Grapefruit Juice-Vinblastine Interaction

ALEXANDRIA, Virginia—Drinking grapefruit juice with certain medications, including at least one widely used in cancer treatment, may inhibit their absorption, according to an in vitro study in the April 1999 issue of Pharmaceutical Research, a publication of the American Association of Pharmaceutical Scientists (AAPS).

The drugs include vinblastine, cyclosporine (Sandimmune, Neoral), losartan (Cozaar, an antihypertension agent), digoxin, and fexofenadine (Allegra, an antihistamine).

This inhibition occurs, the researchers said, because an unknown substance in grapefruit juice activates one of the body’s naturally produced drug efflux mechanisms, P-glycoprotein, located in the intestinal tract. When grapefruit juice interacts with P-glycoprotein, the result is an increased likelihood that certain drugs will be stopped from entering the bloodstream.