Grapefruit juice increases felodipine oral availability in humans by decreasing intestinal CYP3A protein expression

J Clin Invest. 1997 May 15;99(10):2545-53. doi: 10.1172/JCI119439.


The increase in oral availability of felodipine and other commonly used medications when taken with grapefruit juice has been assumed to be due to inhibition of CYP3A4, a cytochrome P450 that is present in liver and intestine. To evaluate the effect of repeated grapefruit juice ingestion on CYP3A4 expression, 10 healthy men were given 8 oz of grapefruit juice three times a day for 6 d. Before and after receiving grapefruit juice, small bowel and colon mucosal biopsies were obtained endoscopically, oral felodipine kinetics were determined, and liver CYP3A4 activity was measured with the [14C N-methyl] erythromycin breath test in each subject. Grapefruit juice did not alter liver CYP3A4 activity, colon levels of CYP3A5, or small bowel concentrations of P-glycoprotein, villin, CYP1A1, and CYP2D6. In contrast, the concentration of CYP3A4 in small bowel epithelia (enterocytes) fell 62% (P = 0.0006) with no corresponding change in CYP3A4 mRNA levels. In addition, enterocyte concentrations of CYP3A4 measured before grapefruit juice consumption correlated with the increase in Cmax when felodipine was taken with either the 1st or the 16th glass of grapefruit juice relative to water (r = 0. 67, P = 0.043, and r = 0.71, P = 0.022, respectively). We conclude that a mechanism for the effect of grapefruit juice on oral felodipine kinetics is its selective downregulation of CYP3A4 in the small intestine.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • ATP Binding Cassette Transporter, Subfamily B, Member 1 / metabolism
  • Administration, Oral
  • Adult
  • Aryl Hydrocarbon Hydroxylases*
  • Beverages*
  • Biopsy
  • Citrus*
  • Colon / cytology
  • Cytochrome P-450 CYP3A
  • Cytochrome P-450 Enzyme Inhibitors
  • Cytochrome P-450 Enzyme System / biosynthesis*
  • Cytochrome P-450 Enzyme System / metabolism
  • Felodipine / administration & dosage
  • Felodipine / pharmacokinetics*
  • Gene Expression
  • Humans
  • Intestinal Mucosa / cytology
  • Intestinal Mucosa / enzymology*
  • Intestine, Small / cytology
  • Kinetics
  • Liver / enzymology
  • Male
  • Mixed Function Oxygenases / antagonists & inhibitors
  • Mixed Function Oxygenases / biosynthesis*
  • Oxidoreductases, N-Demethylating / metabolism
  • Reference Values


  • ATP Binding Cassette Transporter, Subfamily B, Member 1
  • Cytochrome P-450 Enzyme Inhibitors
  • Cytochrome P-450 Enzyme System
  • Mixed Function Oxygenases
  • Aryl Hydrocarbon Hydroxylases
  • CYP3A protein, human
  • CYP3A5 protein, human
  • Cytochrome P-450 CYP3A
  • CYP3A4 protein, human
  • Oxidoreductases, N-Demethylating
  • Felodipine