Inhibition Of Platelet Glycoprotein Research Articles

Treatment of non-ST-elevation myocardial infarction and ST-elevation myocardial infarction in patients with chronic kidney disease.

Renal dysfunction is frequent in patients with non-ST-segment elevation acute coronary syndrome (NSTE-ACS). Chronic kidney disease (CKD) is associated with very poor prognosis and is an independent predictor of early and late mortality and major bleeding in patients with NSTE-ACS. Patients with NSTE-ACS and CKD are still rarely treated according to guidelines. Medical registers reveal that patients with CKD are usually treated with too high doses of antithrombotics, especially anticoagulants and inhibitors of platelet glycoprotein (GP) IIb/IIIa receptors, and therefore they are more prone to bleeding. Drugs which are excreted mainly or exclusively by the kidney should be administered in a reduced dose or discontinued in patients with CKD. These drugs include enoxaparin, fondaparinux, bivalirudin, and small molecule inhibitors of GP IIb/IIIa inhibitors. In long-term treatment of patients after myocardial infarction, anti-platelet therapy, lipid-lowering therapy and β-blockers are used. Chronic kidney disease patients before qualification for coronary interventions should be carefully selected in order to avoid their use in the group of patients who could not benefit from such procedures. This paper presents schemes of non-ST and ST-segment elevation myocardial infarction treatment in CKD patients in accordance with the current recommendations of the European Society of Cardiology (ESC).

An audit of the use and complications of glycoprotein IIb/IIIa inhibitors in percutaneous coronary intervention against national UK standards

Coronary thrombosis is a pivotal event in the pathogenesis of acute coronary syndromes and ischemic complications resulting from coronary intervention. Activation of the platelet glycoprotein (GP) IIb/IIIa receptor is the final common pathway leading to platelet aggregation, coronary thrombus formation, and myocardial ischemia. Inhibitors of platelet GP IIb/IIIa are potent agents to prevent progression to myocardial infarction and death. We prospectively surveyed the indications, frequency, and complications associated with the use of GP IIb/IIIa inhibitors in percutaneous coronary intervention in a tertiary center setting. A total of 170 patients underwent screening over a period of 6 weeks. One hundred four (61%) had coronary intervention, out of which eight (8%) had failed intervention. Glycoprotein IIb/IIIa inhibitors were used in 57 (55%) patients; 47 (45%) did not have any agent periprocedure. Eptifibatide was the most commonly used agent in 35 (33%), followed by abciximab in 19 (18%) and tirofiban in 3 (3%). Out of 57 patients in whom GP IIb/IIIa agents were used, 22 (38%) had visible intracoronary thrombus, 22 (38%) had diffuse disease, 8 (14%) had complex intervention, and 5 (9%) had diabetes. The overall incidence of complications was not increased by the use of GP IIb/IIIa inhibitors; serious complications were rare with the use of GP IIb/IIIa agents; no stroke, thrombocytopenia, gastrointestinal bleed, or death was recorded. The overall use in emergency settings was not associated with increased complications. Bradycardia and vomiting were more common with abciximab group, whereas puncture site pain was commoner in eptifibatide group.

Gli antagonisti del recettore GPIIb/IIIa: farmacologia, clinica ed economia nelle sindromi coronariche acute NSTEMI e nelle rivascolarizzazioni per via percutanea

Inhibition of platelet glycoprotein IIb/IIIa (GP IIb/IIIa) receptor prevents platelet aggregation by controlling its final common pathway, the cross-binding of fibrinogen, bridging across adjacent platelets. Three pharmacological agents capable of inhibiting GP IIb/IIIa are available for use in Italy: abciximab, eptifibatide and tirofiban. In this paper, some relevant studies on the pharmacology of GP IIb/IIIa inhibitors are summarized, as well as the main clinical trials assessing their use in the management of unstable angina (UA) and during percutaneous coronary interventions (PCI). Furthermore, the recommendations on their appropriate use in UA and PCI issued by authoritative scientific societies are presented. Finally, some of the pharmacoeconomic evidence published in the international literature is reviewed and implications in the Italian health care setting are discussed.

