The clinical impact of platelet glycoprotein IIb/IIIa receptor blockade in cardiovascular medicine

Effect of tirofiban on C-reactive protein in non-ST–elevation myocardial infarction

OBJECTIVES

C-reactive protein (CRP) is a prototypic marker of inflammation. The effect of tirofiban on CRP levels in patients with non-ST-elevation myocardial infarction (NSTEMI) was investigated.

METHODS

The present study was prospective and randomized. Patients with NSTEMI received aspirin, clopidogrel, statin, and unfractionated heparin. Patients with NSTEMI were enrolled into either the tirofiban + heparin group (group 1: n = 25) or the heparin group (group 2: n = 32). Levels of CRP were determined at baseline and after 48 and 72 hours. Heparin and tirofiban were discontinued after 48 hours.

RESULTS

Levels CRP of were similar in two groups at baseline; they increased significantly at 48 hours and 72 hours in the control group but not in the tirofiban group. The differences on and after treatment were statistically significant. In group 1, CRP elevation was attenuated after tirofiban infusion compared with group 2.

CONCLUSIONS

Products of platelet activation may aid neutrophil accumulation and enhance inflammation. Activated leukocytes and platelets potentate each others' effects. Tirofiban strongly inhibits the platelet aggregation. The decreased platelet aggregation can suppress the inflammatory protein, chemokine, and adhesion molecule expression. After the tirofiban infusion, CRP elevation was atteunated in patients with NSTEMI.

Platelet kinetics in dogs treated with a glycoprotein IIb/IIIa peptide antagonist

Platelet glycoprotein IIb/IIIa (GPIIb/IIIa) receptor antagonists have been highly effective inhibitors of platelet aggregation in preclinical studies and in clinical trials. However, decreased platelet counts have been documented in preclinical studies and in some patients receiving GPIIb/IIIa antagonists. We evaluated changes in platelet kinetics and fate in dogs receiving the GPIIb/IIIa receptor antagonist RPR 109891 orally for 4 days. Dogs receiving RPR 109891 had a 22-52% decrease in platelet count with the nadirs at 3-5 days after initiation of treatment. Platelet survival time was reduced by 19%, and platelet half-life was reduced by 63%. Indium-111-labeled platelets were rapidly cleared from the blood within 1 hour after administration of RPR 109891 on treatment days 1 and 2. This clearing was associated with a sharp increase in radioactivity in spleen but not in liver or lung. Platelet clearance was markedly attenuated on treatment days 3 and 4. Platelet counts returned to baseline within 1 week after discontinuation of treatment. These data indicate that RPR 109891 causes rapid and selective sequestration of platelets in the spleen.

Abciximab. An updated review of its use in ischaemic heart disease

Abciximab is a glycoprotein IIb/IIIa receptor antagonist that has proven to be of significant clinical value in improving patient outcome after percutaneous coronary revascularisation. Primarily, the drug inhibits platelet aggregation, but it may also have anticoagulant activity and other beneficial effects, such as inhibiting migration and promoting apoptosis of smooth muscle cells. Large well designed studies have found administration of abciximab (as an adjunct to heparin and aspirin) during percutaneous coronary revascularisation to significantly reduce the incidence of ischaemic complications occurring in the 30 days after the procedure. Significant benefit, particularly on the incidence of myocardial infarction, was still evident after 6 months in 2 of 4 major trials. Abciximab provides particular benefit in patients with unstable angina or myocardial infarction who are undergoing percutaneous coronary revascularisation. The benefits of the drug are additive to those achieved with coronary stenting. Very preliminary data suggest that abciximab may improve coronary blood flow after myocardial infarction and allow reperfusion to be achieved with reduced thrombolytic doses. Caution is required to minimise the risk of bleeding complications with the use of abciximab in combination with heparin and aspirin. Careful patient selection, use of an appropriate heparin regimen, early vascular sheath removal and meticulous femoral artery access site care are recommended. Thrombocytopenia can occur with abciximab treatment, but severe cases are uncommon (< 2% of patients) and can be treated with platelet transfusions. The high acquisition cost of abciximab may be partly or fully offset by the costs averted by the reduced incidence of ischaemic complications and need for urgent and/or repeat revascularisation in high risk patients who receive the drug. However, if bleeding complications occur, this adds to treatment costs. Cost effectiveness analyses generally support the use of abciximab in high risk patients.

CONCLUSIONS

Abciximab can be recommended for the prevention of acute ischaemic events in most patients undergoing percutaneous coronary revascularisation, but careful patient selection and strict adherence to the recommended treatment protocol are required to reduce the risk of bleeding complications and thrombocytopenia. Its use in high risk patients is largely supported by pharmacoeconomic data. Further pharmacoeconomic information is needed to establish the drug as a standard of care for all patient groups. The indications for abciximab are likely to expand as more data on its use in acute coronary syndromes become available.