Efficacy of Abciximab Bolus Only Regimen in Providing Inhibition of Platelet Action Over Time (FABOLUS)

Based on the outcome of the EPIC trial, and the sub-optimal results with a single abciximab bolus compared with bolus and infusion, it was recommended to prolong platelet inhibition by a 12h infusion of abciximab after the initial bolus administration in patients undergoing percutaneous coronary intervention (PCI). However, lower outcomes in the single bolus group in the EPIC study were entirely driven by the rates of urgent repeat revascularization at 30 days (3•6 percent bolus group versus 0•8 percent bolus and infusion group, p < 0.001), a complication probably related to the lack of stent use at that time. Importantly, there was no significant difference in terms of death or myocardial infarction (MI). Moreover, the use of clopidogrel in patients undergoing coronary stenting may currently reduce the need for infusion after a single abciximab bolus and it is likely that the soon to come availably of even more potent oral thienopyridines with faster onset of action such as prasugrel may further contribute to make post-bolus abciximab infusion of marginal clinical benefit. Yet, it is known that infusion, as compared to bolus only regimen increases the bleeding rate and the incidence of thrombocytopenia. Thus, bolus only regimen has the potential to maintain protection from ischemic complications in patients undergoing PCI while optimizing the safety profile of the treatment in the current era of intervention based on stents and thienopyridines with fast onset of action.

The CLEAR-PLATELETS study has recently shown that 600 mg clopidogrel does not affect the degree of platelet inhibition throughout infusion of eptifibatide, which is consistent with the notion that glycoprotein IIb/IIIa inhibition at steady state leads to near maximal platelet blockade. No study has so far investigated the effect of clopidogrel, given at high loading dose, in patients treated with abciximab bolus only. In particular, it is not known whether the administration of clopidogrel at high loading dose may prolong the effect of abciximab bolus on the degree of platelet inhibition and if so at which time point the combination of abciximab bolus and clopidogrel may become suboptimal in terms of platelet inhibition as compared to currently recommended 12h infusion of abciximab after the initial bolus administration. This information would lead to relevant clinical implications as it may define the time frame for a safe and effective intervention after bolus only of abciximab in current practice.

This is a single-centre, double-blind prospective randomized pharmacodynamic investigation of 2 antiplatelet regimens in patients undergoing coronary stenting for non-ST segment elevation acute coronary syndromes (NSTECACS):

1. Abciximab bolus followed by infusion plus on-label clopidogrel administration at 300 mg loading dose.
2. abciximab bolus without infusion plus high loading dose of clopidogrel at 600 mg

The objective of the investigation is to test the hypothesis that the administration of abciximab bolus only plus high loading dose of clopidogrel at 600 mg will provide a non inferior level of inhibition of platelet aggregation 4 hours after administration as compared to abciximab bolus followed by standard infusion in combination with clopidogrel loading dose of 300 mg in patients with normal response to clopidogrel (as evaluated after 14-30 days).