Grapefruit juice, long known to boost the absorption of certain medications, isn't the only juice that sometimes doesn't mix well with drugs, according to the Canadian researcher who first identified that effect of grapefruit juice.

Other common juices, including orange and apple, may limit the body's absorption of drugs, compromising their effectiveness, said David Bailey, a professor of medicine and pharmacology at the University of Western Ontario, in London, Ontario.

Bailey's research was scheduled for presentation yesterday at the American Chemical Society's national meeting, in Philadelphia.

"The original finding is that (grapefruit juice) ... markedly boosts the amount of drug that gets into the bloodstream," Bailey said.

He first reported that nearly 20 years ago, when he discovered that grapefruit juice increased the blood levels of the drop felodipine (Plendil), used to treat high blood pressure.

Since that original finding, other researchers have identified dozens of other medications that could interact adversely with grapefruit juice, Bailey said.

Doctors generally warn against drinking grapefruit juice if you're taking certain medications for high cholesterol, high blood pressure and heart rhythm problems, according to the American Academy of Family Physicians.

In his latest research, Bailey found that orange, apple and grapefruit juice can each lower the body's absorption of such medications as the anti-cancer drug etoposide (Etopophos, Vepesid); certain beta blockers, like tenormin (Atenolol) and talinolol (Cordanum), used to treat high blood pressure and prevent heart attacks; cyclosporine, used to prevent organ transplant rejection; and some antibiotics, including ciprofloxacin (Cipro), levofloxacin (Levaquin) and itraconazole (Sporanox).

Bailey also found that healthy volunteers who took the allergy drug fexofenadine (Allegra) with grapefruit juice absorbed only half the amount of the drug as did volunteers who took the medicine with water.

In each case, substances in the juices affect the absorption of the drugs.

Some chemicals block a drug uptake transporter, reducing absorption of medicine; other chemicals block a drug metabolizing enzyme that normally breaks down the drugs, he said.

"We don't (yet) know all the drugs affected," Bailey said.

Michael Gaunt is a medication safety analyst at the Institute for Safe Medication Practices in Horsham, Pa.

He said, "If this study holds true (in future research), you are going to have to warn people in a similar fashion" about other juices.

Gaunt's advice for now: "In general, it's safest to take medication with water."

Bailey agreed. If you opt for water, he said, "a glass is better than a sip. It helps dissolve the tablet."

And cool water is better than hot, he added, because your stomach empties cool water faster, sending the medication on its way to the small intestine and finally the bloodstream.

Learn more:

American Academy of Family Physicians: www.familydoctor.org