Dr. David Bailey from the University of Western Ontario in London, Canada reported the “grapefruit effect” more than 15 years ago — grapefruit juice increases levels of the high-blood-pressure drug felodipine (Plendil), causing potentially dangerous effects.

Now, during the National Meeting of the American Chemical Society, he reports more juice-drug interactions.

First, the details.

  • Healthy volunteers swallowed the antihistamine fexofenadine (Allegra) with either a single glass of grapefruit juice, water containing only naringin (gives grapefruit juice its bitter taste), or water.

And, the results.

  • When taken with grapefruit juice, only half of fexofenadine was absorbed compared to taking the drug with water
  • Less fexofenadine was absorbed when swallowed with naringin-containing water.
  • The interactions appears to be due to naringin — a flavonoid glycoside in grapefruit — which blocks the action of organic anion-transporting polypeptide 1A2 (OATP1A2) to transfer drugs through the small intestine into the bloodstream.

The bottom line?
Dr. Bailey found that orange and apple juices decrease absorption of several important medications too.

  • The allergy drug fexofenadine (Allegra)
  • The antibiotics ciprofloxacin (Cipro, Proquin), levofloxacin (Levaquin), and itraconazole (Sporanox)
  • The beta-blocker blood pressure drugs atenolol (Tenormin), celiprolol (Cardem), and talinolol
  • The transplant-rejection drug cyclosporine (Gengraf, Neoral)
  • The cancer chemotherapy etoposide (Toposar, Vepesid)

Remember, none of this should be confused with the ability of grapefruit to raise blood levels of certain drugs by inhibiting the effect of the liver drug-metabolizing enzyme CYP450. See the list here. For this interaction, a glass of grapefruit juice is enough to suppress CYP3A4 activity by half, and the effect lasts for 12 to 24 hours.

It’s not clear how long the effect of grapefruit on OATP1A2 lasts.

9/9/08 17:55 JR

Hi, I’m JR

John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at www.Vicus.com, a complementary and alternative medicine website.