Spotlight on Eptifibatide in Percutaneous Coronary Intervention and Acute Coronary Syndromes1

Eptifibatide (Integrilin®) is a selective inhibitor of platelet glycoprotein IIb/IIIa receptors used as adjunctive therapy for patients undergoing percutaneous coronary intervention (PCI) and for patients with acute coronary syndromes (ACS), particularly those requiring PCI. Most economic analyses of eptifibatide have incorporated clinical and healthcare resource use data from either the ESPRIT (Enhanced Suppression of the Platelet IIb/IIIa Receptor with Integrilin® Therapy) study in low- to moderate-risk patients undergoing selective PCI with stent implantation or the PURSUIT (Platelet Glycoprotein Ilb/IIIa in Unstable Angina: Receptor Suppression Using Integrilin® Therapy) trial in patients with ACS. Eptifibatide achieved statistically significant reductions in combined endpoints of death and ischemic complications in both of these large multicenter clinical trials, in which patients were randomized to receive intravenous eptifibatide or placebo as adjunctive therapy to heparin and aspirin (plus a thienopyridine in ESPRIT). In US economic analyses using ESPRIT trial data, approximately 40% and 70% of the acquisition cost of eptifibatide was offset by reduced medical resource consumption during the initial hospitalization period and over a 1-year period, respectively. Eptifibatide was associated with a favorable cost-effectiveness ratio of $US1407 (year 2000 values) per life-year gained (LYG) in a retrospective US cost-effectiveness analysis that incorporated data from the ESPRIT trial and modeled life expectancy using a large cardiovascular database. Several cost-effectiveness analyses used prospectively collected data from the PURSUIT trial and modeled survival projections using similar methods. These analyses, conducted in the US, Canada, and Western Europe, also showed favorable results ($US3761-$US18 774 per LYG; various years of costing). Cost-utility ratios reported in US analyses varied somewhat, but remained <$US20 000 per quality-adjusted life-year gained (1996 values) when clinical efficacy data were derived from the US cohort of PURSUIT. In conclusion, significant clinical benefits have been demonstrated with eptifibatide as adjunctive therapy in patients undergoing selective PCI with stent implantation in the ESPRIT trial and in patients with ACS in the PURSUIT trial. Pharmacoeconomic analyses using data from either ESPRIT or PURSUIT have demonstrated favorable cost-effectiveness ratios for both indications in various countries. ESPRIT-based results from the limited number of available economic analyses are particularly favorable. The cost-effectiveness of eptifibatide in ACS (i.e. PURSUIT-based results) may be further improved by targeting the drug for patients in whom catheterisation and PCI are planned, although further analyses are required to confirm this.

Eptifibatide

Eptifibatide (Integrilin) is a selective inhibitor of platelet glycoprotein (GP) IIb/IIIa receptors used as adjunctive therapy for patients undergoing percutaneous coronary intervention (PCI) and for patients with acute coronary syndromes (ACS), particularly those requiring PCI. Most economic analyses of eptifibatide have incorporated clinical and healthcare resource use data from either the ESPRIT (Enhanced Suppression of the Platelet IIb/IIIa Receptor with Integrilin Therapy) study in low- to moderate-risk patients undergoing selective PCI with stent implantation or the PURSUIT (Platelet Glycoprotein IIb/IIIa in Unstable Angina: Receptor Suppression Using Integrilin Therapy) trial in patients with ACS. Eptifibatide achieved statistically significant reductions in combined endpoints of death and ischaemic complications in both of these large multicentre clinical trials, in which patients were randomised to receive intravenous eptifibatide or placebo as adjunctive therapy to heparin and aspirin (plus a thienopyridine in ESPRIT). In US economic analyses using ESPRIT trial data, approximately 40% and 70% of the acquisition cost of eptifibatide was offset by reduced medical resource consumption during the initial hospitalisation period and over a 1-year period, respectively. Eptifibatide was associated with a favourable cost-effectiveness ratio of $US1407 (year 2000 costs) per life-year gained (LYG) in a retrospective US cost-effectiveness analysis that incorporated data from the ESPRIT trial and modelled life expectancy using a large cardiovascular database.Several cost-effectiveness analyses used prospectively collected data from the PURSUIT trial and modelled survival projections using similar methods. These analyses, conducted in the US, Canada and Western Europe, also showed favourable results ($US3761-$US18 774 per LYG; various years of costing). Cost-utility ratios reported in US analyses varied somewhat, but remained <$US20 000 per quality-adjusted life-year gained (1996 values) when clinical efficacy data were derived from the US cohort of PURSUIT. Significant clinical benefits have been demonstrated with eptifibatide as adjunctive therapy in patients undergoing selective PCI with stent implantation in the ESPRIT trial and in patients with ACS in the PURSUIT trial. Pharmacoeconomic analyses using data from either ESPRIT or PURSUIT have demonstrated favourable cost-effectiveness ratios for both indications in various countries. ESPRIT-based results from the limited number of available economic analyses are particularly favourable. The cost-effectiveness of eptifibatide in ACS (i.e. PURSUIT-based results) may be further improved by targeting the drug for patients in whom catheterisation and PCI are planned, although further analyses are required to confirm this.

