![]() ![]() In practice, numerous drugs interact with grapefruit juice. There is increasing evidence that transporter proteins such as organic anion transporters and P-glycoprotein are involved in interactions between drugs and grapefruit juice. Along with the variable composition of grapefruit juice, this makes it difficult to predict the magnitude and clinical consequences of drug interactions with grapefruit juice in a given patient. There are large inter-individual differences in enzyme efficiency. Drugs interacting with grapefruit and inducing serious clinical consequences (confirmed or very probable) include: immunosuppressants, some statins, benzodiazepines, most calcium channel blockers, indinavir and carbamazepine. Grapefruit juice also inhibits several other cytochrome P450 isoenzymes, but they are less frequently implicated in interactions with clinical consequences. This increases plasma concentrations of the drugs concerned, creating a risk of overdose and dose-dependent adverse effects. Grapefruit juice inhibits CYP3A4, the cytochrome P450 isoenzyme most often involved in drug metabolism. Clinical reports of drug interactions with grapefruit juice are supported by pharmacokinetic studies, each usually involving about 10 healthy volunteers, in which the probable clinical consequences were extrapolated from the observed plasma concentrations. ![]() Other grapefruit products are also occasionally implicated, including preserves, lyophylised grapefruit juice, powdered whole grapefruit, grapefruit seed extract, and zest. No single component accounts for all observed interactions. The components of grapefruit juice vary considerably depending on the variety, maturity and origin of the fruit, local climatic conditions, and the manufacturing process. Several serious adverse effects involving drug interactions with grapefruit juice have been published in detail. The study authors urge physicians to learn more about drug interactions with grapefruit (Thompson, " Shots," NPR, 11/27 United Press International, 11/27 Brown, " Booster Shots," Los Angeles Times, 11/27).Since the late 1980s, grapefruit juice has been known to affect the metabolism of certain drugs. The study notes that grapefruits are not the only fruits to cause problems with medications: Seville oranges, pomelos, and limes also contain the same family of disruptive compounds. Popular drugs that interact negatively with grapefruit include various antibiotics, as well as drugs that treat hypertension, high cholesterol, and cancer. "Taking one tablet with a glass of grapefruit juice is like taking five tablets with water," Bailey says. ![]() This can effectively cause a medication overdose. When the enzyme doesn't function normally, medications may not degrade and instead circulate in the blood at higher levels than normal. The chemical culprits in grapefruits are called furanocoumarins, which deactivate an enzyme found in the small intestine and liver that breaks down various toxins and an estimated 50% of all drugs. ![]() Writing in the Canadian Medical Association Journal, Lawson Health Research Institute's David Bailey-who first discovered that the bitter fruit can interact with drugs more than 20 years ago-and colleagues reported that the number of drugs that can interact harmfully with grapefruit has increased from 17 to 43 in the last four years. A new study identifies as many as 85 common medications that interact with grapefruit, and at least 43 such interactions can have serious side effects-including sudden death, kidney failure, and internal bleeding. ![]()
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