I was struck by the similarity of a recent CMAJ editor's preface on drug interactions1 to a piece I wrote a couple of years ago.2 To date the drug interactions with grapefruit appear to include inhibition of gut wall cytochrome P450 3A4 by naringin and dihydroxybergamottin,3 as well as an interaction with P-glycoprotein.4 In the case of drug-drug interactions, there are mechanisms for warning physicians, pharmacists and patients. However, in the case of grapefruit, special efforts are required: grocers seldom take a drug history when dispensing grapefruit.
In the Australian state of Victoria, it has been required for some time that pharmacists provide warnings when dispensing some drugs with known grapefruit interactions5; however, not all drugs have been tested for the interaction.
A simple rule of thumb for anticipating grapefruit interaction with drugs is that if erythromycin is a problem, then grapefruit is a problem.
Acknowledgments
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