Occupancy of the Internal and External Pools of Glycoprotein IIb/IIIa following Abciximab Bolus and Infusion

The internal pool of GPIIb/IIIa, which is expressed upon platelet activation, may be inaccessible to inhibition by GPIIb/IIIa an-tagonists. To determine the occupancy of the internal and external pools of GPIIb/IIIa and platelet function following an abciximab bolus and infusion, 15 patients undergoing elective percutaneous transluminal coronary angioplasty were adminis-tered abciximab as a bolus and 36-h infusion. GPIIb/IIIa recep-tor number and occupancy in resting and TRAP-6 (20 mM)-activated samples (to expose the internal pool of GPIIb/IIIa) was quantified using a monoclonal antibody-based assay. Antibody binding was quantified by flow cytometry and platelet inhibition by light transmittance aggregation and by the rapid platelet function analyser (Accumetrics, San Diego, CA). The target of.80 % receptor occupancy (range 82–99 % occupancy) of the external pool of GPIIb/IIIa was achieved in all patients at 3 min