The role of platelets in blood coagulation—effects of platelet agonists and GPIIb/IIIa inhibitors studied by free oscillation rheometry

We have studied the contribution of platelets to the coagulation of plasma and the effects of activation or inhibition of platelets on the coagulation process in unanticoagulated fresh whole blood (subsequently termed native blood). For this purpose, we have used a free oscillation rheometer (FOR), the ReoRox4, a new instrument that enables noninvasive viscoelastic measurements of clot formation in plasma and whole blood. Platelets appear essential for the initiation of coagulation if no activating surface is present. We prepared platelet-free plasma by quick centrifugation and filtration of native blood, which did not coagulate if stored in plastic containers at 37 °C but clotted if transferred to glass containers. Addition of platelet agonists, such as collagen or the thrombin receptor agonist peptide, SFLLRN, significantly accelerated the clotting of native blood and also changed the rheometer curve appearance, accelerating both onset and completion of clot formation (i.e. fibrin gel formation). Inhibition of platelet glycoprotein (GP) IIb/IIIa with the peptide-derived compound MK-852 or the antibody-derived abciximab (Reopro) prevented clot retraction and prolonged the clotting time with SFLLRN. In collagen-stimulated samples, MK-852 accelerated clotting but delayed completion of clotting while abciximab prolonged both clotting time and completion of clotting. To our knowledge, this is the first report showing that activation of platelets in native whole blood shortens the coagulation time ex vivo. It also describes a new instrument that enables studies of the viscoelastic properties of a forming whole blood clot.

The interaction between components of the fibrinolytic system and GPIb/V/IX of platelets thrombus formation in mice

The interaction of fibrinolytic components with GPIb/V/IX of platelets on thrombus formation, was investigated in mice deficient in tissue type (tPA-/-), urokinase type plasminogen activator (uPA-/-) or plasminogen activator inhibitor-1 (PAI-1-/-) and in their wild type control (tPA+/+, uPA+/+, PAI-1+/+). A thrombus was induced in the murine carotid artery using a photochemical reaction. The times to occlusion after the initiation of endothelial injury in all wild type mice was within 12 min, and no significant changes in occlusion delay were observed in uPA-/- and tPA-/- mice compared to wild type mice, whereas that of PAI-1 mice were significantly prolonged (16.9+/-2.9 min, P<0.05). When high molecular weight aurintricarboxylic acid (ATA), an inhibitor of platelet glycoprotein Ib/V/IX, was administered, the time to occlusion was prolonged in a dose-dependent manner in all types of mice. However, when this compound was injected in tPA-/- mice, the most significant changes were observed: i.e. the estimated ED(50) was 20.2 times higher than that in tPA+/+ mice, but the estimated ED(50) in uPA-/- mice was not changed as compared with that of wild type mice. On the other hand, when ATA was injected in PAI-1-/- mice, the estimated ED(50) was significantly decreased (P<0.05). Platelet aggregation induced by botrocetin was not significantly different among all types of mice. The bleeding time was prolonged in a dose dependent-manner when ATA was injected in all types of mice. In conclusion, the antithrombotic effect of inhibition of platelet GPIb/V/IX is severely affected by the absence or presence of tPA-production on thrombus formation and the inhibition of PAI-1 could enhance this antithrombotic effect.

