Assessment of a candidate marker constituent predictive of a dietary substance-drug interaction: case study with grapefruit juice and CYP3A4 drug substrates

J Pharmacol Exp Ther. 2014 Dec;351(3):576-84. doi: 10.1124/jpet.114.216838. Epub 2014 Sep 24.


Dietary substances, including herbal products and citrus juices, can perpetrate interactions with conventional medications. Regulatory guidances for dietary substance-drug interaction assessment are lacking. This deficiency is due in part to challenges unique to dietary substances, a lack of requisite human-derived data, and limited jurisdiction. An in vitro-in vivo extrapolation (IVIVE) approach to help address some of these hurdles was evaluated using the exemplar dietary substance grapefruit juice (GFJ), the candidate marker constituent 6',7'-dihydroxybergamottin (DHB), and the purported victim drug loperamide. First, the GFJ-loperamide interaction was assessed in 16 healthy volunteers. Loperamide (16 mg) was administered with 240 ml of water or GFJ; plasma was collected from 0 to 72 hours. Relative to water, GFJ increased the geometric mean loperamide area under the plasma concentration-time curve (AUC) significantly (1.7-fold). Second, the mechanism-based inhibition kinetics for DHB were recovered using human intestinal microsomes and the index CYP3A4 reaction, loperamide N-desmethylation (KI [concentration needed to achieve one-half kinact], 5.0 ± 0.9 µM; kinact [maximum inactivation rate constant], 0.38 ± 0.02 minute(-1)). These parameters were incorporated into a mechanistic static model, which predicted a 1.6-fold increase in loperamide AUC. Third, the successful IVIVE prompted further application to 15 previously reported GFJ-drug interaction studies selected according to predefined criteria. Twelve of the interactions were predicted to within the 25% predefined criterion. Results suggest that DHB could be used to predict the CYP3A4-mediated effect of GFJ. This time- and cost-effective IVIVE approach could be applied to other dietary substance-drug interactions to help prioritize new and existing drugs for more advanced (dynamic) modeling and simulation and clinical assessment.

Publication types

  • Clinical Trial, Phase II
  • Randomized Controlled Trial
  • Research Support, N.I.H., Extramural

MeSH terms

  • Adult
  • Beverages*
  • Biomarkers / blood
  • Citrus paradisi*
  • Cross-Over Studies
  • Cytochrome P-450 CYP3A / metabolism*
  • Female
  • Food-Drug Interactions / physiology*
  • Forecasting
  • Humans
  • Loperamide / administration & dosage
  • Loperamide / blood*
  • Male
  • Microsomes / drug effects
  • Microsomes / enzymology
  • Middle Aged
  • Prospective Studies
  • Substrate Specificity / drug effects
  • Substrate Specificity / physiology
  • Young Adult


  • Biomarkers
  • Loperamide
  • Cytochrome P-450 CYP3A
  • CYP3A4 protein, human