Grapefruit and Other Juices May Affect Absorption of Some Medications

Aug. 20, 2008 — A new study has found that grapefruit juice, long known to boost the absorption of certain medications, is not the only juice that does not mix well with medications, according to the researcher who first identified the ill effects of grapefruit juice.

Scientists and consumers have known for years that grapefruit juice can increase the absorption of some medications — with the potential for turning normal doses into toxic overdoses.

Now it has been found that grapefruit and other common fruit juices, including orange and apple, can have the opposite effect by substantially decreasing the absorption of other medications, potentially wiping out their beneficial effects.

David Bailey, Ph.D., a professor of medicine and pharmacology at the University of Western Ontario, in London, Ontario, Canada presented his findings this week at the American Chemical Society's national meeting, in Philadelphia.

New Study Builds on Previous Research
"The original finding is that [grapefruit juice] markedly boosts the amount of drug that gets into the bloodstream," Dr. Bailey says. He first reported that nearly 20 years ago when he discovered that grapefruit juice increased the body's blood levels of the drop felodipine (Plendil), used to treat high blood pressure.

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

As a result of the so-called "Grapefruit Juice Effect," some prescription medications now carry warning labels against taking grapefruit juice or fresh grapefruit during medication consumption.

Physicians traditionally warn against drinking grapefruit juice if you are taking certain medications for high cholesterol, high blood pressure, and heart rhythm problems, according to the American Academy of Family Physicians (AAFP).

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

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

In each case, substances in the juices affected the absorption of the medications.

They found that the active ingredient of grapefruit juice, naringin, appears to block a key medication uptake transporter, called OATP1A2, involved in shuttling medications from the small intestine to the bloodstream. Blocking this transporter reduces medication absorption and neutralizes their potential benefits, the researchers say.

By contrast, medications whose levels are boosted in the presence of grapefruit juice appear to block an important drug metabolizing enzyme, called CYP3A4, that normally breaks down medications.

"We don't [yet] know all the drugs affected," Dr. Bailey says.

Take Medications With Water, Not Juice
Michael Gaunt, PharmD, is a medication safety analyst at the Institute for Safe Medication Practices in Horsham, Pa. He says, "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."

Dr. Bailey agrees. If you opt for water, he says, "a glass is better than a sip. It helps dissolve the tablet." And cool water is better than hot, he adds, because your stomach empties cool water faster, sending the medication on its way to the small intestine and finally the blood stream.

Always consult your physician or pharmacist for more information.