Selected Articles: Inhibition of platelet aggregation in unstable angina

Article chosen The PURSUIT investigators. Inhibition of platelet glycoprotein IIb/IIIa with eptifibatide in patients with acute coronary syndromes. N Engl J Med 1998;339:436-43. Objective To determine if early platelet inhibition with eptifibatide will provide incremental benefit beyond that of heparin and ASA in preventing adverse outcomes for patients with acute coronary syndromes who do not have persistent STsegment elevation.

Pharmacological analysis of integrin function: inhibition of vascular stenosis and identification of a novel antiplatelet substance

The long-lasting success of PTCA, a common treatment for patients with coronary artery disease, is hampered by acute reocclusion due to thrombus and by late restenosis due to smooth muscle cell (SMC) migration and proliferation. Recently potent antiplatelet agents such as inhibitors of platelet glycoprotein (GP) IIb/IIIa (alpha IIb/beta 3) have become available and are highly effective in humans. We investigated the inhibitory effects of these compounds on vascular stenosis. Administration of an RGD-containing peptide (non-selective alpha IIb/beta 3 antagonist) results in reduction of neointima, but selective alpha IIb/beta 3 antagonists have no effect. This effect is due both to an early event, which could be due to the inhibition of secretion of PDGF from activated platelets with blocked alpha IIb/beta 3, and to a late event, by interference with SMC alpha v/beta 3. Moreover, platelet adhesion via GPIb/V/IX is a trigger for thrombus formation. Inhibition of platelet adhesion results in the prevention of thrombus formation and the suppression of neointima. However, this effect was supported by the reduction of SMC proliferation. Therefore, these dual inhibitions markedly reduced vascular stenosis. Finally some low molecular mass heat shock proteins (HSPs) appear to act as molecular chaperones, but their physiological roles have not been fully elucidated. We have investigated the physiological role of p20, a kind of HSP, on platelet function. p20 inhibited platelet aggregation. Our findings may provide the basis for a novel defensive system against thrombus formation.

Comparison of the Antithrombotic Effects and Bleeding Risk of Fractionated Aurin Tricarboxylic Acid and the GPIIb/IIIa Antagonist GR144053 in a Hamster Model of Stenosis

The present study compared the antithrombotic properties of fractionated aurin tricarboxylic acid (ATA), an inhibitor of platelet glycoprotein (GP) Ib, and GR144053, a GPIIb/IIIa antagonist, in a hamster model of stenosis. Endothelial cell injury in the hamster carotid artery was achieved by a 2F modified catheter. Arterial blood flow in the control groups was interrupted 5.4±0.9 minutes after the injury. When ATA (0.01, 0.03, 0.1, 0.3, and 1.0 mg/kg per hour) or GR144053 (0.1, 0.3, and 1.0 mg/kg per hour) were continuously infused intravenously, the time elapse before the vessel completely occluded was prolonged in a dose-dependent manner. However, all arteries in the ATA-treated groups ultimately occluded during the observation period even if the aggregation of platelets ex vivo and induced by botrocetin was completely inhibited. When either ATA (0.1 mg/kg per hour) or GR144053 (0.3 mg/kg per hour) were infused via an implanted osmotic pump together with tissue-type plasminogen activator (tPA), late patency of the reperfused artery was improved compared to that of arteries treated with TPA alone. However, the cyclic reflow pattern after reperfusion on days 0 and 1 was not reduced by the ATA treatment. The bleeding time was significantly prolonged when either ATA or GT144053 was coadministered with tPA. The treatment with ATA showed an especially marked prolongation of the bleeding time. In conclusion, both inhibition of platelet activation by ATA or GR144053 prevent arterial thrombosis and enhance the thrombolytic effect of tPA, but GR144053 was more protective in its antithrombotic effect and more effective during thrombolytic therapy than ATA.

AL–2 - Pharmacological analysis of integrin function: Inhibition of vascular stenosis and identification of a novel antiplatelet substance.

