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.
References
- 1.Maskalyk J. Grapefruit juice: potential drug interactions. CMAJ 2002;167(3):279-80. [PMC free article] [PubMed]
- 2.Spence JD. Drug interactions with grapefruit juice: Whose responsibility is it to warn the public? Clin Pharmacol Ther 1997;61:395-400. [DOI] [PubMed]
- 3.Bailey DG, Spence JD, Munoz C, Arnold JM. Interaction of citrus juices with felodipine and nifedipine. Lancet 1991;337:268-9. [DOI] [PubMed]
- 4.Vincent J, Harris SI, Foulds G, Dogolo LC, Willavize S, Friedman HL. Lack of effect of grapefruit juice on the pharmacokinetics and pharmacodynamics of amlodipine. Br J Clin Pharmacol 2000;50(5):455-63. [DOI] [PMC free article] [PubMed]
- 5.Kantola T, Kivisto KT, Neuvonen PJ. Grapefruit juice greatly increases serum concentrations of lovastatin and lovastatin acid. Clin Pharmacol Ther 1998;63(4):397-402. [DOI] [PubMed]
- 6.Lilja JJ, Kivisto KT, Neuvonen PJ. Grapefruit juice–simvastatin interaction: effect on serum concentrations of simvastatin, simvastatin acid, and HMG-CoA reductase inhibitors. Clin Pharmacol Ther 1998;64(5):477-83. [DOI] [PubMed]
- 7.Lilja JJ, Kivisto KT, Neuvonen PJ. Grapefruit juice increases serum concentrations of atorvastatin and has no effect on pravastatin. Clin Pharmacol Ther 1999;66(2):118-27. [DOI] [PubMed]