Make Patients Aware of Grapefruit’s Adverse Effects

Posted by Pharmacist on February 11, 2013

Many people are aware of the potential hazards of grapefruit interactions with prescription medication. These effects can include bone marrow suppression, renal toxicity, kidney failure, respiratory failure, internal bleeding and even sudden death. And while the number of drugs that can have negative interactions with grapefruit are on the rise, the Canadian Medical Association Journal (CMAJ) reports many doctors are not up to date.


Dr. David Bailey, Lawson Health Research Institute, London, Ontario wrote in a recent study that the number of drugs with the potential for serious adverse effects due to grapefruit has grown from 17 in 2008 to 43 in 2012; in total there are more than 85 drugs that can interact with grapefruit.


The study notes that patients typically do not volunteer information about their specific dietary habits and “Unless health care professionals are aware of the possibility that the adverse event they are seeing might have an origin in the recent addition of grapefruit to the patient’s diet, it is very unlikely that they will investigate it.” This is why it’s doubly important for patients to talk to their pharmacist and other health care providers about potential issues.


The active ingredients (furanocoumarins) innate to grapefruit, limes, pomelos and Seville oranges cause the interaction by irreversible inhibition of the drug metabolizing CYP3A4 enzyme that normally inactivates the effects of an estimated 50% of all medication. There are three characteristics of drugs that interact with these chemicals: they undergo drug metabolism in the gastrointestinal tract by CYP3A4, they’re administered orally and they have a low to intermediate bioavailability (the percentage of the oral dose of the drug that’s absorbed into the blood circulation is unchanged).


It’s important to note the adverse effects can happen even if several hours pass between eating the fruit and taking the drugs.


For more information:


List of drugs whose effects are decreased by grapefruit

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