Growing Number of Drugs Possibly Inhibited by Grapefruit

All drugs orally administered; have low-to-intermediate bioavailability; metabolized by CYP3A4

TUESDAY, Nov. 27 (HealthDay News) -- There are increasing numbers of newly marketed drugs that have the potential to interact with grapefruit, all of which are metabolized by the cytochrome P450 3A4 enzyme (CYP3A4), according to a review published online Nov. 26 in CMAJ, the journal of the Canadian Medical Association.

David G. Bailey, Ph.D., from the Lawson Health Research Institute in London, Canada, and colleagues conducted a systematic review of the literature, mainly randomized controlled trials, to examine the scientific concepts and clinical implications of the grapefruit-drug interaction.

The researchers identified more than 85 drugs with the potential to interact with grapefruit, 43 of which have interactions that can trigger serious adverse effects. Characteristics of drugs that interact with grapefruit include: oral administration; very low-to-intermediate absolute bioavailability; and all are metabolized by CYP3A4. In the gastrointestinal tract, grapefruit and certain related citrus fruits can irreversibly inhibit CYP3A4. Older patients are the most vulnerable to adverse clinical effects and have the greatest possibility of ingesting grapefruit and interacting medications.

"Grapefruit and certain other citrus fruits represent examples of foods generally considered to be healthful, but with the potential for a pharmacokinetic interaction causing greatly enhanced oral drug bioavailability," the authors write. "The current trend of increasing numbers of newly marketed grapefruit-affected drugs possessing substantial adverse clinical effects necessitates an understanding of this interaction and the application of this knowledge for the safe and effective use of drugs in general practice."

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