title: Population pharmacodynamic modelling of aspirin- and Ibuprofen-induced inhibition of platelet aggregation in healthy subjects.
abstract: OBJECTIVE
  The objective of this study was to develop a mechanism-based pharmacodynamic model that characterizes the antiplatelet effects of aspirin (acetylsalicylic acid) and ibuprofen alone and in combination.
  
  
  METHODS
  Ten healthy volunteers were enrolled in a single-blinded, randomized, three-way crossover study. Treatments consisted of single doses of oral aspirin (325 mg) and ibuprofen (400 mg) and concomitant administration of aspirin (325 mg) and ibuprofen (400 mg). Ex vivo whole blood platelet aggregation induced by collagen (1 microg/mL) or arachidonic acid (0.5 mmol/L) was measured by impedance aggregometry. Model development and population parameter estimation were performed using nonlinear mixed-effects modelling implemented in NONMEM.
  
  
  RESULTS
  Relatively complete inhibition of platelet aggregation was achieved following aspirin treatment (approximately 77% inhibition within 2 hours), and return to baseline values occurred within 72-96 hours after dosing. In contrast, treatment with ibuprofen alone or in combination with aspirin produced transient inhibition of platelet aggregation, with complete recovery observed in 6-8 hours. The final pharmacodynamic model was based on the turnover of cyclo-oxygenase-1 (COX-1) enzyme, and incorporated irreversible inhibition by aspirin and reversible binding and antiplatelet effects of ibuprofen. The temporal response profiles from all three study arms were well described by the final model, and the parameters were estimated with good precision. The apparent turnover rate constant for COX-1 (kout) and the irreversible inhibition rate constant for aspirin (K) were estimated to be 0.0209 h(-1) and 0.152 (mg/L)(-1).h(-1), with interindividual variability of 30.6% and 26.2%, respectively. Simulations were used to evaluate the influence of clinically relevant ibuprofen regimens on the antiplatelet effect of aspirin, confirming clinical reports that the antiplatelet effect of aspirin would be blocked when multiple daily doses of ibuprofen are given, even if taken after aspirin administration.
  
  
  CONCLUSIONS
  A mechanism-based pharmacodynamic model has been developed that characterizes the antiplatelet effects of aspirin and ibuprofen, alone and concomitantly, and predicts a significant inhibition of aspirin antiplatelet effects in the presence of a typical ibuprofen dosing regimen.
authors.affiliation: Department of Pharmaceutical Sciences, University at Buffalo, State University of New York, Buffalo, New York 14260, USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Hong
authors.forename: Fran M
authors.initials: FM
authors.lastname: Gengo
authors.forename: Michelle M
authors.initials: MM
authors.lastname: Rainka
authors.forename: Vernice E
authors.initials: VE
authors.lastname: Bates
authors.forename: Donald E
authors.initials: DE
authors.lastname: Mager
mesh_terms: D000284:Administration, Oral; D000328:Adult; D016718:Arachidonic Acid / Q000494:pharmacology; D001241:Aspirin / Q000097:blood / Q000493:pharmacokinetics / Q000494:pharmacology*; D003094:Collagen / Q000494:pharmacology; D018592:Cross-Over Studies; D016861:Cyclooxygenase Inhibitors / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology; D006207:Half-Life; D006801:Humans; D007052:Ibuprofen / Q000097:blood / Q000493:pharmacokinetics / Q000494:pharmacology*; D008875:Middle Aged; D008954:Models, Biological; D009010:Monte Carlo Method; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology; D016037:Single-Blind Method; D013997:Time Factors
chemical_list: D016861:Cyclooxygenase Inhibitors; D010975:Platelet Aggregation Inhibitors; D016718:Arachidonic Acid; D003094:Collagen; D001241:Aspirin; D007052:Ibuprofen