Semi‐Mechanistic Modelling and Simulation of Inhibition of Platelet Aggregation by Antiplatelet Agents

Antiplatelet agents are a class of pharmaceuticals that decrease platelet aggregation and thus inhibit thrombus formation. We examined the relationships between plasma concentrations of antiplatelet agents (triflusal, clopidogrel and cilostazol) and the platelet aggregation inhibitory effect after dosing. We used triflusal, cilostazol and clopidogrel for the development of a semi‐mechanistic PK/PD model. The drugs chosen are used widely and reflect various mechanisms of antiplatelet agents. Time courses of plasma concentrations of the antiplatelet agents and their platelet aggregation effects were analysed using ADPAT V. Pharmacokinetic profiles were fitted to an extended parent–metabolite pharmacokinetic model, based on a two‐compartment model, and the pharmacodynamic effects of the agents were fitted to a platelet aggregation effect model that consisted of the following parameters: Ks, the active‐form platelet synthesis rate constant; K, the apparent reaction rate constant of the agent and active‐form platelets; Kel‐PRP, the apparent rate constant of platelets; and ε, an intrinsic activity parameter. This semi‐mechanistic PK/PD model described well the relationship between plasma concentrations of antiplatelet agents and platelet aggregation effects. In addition, the estimated parameters were suitable for the explanation of the agents and also have a good correlation with platelet characteristics, such as platelet half‐life and platelet aggregation baseline effects. Specifically, we discovered the strong correlations between estimated K parameter and in vitro drug activity. We conclude that this semi‐mechanistic PK/PD model explained drug PK/PD characteristics well and will be useful for accurate predictions of antiplatelet effect in the clinical situations.