The long-lasting success of PTCA, a common treatment for patients with coronary artery disease, is hampered by acute reocclusion due to thrombus and by late restenosis due to smooth muscle cell (SMC) migration and proliferation. Recently potent antiplatelet agents such as inhibitors of platelet glycoprotein (GP) IIb/IIIa (alpha IIb/beta 3) have become available and are highly effective in humans. We investigated the inhibitory effects of these compounds on vascular stenosis. Administration of an RGD-containing peptide (non-selective alpha IIb/beta 3 antagonist) results in reduction of neointima, but selective alpha IIb/beta 3 antagonists have no effect. This effect is due both to an early event, which could be due to the inhibition of secretion of PDGF from activated platelets with blocked alpha IIb/beta 3, and to a late event, by interference with SMC alpha v/beta 3. Moreover, platelet adhesion via GPIb/V/IX is a trigger for thrombus formation. Inhibition of platelet adhesion results in the prevention of thrombus formation and the suppression of neointima. However, this effect was supported by the reduction of SMC proliferation. Therefore, these dual inhibitions markedly reduced vascular stenosis. Finally some low molecular mass heat shock proteins (HSPs) appear to act as molecular chaperones, but their physiological roles have not been fully elucidated. We have investigated the physiological role of p20, a kind of HSP, on platelet function. p20 inhibited platelet aggregation. Our findings may provide the basis for a novel defensive system against thrombus formation.

Eptifibatide reduced deaths and nonfatal myocardial infarction in acute coronary syndromes

Source Citation The PURSUIT Trial Investigators. Inhibition of platelet glycoprotein IIb/IIIa with eptifibatide in patients with acute coronary syndromes. N Engl J Med. 1998 Aug 13;339:436-43.

Preferential Benefit of Platelet Glycoprotein IIb/IIIa Receptor Blockade: Specific Considerations by Device and Disease State

Several patient subgroups appear to benefit preferentially from inhibition of platelet glycoprotein (GP) IIb/IIIa receptors. In clinical trials the GP IIb/IIIa blocker abciximab (ReoPro; Lilly) proved both safe and effective in improving outcomes after coronary interventions. Endpoints of death, myocardial infarction (MI), and need for urgent intervention were significantly decreased in a randomized placebo-controlled trial of patients treated with abciximab in conjunction with either low-dose or standard-dose weight-adjusted heparin during elective percutaneous coronary revascularization. In addition, studies have shown that patients undergoing unplanned stent deployment or ablative technologies benefit from GP IIb/IIIa blockade. Patients undergoing saphenous vein graft intervention also derive specific benefits. These agents—specifically abciximab, eptifibatide (INTEGRILIN; Cor/Schering), and tirofiban—have also benefited patients with the acute coronary syndromes (e.g., unstable angina) by decreasing ischemic events.

Boundary layer drug delivery using a helical catheter

Background: A catheter-based approach for local endovascular drug delivery has been developed. The catheter is deployed percutaneously, while the end of the catheter is in the form of a helix that is placed just proximal to the vascular site to be treated. The helices are in contact with the vessel wall. A number of small holes is drilled in the coils of the catheter through which drug is infused, so that the infused drug remains within the blood fluid `boundary layer' adjacent to the vessel wall. This approach is expected to be highly efficient for administration of antithrombotic and antiproliferative agents that target processes leading to vascular occlusion, heart attacks, and strokes. Methods: The helical catheter was qualitatively evaluated using optical dye density measurements of Evans blue dye infused using an in vitro steady flow system under a physiologic range of conditions. To further demonstrate the efficiency of the technique, its capacity to inhibit thrombosis was evaluated in a baboon thrombosis model. The catheter was inserted into a femoral arteriovenous shunt (blood flow rate=100 ml/min) and placed proximal to a segment of highly thrombogenic Dacron vascular graft (4.0 mm i.d.). Integrelin (an inhibitor of platelet glycoprotein IIb/IIIa; doses: 0.25–1.0 μg/min) and hirudin (an antithrombin; doses: 10–100 μg/min) were used to inhibit thrombus formation. Results: Experimental flow visualization studies demonstrated that high concentrations of the infused Evans blue dye were retained near the vessel wall. In the animal experiments, platelet deposition on the Dacron graft surface was reduced by 82–97% (Integrelin) and 68–92% (hirudin) over 1–2 h of blood exposure. The local antithrombotic effects produced were found to be 200-fold and 30-fold more efficient than systemic administration of the same agents. Conclusions: Local drug infusion using the helical catheter approach can achieve high drug concentration levels at target sites, may avoid systemic effects, and can reduce cost of therapy by reducing total drug requirements.

