Ticlopidine decreases the in vivo activity of CYP2C19 as measured by omeprazole metabolism

Br J Clin Pharmacol. 1999 Apr;47(4):454-7. doi: 10.1046/j.1365-2125.1999.00914.x.


Aims: To examine the effect of ticlopidine administration on the activities CYP2C19 and CYP3 A in vivo using omeprazole as a model substrate.

Methods: A single dose of 40 mg omeprazole was administered orally with or without ticlopidine (300 mg daily for 6 days) to six Japanese extensive metabolisers with respect to CYP2C19. Blood samples were taken for the measurement of plasma concentrations of omeprazole, 5-hydroxyomeprazole and omeprazole sulphone.

Results: Ticlopidine administration increased omeprazole Cmax (1978+/-859/ 3442+/-569 (control phase/ticlopidine phase, nm )) and decreased the oral clearance of omeprazole (CL/F; 25.70+/-16. 17/10.76+/-1.16 (control phase/ticlopidine phase, l h-1 )) significantly. The 5-hydroxyomeprazole to omeprazole AUC ratio (0. 817+/-0.448/0.236+/-0.053 (control phase/ticlopidine phase)) and the 5-hydroxyomeprazole to omeprazole sulphone AUC ratio (1.114+/-0. 782/0.256+/-0.051 (control phase/ticlopidine phase)) were decreased significantly after ticlopidine administration. The decrease in omeprazole CL/F and the 5-hydroxyomeprazole to omeprazole AUC ratio correlated significantly with their respective absolute values when the drug was given alone. The decrease in CL/F following ticlopidine administration correlated with that in the 5-hydroxyomeprazole to omeprazole AUC ratio.

Conclusions: These findings suggest that ticlopidine inhibited the in vivo activity of CYP2C19, but not, or to a lesser extent CYP3 A4, and that the magnitude of inhibition by ticlopidine is related to the in vivo activity of CYP2C19 before inhibition.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Aryl Hydrocarbon Hydroxylases*
  • Cross-Over Studies
  • Cytochrome P-450 CYP2C19
  • Cytochrome P-450 CYP3A
  • Cytochrome P-450 Enzyme Inhibitors*
  • Cytochrome P-450 Enzyme System / metabolism
  • Enzyme Inhibitors / pharmacology*
  • Humans
  • Male
  • Mixed Function Oxygenases / antagonists & inhibitors*
  • Mixed Function Oxygenases / metabolism
  • Omeprazole / metabolism*
  • Platelet Aggregation Inhibitors / pharmacology*
  • Ticlopidine / pharmacology*


  • Cytochrome P-450 Enzyme Inhibitors
  • Enzyme Inhibitors
  • Platelet Aggregation Inhibitors
  • Cytochrome P-450 Enzyme System
  • Mixed Function Oxygenases
  • Aryl Hydrocarbon Hydroxylases
  • CYP2C19 protein, human
  • CYP3A protein, human
  • Cytochrome P-450 CYP2C19
  • Cytochrome P-450 CYP3A
  • Omeprazole
  • Ticlopidine