of the anticancer drug, etoposide; some beta blockers (atenolol, celiprolol, talinolol) that treat high blood pressure and prevent heart attacks; cyclosporine, a drug that prevents the rejection of transplanted organs; and certain antibiotics (ciprofloxacin, levofloxacin, itraconazole).

Bailey says more drugs are likely to be added to the list as physicians become more aware of this drug-lowering interaction.

He advises patients to talk to their doctor or pharmacist before taking any medications with grapefruit juice or other fruits and juices.

SOURCE: 236th National Meeting of the American Chemical Society in Philadelphia, Pennsylvania, August 17-21, 2008