More Drugs Adversely Affected by Grapefruit
Byline: Jennifer LaRue Huget Special to The Washington Post
Twenty years ago, Canadian researchers discovered that grapefruit interferes with the body's metabolism of certain drugs, including the immunosuppressant cyclosporine and at least one drug used to treat high blood pressure.
The same group of scientists has reported that the number of drugs on the market that react adversely with grapefruit has increased substantially in recent years -- from 17 to 43. The list includes cholesterol-lowering statins such as Zocor and Lipitor and blood pressure medications such as Nifediac and Afeditab, the study notes.
Chemicals found in grapefruit change the way these medications are metabolized in the gastrointestinal tract, dramatically increasing concentrations of the drug in the bloodstream. Those chemicals, called furanocoumarins, are also present in other citrus fruits, including Seville oranges -- the kind often used to make marmalade -- and limes and pomelos, according to the study.
The amount of grapefruit that can set off a reaction varies from drug to drug, the study notes, but in many cases, around 8 ounces of juice or a whole grapefruit "has sufficient potency to cause a pertinent pharmacokinetic interaction."
The drugs in question have three common traits: They're all taken orally; they all have limited bioavailability (which means that only small percentages of the active drug make it into the bloodstream under normal circumstances); and they all interact in the GI tract with an enzyme called CYP3A4. …