Effect of platelet glycoprotein IIb/IIIa receptor inhibition on distal embolization during percutaneous revascularization of aortocoronary saphenous vein grafts

Percutaneous treatment of narrowed aortocoronary saphenous vein graft disease represents a viable option for patients with recurrent angina following coronary artery bypass grafting. Present strategies are limited by high rates of distal embolization, non-Q-wave acute myocardial infarction (AMI), and restenosis. Because these complications may be mediated by platelets, inhibition of platelet glycoprotein IIb/IIIa receptor, the final common pathway for aggregation, may improve clinical outcomes. In the Evaluation of IIb/IIIa platelet receptor antagonist 7E3 in Preventing Ischemic Complications (EPIC) trial, 2,099 patients undergoing high-risk percutaneous coronary revascularization were randomized to receive abciximab bolus and infusion, abciximab bolus followed by placebo infusion or placebo. A total of 101 patients were treated for narrowing of saphenous vein grafts, 38 in the bolus and infusion group, 34 in the bolus group and 29 in the placebo group. Clinical end points included all-cause mortality, nonfatal AMI and need for repeat revascularization at 30 days. Compared with placebo, bolus and infusion therapy resulted in a significant reduction in distal embolization (2% vs 18%, p = 0.017) and a trend towards reduction in early large non-Q-wave AMI (2% vs 12%, p = 0.165). The occurrence of a 30-day composite end point was similar among the 3 treatment groups. At 6 months, there was also no difference in the composite end point. These results suggest that adjunctive therapy with abciximab during percutaneous treatment of narrowed saphenous vein grafts reduces the occurrence of distal embolization, and possibly non-Q-wave AMI.

Activation of blood coagulation by plaque rupture: Mechanisms and prevention

Inhibition of thrombosis is proving to be an important treatment goal in many clinical situations, including coronary thrombolysis, angioplasty, and unstable angina. Heparin is a potent inhibitor of thrombin and thrombin generation, but its ability to accelerate thrombolysis, prevent acute reocclusion after vascular injury in angioplasty, and prevent myocardial infarction in unstable angina is relatively limited, possibly because clot-bound thrombin plays an important role in these clinical situations. Thus, when thrombin binds to fibrin, it remains enzymatically active and relatively impervious to inactivation by heparin or other fluid-phase inhibitors. However, direct thrombin inhibitors—such as d-Phe- l-Pro- l-Arg-CH 2CI (PPACK), hirudin, hirugen, and hirulog—inhibit free and clot-bound thrombin with equal efficacy, presumably because their sites of interaction are not masked when thrombin binds to fibrin. Advanced clinical trials suggest that the direct thrombin inhibitors and 7E3, an inhibitor of platelet glycoprotein IIb/IIIa, will soon be incorporated into the armamentarium against arterial thrombosis.

Aurintricarboxylic Acid Reduces Platelet Deposition in Stenosed and Endothelially Injured Rabbit Carotid Arteries more Effectively than other Antiplatelet Interventions

In the present study we tested the effects of different antithrombotic interventions on platelet deposition in experimentally-stenotic rabbit carotid arteries with endothelial injury. Platelet deposition, quantitated by labeling autologous platelets with 111In-oxine, was significantly reduced compared to control animals by all interventions tested, i.e., R 68070, a drug with thromboxane A2 synthase and receptor blocking properties, BN 52021, a PAF receptor antagonist, aurintricarboxylic acid (ATA), an inhibitor of platelet glycoprotein (Gp) Ib/von Willebrand factor (vWf) interaction, AZ-1, a monoclonal antibody against rabbit GP IIb/IIIa, the platelet receptor for fibrinogen, and AP-1, a monoclonal antibody against rabbit tissue factor. ATA was significantly more effective than all the other interventions in reducing platelet deposition in the stenotic vessels. We conclude that inhibition of Gp Ib/vWf interaction may be a more suitable target for antithrombotic therapy under conditions of high shear stress, like those produced in this model.