Inhibitory effects of CYP3A4 substrates and their metabolites on P-glycoprotein-mediated transport

Eur J Pharm Sci. 2001 Feb;12(4):505-13. doi: 10.1016/s0928-0987(00)00215-3.


It is generally known that the substrates and/or inhibitors of cytochrome P450 (CYP) 3A4 and P-glycoprotein (P-gp) overlap with each other. In intestinal epithelial cells, it is surmised that the metabolites coexist with their parent drug. However, most studies on P-gp did not take the effects of those metabolites into consideration. Therefore, in the present study, we investigated the inhibitory effects of five substrates of CYP3A4 (nifedipine, testosterone, midazolam, amiodarone, and azelastine) and their metabolites on the P-gp-mediated transcellular transport. The transcellular transports of [(3)H]daunorubicin or [(3)H]digoxin by monolayers of LLC-GA5-COL150 cells in which P-gp was overexpressed were measured in the presence or absence of the CYP3A4 substrates and their metabolites. Nifedipine, testosterone, midazolam, and their metabolites exhibited no effects on the P-gp-mediated transport of [(3)H]daunorubicin and [(3)H]digoxin. On the other hand, the transport of [(3)H]daunorubicin was strongly inhibited by amiodarone, desethylamiodarone, azelastine, and desmethylazelastine, with IC(50) values of 22.5, 15.4, 16.0 and 11.8 microM, respectively. The transport of [(3)H]digoxin was also strongly inhibited by these compounds, with IC(50) values of 45.6, 25.2, 30.0 and 41.8 microM, respectively. Another metabolite of azelastine, 6-hydroxyazelastine, exhibited no effects on these transports. It was suggested that the CYP3A4 metabolites of which their parent drug exhibited inhibition on the P-gp-mediated transport are possibly also inhibitors. It would be possible more complicated drug-drug interactions would be caused by the metabolites as well as their parent drugs in the liver and the intestine via the inhibition of CYP3A4 and P-gp.

MeSH terms

  • ATP Binding Cassette Transporter, Subfamily B, Member 1 / drug effects
  • ATP Binding Cassette Transporter, Subfamily B, Member 1 / metabolism*
  • Amiodarone / metabolism
  • Amiodarone / pharmacology
  • Animals
  • Antibiotics, Antineoplastic / metabolism*
  • Calcium Channel Blockers / pharmacology
  • Cells, Cultured
  • Cytochrome P-450 CYP3A
  • Cytochrome P-450 Enzyme System / drug effects
  • Cytochrome P-450 Enzyme System / metabolism*
  • Daunorubicin / metabolism*
  • Digoxin / metabolism*
  • Enzyme Inhibitors / metabolism*
  • GABA Modulators / pharmacology
  • Gonadal Steroid Hormones / pharmacology
  • Humans
  • LLC-PK1 Cells / drug effects
  • LLC-PK1 Cells / metabolism
  • Midazolam / pharmacology
  • Mixed Function Oxygenases / drug effects
  • Mixed Function Oxygenases / metabolism*
  • Nifedipine / pharmacology
  • Phthalazines / metabolism
  • Phthalazines / pharmacology
  • Swine
  • Testosterone / pharmacology


  • ATP Binding Cassette Transporter, Subfamily B, Member 1
  • Antibiotics, Antineoplastic
  • Calcium Channel Blockers
  • Enzyme Inhibitors
  • GABA Modulators
  • Gonadal Steroid Hormones
  • Phthalazines
  • Testosterone
  • Digoxin
  • Cytochrome P-450 Enzyme System
  • Mixed Function Oxygenases
  • CYP3A protein, human
  • Cytochrome P-450 CYP3A
  • CYP3A4 protein, human
  • Nifedipine
  • Amiodarone
  • Midazolam
  • azelastine
  • Daunorubicin