Mechanism of Action

Eptifibatide reversibly inhibits platelet aggregation by preventing the binding of fibrinogen, von Willebrand factor, and other adhesive ligands to GP IIb/IIIa. When administered intravenously, eptifibatide inhibits ex vivoplatelet aggregation in a dose- and concentration-dependent manner. Platelet aggregation inhibition is reversible following cessation of the eptifibatide infusion; this is thought to result from dissociation of eptifibatide from the platelet.

Pharmacodynamics

Infusion of eptifibatide into baboons caused a dose-dependent inhibition of ex vivo platelet aggregation, with complete inhibition of aggregation achieved at infusion rates greater than 5.0 µg/kg/min. In a baboon model that is refractory to aspirin and heparin, doses of eptifibatide that inhibit aggregation prevented acute thrombosis with only a modest prolongation (2- to 3-fold) of the bleeding time. Platelet aggregation in dogs was also inhibited by infusions of eptifibatide, with complete inhibition at 2.0 µg/kg/min. This infusion dose completely inhibited canine coronary thrombosis induced by coronary artery injury (Folts model).

Human pharmacodynamic data were obtained in healthy subjects and in patients presenting with unstable angina (UA) or non-ST-segment elevation myocardial infarction (NSTEMI) and/or undergoing percutaneous coronary interventions. Studies in healthy subjects enrolled only males; patient studies enrolled approximately one-third women. In these studies, eptifibatide inhibited ex vivo platelet aggregation induced by adenosine diphosphate (ADP) and other agonists in a dose- and concentration-dependent manner. The effect of eptifibatide was observed immediately after administration of a 180-µg/kg intravenous bolus. Table 1 shows the effects of dosing regimens of eptifibatide used in the IMPACT II and PURSUIT studies on ex vivo platelet aggregation induced by 20 µM ADP in PPACK-anticoagulated platelet-rich plasma and on bleeding time. The effects of the dosing regimen used in ESPRIT on platelet aggregation have not been studied.

Table 1: Platelet Inhibition and Bleeding Time

The eptifibatide dosing regimen used in the ESPRIT study included two 180-µg/kg bolus doses given 10 minutes apart combined with a continuous 2.0 µg/kg/min infusion.

When administered alone, eptifibatide has no measurable effect on prothrombin time (PT) or activated partial thromboplastin time (aPTT). (See also PRECAUTIONS: DRUG INTERACTIONS.)

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