Grapefruits are second only to oranges as Americas' favorite citrus fruit. Loaded with vitamin A, vitamin C, potassium, calcium and magnesium, grapefruits are nutritious as well as tasty, and they are the namesake for the popular Grapefruit Diet, a weight-loss program that has been around since the 1930s. However, per capita grapefruit consumption in the United States has fallen 50 percent in the last 30 years, in large part due to the discovery that grapefruit interferes with the metabolism of many medications.
Enzyme Blockade
Drug metabolism is a complex process. These foreign and potentially toxic substances must all eventually be broken down and eliminated from your body. For many medications, this degradation begins when they are exposed to an enzyme called CYP3A4, which is found in the cells lining your gastrointestinal tract. According to the September 2010 issue of "Cardiovascular Journal of Africa," CYP3A4 metabolizes over 60 percent of commonly prescribed drugs. Grapefruit blocks CYP3A4, thus inhibiting its ability to break down medications before they enter your bloodstream.
Increased Toxicity
The development of new pharmaceutical agents includes human studies that allow drug manufacturers to determine dosages that are both effective and safe. However, once new medications are on the market, unexpected interactions with other drugs or foods often occur. Although not all interactions between grapefruit and medications are clinically relevant, grapefruit's interference with CYP3A4 can cause marked increases in the amounts of drugs entering your bloodstream. In some cases, this can significantly increase your chances for adverse side effects and even lethal toxicities.
Drugs Affected
The list of medications that are affected by grapefruit is continually expanding. Following the 1989 discovery of grapefruit's interaction with the blood pressure drug felodipine, numerous additional agents were soon found to be similarly affected. Antihypertensives, medications for abnormal heart rhythms, cholesterol-lowering agents, sedatives, birth control pills and other hormones, immunosuppressants, HIV drugs, antidepressants, antihistamines, asthma drugs, antipsychotic agents, anticonvulsants and medicines for erectile dysfunction are all among the prescription medications possibly affected by grapefruit. In most cases, this interaction raises your blood concentration of the drug in question, sometimes to dangerous levels.
Considerations
Grapefruit interferes with the intestinal metabolism of a wide variety of medications. In some cases, this food-drug interaction can significantly increase blood levels of your medication and heighten the risk for side effects. The intensity of grapefruit's effect varies from person to person, depending on your genetic makeup and the amount of CYP3A4 in your intestine. An August 2006 "American Family Physician" review reported that grapefruit's inhibition of CYP3A4 can last up to 72 hours. Therefore, separating your grapefruit consumption from your medication administration by several hours will not prevent this interaction. If you take a prescription medication, ask your doctor if grapefruit is safe for you.
References
- U.S. Department of Agriculture Economic Research Service
- "Cardiovascular Journal of Africa"; The Grapefruit: An Old Wine in a New Glass? Metabolic and Cardiovascular Perspectives; P.M. Owira, J.A. Ojewole; Sept-Oct 2010
- The People's Pharmacy: Graedon's Guide to Grapefruit Interactions
- "American Family Physician"; Management of Grapefruit-Drug Interactions; A.L. Stump, et al.; August 2006
Member Comments