Source: DGNews  |  Posted 9 years ago

By Roberta Friedman, PhD
Special to DG News

SAN FRANCISCO, CA -- September 23, 2002 -- The United States Food and Drug Administration (FDA) is mounting a search for more drugs that may have their metabolic disposition upset by concurrent consumption of grapefruit, according to a report here at the 31st Annual Meeting of the American College of Clinical Pharmacology (ACCP). Fifteen or more drugs already are labelled to reflect the grapefruit interaction.

Dr. Toni Piazza-Hepp of the FDA presented a poster that included speculation on the way grapefruit interferes with drug absorption: by blocking cytochrome P450 in the intestine, or perhaps by active transporter systems such as the P-glycoprotein or organic anion transporter polypeptide. If a drug has a large first pass effect, consuming grapefruit could cause a higher drug dose to enter the bloodstream through any of these actions.

Two drugs Dr. Piazza-Hepp cited as coming recently under suspicion are amlodipine, a calcium channel blocker, and atorvastatin, a cholesterol-lowering agent. These drugs are not currently labelled to warn of an interaction, but "it looks like the data are warranting looking further" at the possibility of an interaction, he said. Reports in the literature, as well as in the FDA-maintained database of adverse event reporting, suggest these and other drugs could have a grapefruit interaction.

Clinicians have various options if a drug shares metabolic routes with grapefruit. If a patient is stabilised already on a particular drug, it may not be in the patient