Journal of Invasive Cardiology

Tirofiban produces a smaller incidence of thrombocytopenia than abciximab, with varying reports on the incidence of the condition. In PRISM (Platelet Receptor Inhibition in Ischemic Syndrome Management), a study of 3,232 unstable angina patients, thrombocytopenia occurred more frequently with tirofiban than with heparin (1.1% versus 0.4%; p = 0.04),²⁶ but the RESTORE (Randomized Efficacy Study of Tirofiban for Outcomes and Efficacy) trial of 2,139 patients undergoing balloon angioplasty or directional atherectomy failed to show a significant difference in the incidence of thrombocytopenia between tirofiban and placebo (1.1% versus 0.9%; p = 0.709).27 This may have more to do with the higher incidence of thrombocytopenia accompanying PCI alone than in the former study. Figure 1 illustrates the rates of severe thrombocytopenia of platelet counts < 50,000/µl) in 5 major trials of GP IIb/IIIa inhibitors.

Readministration of GP IIb/IIIa antagonists may further increase the incidence of thrombocytopenia and profound thrombocytopenia. Five hundred patients who received abciximab for at least a second time during PCI were studied at 22 centers. Although there were no cases of hypersensitivity, thrombocytopenia of < 100,000/µl occurred in 4.6% of these patients, which is not markedly different from some of the incidences previously reported; however, profound thrombocytopenia with platelet counts of < 20,000/µl occurred in a greater percentage of patients (2.4%).²⁸ In addition, this study observed the antibody response specifically and demonstrated that although 4.8% of patients demonstrated the antibody after initial administration, an additional 19% of patients demonstrated the antibody after the first re-administration of the drug. The authors concluded that platelet counts should be followed closely in patients receiving abciximab readministration, and perhaps beyond the first 24 hours due to the timing of thrombocytopenia witnessed. The authors made no conclusion as to whether alternative GP IIb/IIIa receptor antagonists should be considered when readministration is necessary, but tirofiban has been used safely in a patient who developed profound thrombocytopenia in response to prior abciximab therapy.²⁹

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