Pharmacodynamic and clinical trials of glycoprotein IIb/IIIa inhibitors and potential relationship of results to dosing

Glycoprotein IIb/IIIa inhibitors have become the standard of care for patients undergoing percutaneous coronary intervention (PCI) and for those presenting with non-ST-segment elevation myocardial infarction (NSTE-ACS). Clinical effects of GP IIb/IIIa inhibitors in PCI and NSTE-ACS strongly correlate with potency, consistency, and durability of platelet aggregation inhibition. Under standardized conditions [light transmission aggregometry (LTA), 20 micromol adenosine diphosphate (ADP) as an agonist, and D-phenylalanyl-L-propyl-L-arginine chloromethyl ketone (PPACK) as an anticoagulant], we demand consistent platelet aggregation inhibition >80% during the time of PCI (initial balloon inflation), and during the entire duration of therapy in NSTE-ACS. The benefit of abciximab (bolus 0.25 mg/kg plus infusion 10 microg/kg/min) correlates with >80% inhibition of platelet aggregation during the intervention (PCI) and immediately thereafter (<6 hours). The absence of a benefit with abciximab in NSTE-ACS is most likely due to <80% inhibition during the major part of the infusion period (>6 hours). Tirofiban does not achieve >80% inhibition at the time of PCI at a dose of 10 microg/kg bolus plus 0.15 microg/kg/min infusion, and at a dose of 0.4 lg/kg/min loading infusion for 30 minutes plus 0.1 microg/kg/min maintenance infusion, the target value is only reached after 18 h. Eptifibatide (double-bolus 180 microg/kg 10 min apart, followed immediately by a 2.0 microg/kg/min infusion) provided an instant, consistent, and durable antiplatelet effect for the entire duration of infusion, and a significant clinical benefit in both PCI (non-ACS patients) and medically managed NSTE-ACS patients.     

The role of risk stratification in the decision to provide upstream versus selective glycoprotein IIb/IIIa inhibitors for acute coronary syndromes: a cost-effectiveness analysis.

OBJECTIVES: We endeavored to determine under what conditions a strategy of upstream use of small molecule platelet glycoprotein (GP) IIb/IIIa inhibitors for all acute coronary syndromes (ACS) patients is cost effective compared to that of selective use of abciximab in only those patients requiring percutaneous coronary intervention (PCI). BACKGROUND: Small molecule GP IIb/IIIa inhibitors have shown benefit in ACS, but abciximab, the more expensive GP IIb/IIIa inhibitor, may be more effective during PCI. However, abciximab does not have proven efficacy in medical management. No prior study has attempted to balance these competing benefits. METHODS: A decision analysis was performed to examine two strategies: 1) treat all ACS patients upstream with a small molecule GP IIb/IIIa inhibitor and continue through medical management and PCI, if performed; or 2) wait, and selectively use abciximab only in patients who ultimately undergo PCI. Applicable randomized controlled trial data were used for the principal analysis. RESULTS: The strategy of upstream use of a small molecule GP IIb/IIIa inhibitor was superior to selective use, and economically acceptable, with a cost-effectiveness ratio of 18,000 dollars per year of life gained. The superiority of the upstream use strategy persisted over the majority of sensitivity analyses. When stratified by risk according to Thrombolysis in Myocardial Infarction risk score, a strategy of upstream use was only cost effective in those patients with moderate or high risk. CONCLUSIONS: Upstream use of small molecule GP IIb/IIIa inhibition in ACS patients with moderate or high risk for cardiovascular events is a cost-effective approach that should be considered in this subset of patients.     

Time course, magnitude, and consistency of platelet inhibition by abciximab, tirofiban, or eptifibatide in patients with unstable angina pectoris undergoing percutaneous coronary intervention.

Adjunctive platelet glycoprotein IIb/IIIa blockade during percutaneous coronary intervention (PCI) reduces platelet-mediated adverse ischemic outcomes. Although abciximab, eptifibatide, and tirofiban have received U.S. Food and Drug Administration approval for use, these agents differ in their pharmacodynamic profiles. Each of these agents has been compared in randomized trials with placebo for patients undergoing PCI, but no randomized comparative studies of these agents have been performed. We compared ex vivo platelet function by both standard light transmission aggregometry and rapid platelet function assay during and after administration of abciximab, eptifibatide, or tirofiban in approved dose regimens on a randomized basis at the time of PCI in patients with unstable angina pectoris. A reduced intensity of platelet inhibition by light transmission aggregometry was observed for tirofiban compared with either eptifibatide or abciximab. In addition, the 30-minute bolus strategy used for tirofiban was associated with delayed onset of maximal platelet inhibition relative to the initiation of bolus infusion. Whether the trends in platelet function observed in this study will be translated into differences in clinical outcomes awaits definition by larger scale randomized clinical trials comparing these platelet glycoprotein IIb/IIIa inhibitors.     

