I was glad to see James Maskalyk's review of grapefruit and drug interactions,1 as I have been concerned for some time about the need to increase awareness of this issue.2,3 However, I would like to comment on drugs that were listed as if the effects were equal. Some patients enjoy grapefruit, and it is unkind to impose an unnecessary prohibition.
The magnitude of the grapefruit effect is related to the bioavailability of the drug. Felodipine, with a bioavailability of only 15%, had on average a tripling of blood levels with grapefruit, whereas nifedipine, with a bioavailability of 60%, had only a 30% increase in area under the curve (AUC). Amlodipine, which is approximately 80% bioavailable, is hardly affected by grapefruit.4 Similarly, whereas simvastatin and lovastatin, which are only 5% bioavailable, have a 15-fold increase in AUC with grapefruit,5,6 levels of atorvastatin increase only by 2.5-fold.7
I therefore tend to tell patients on amlodipine and atorvastatin that grapefruit is likely to have only a minor effect.
J. David Spence Stroke Prevention and Atherosclerosis Research Centre Robarts Research Institute London, Ont.
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