Bivalirudin in PCI: an overview of the REPLACE-2 trial

The Randomized Evaluation in PCI Linking Angiomax to Reduced Clinical Events (REPLACE)-2 trial is one of the largest acute randomized controlled trials evaluating the efficacy of two anticoagulant strategies during contemporary urgent or elective percutaneous coronary intervention (PCI). The direct thrombin inhibitor, bivalirudin, with provisional use of glycoprotein IIb/IIIa (GP IIb/IIIa) inhibitor was compared to low-dose unfractionated heparin (UFH) plus planned GP IIb/IIIa inhibitor. At 30-day follow-up, the primary quadruple composite endpoint (death, myocardial infarction (MI), urgent repeat revascularization, or in-hospital major bleeding) occurred in 9.2% of patients in the bivalirudin group versus 10.0% of patients in the UFH plus GP IIb/IIIa inhibitor group. The secondary triple composite endpoint (death, MI, urgent repeat revascularization) occurred in 7.6% of patients in the bivalirudin group compared with 7.1% of patients in the UFH plus GP IIb/IIIa inhibitor group. Both endpoints met formal statistical criteria for noninferiority to UFH plus GP IIb/IIIa inhibitor. By imputed comparison from historic GP IIb/IIIa trials between bivalirudin versus UFH alone, REPLACE-2 demonstrated that bivalirudin was superior to UFH alone with respect to the quadruple and triple composite endpoints. Furthermore, bivalirudin plus provisional GP IIb/IIIa blockade was associated with a significant reduction in in-hospital bleeding (2.4% vs. 4.1%; p < 0.001). At 6 months' follow-up, there was no significant difference in rates of death, MI, or revascularization between the two groups. Furthermore, there was no evidence that the early, nonsignificant 0.5% excess non-Q-wave MI in the bivalirudin group translated into later mortality. There was a trend toward decreased mortality at 6 months in the bivalirudin arm (0.95% vs. 1.35%; p = 0.148). The relative efficacy of bivalirudin versus UFH plus GP IIb/IIIa inhibitor was similar in several high-risk subgroups, including patients with diabetes mellitus or prior MI, women, the elderly (age > 65 years), and patients undergoing PCI of bypass grafts. Bivalirudin represents an exciting alternative to UFH plus GP IIb/IIIa inhibitor in patients undergoing urgent and elective PCI with similar suppression of ischemic events, fewer bleeding complications, and the potential for greater cost savings and ease of administration.     

Achieved platelet aggregation inhibition after different antiplatelet regimens during percutaneous coronary intervention for ST-segment elevation myocardial infarction

OBJECTIVES: To evaluate the extent of platelet aggregation inhibition in patients with ST-segment elevation myocardial infarction (STEMI) undergoing percutaneous coronary intervention (PCI), treated with different antiplatelet agents and dosages. BACKGROUND: The extent of platelet aggregation inhibition is an independent predictor of major cardiac events after elective PCI. In STEMI patients undergoing PCI, routine dose of antiplatelet agents may be associated with less effective platelet aggregation inhibition. METHODS: Patients were treated with clopidogrel before angiography and randomized to abciximab, tirofiban, high-dose tirofiban, or no glycoprotein (GP) IIb/IIIa inhibitor; GP IIb/IIIa inhibitor bolus, followed by maintenance infusion, was administered after angiography, but before PCI. Platelet aggregation inhibition was assessed before angiography, immediately after PCI, and 1 and 6 h afterwards. RESULTS: The total study population consisted of 112 patients. Platelet aggregation inhibition was variable for individuals and suboptimal for all agents, particularly in the periprocedural period. Only with high-dose tirofiban, mean periprocedural platelet aggregation inhibition exceeded 80%. Angiographic parameters after PCI were not different between the groups. No relationship was found between the level of platelet aggregation and parameters of PCI success (Thrombolysis In Myocardial Infarction frame count and myocardial blush grade), after combining the data from all four groups studied. CONCLUSIONS: Platelet aggregation inhibition in STEMI patients undergoing PCI, treated with antiplatelet agents, is variable and suboptimal for all agents and dosages studied. Only with high-dose tirofiban, mean periprocedural platelet aggregation inhibition exceeded 80%. However, no relationship of platelet aggregation inhibition and angiographic outcome was found in this patient cohort.     

Pharmacodynamic profile of short-term readministration of abciximab in healthy subjects

Objective The purpose of the study was to establish a rebolus regimen for abciximab that restores pharmacologic glycoprotein (GP) IIb/IIIa receptor blockade within a short time frame (up to 48 hours) after completion of an initial treatment. Methods and Results The study was a single-center, nonrandomized, open-label dose escalation trial in healthy volunteers (n = 30). Each subject received a 0.25 mg/kg bolus and a 0.125 μg/kg per minute infusion of abciximab, followed by incremental bolus doses of the agent at 15-minute intervals up to 48 hours (10 per group) after completion of the infusion, (maximal cumulative rebolus dose of 0.25 mg/kg). Pharmacodynamic measurements (GP IIb/IIIa receptor blockade, turbidimetric and whole blood platelet aggregation with use of a rapid platelet function assay [RPFA]) were obtained at periodic intervals during and after administration of the abciximab bolus and infusion. At the time of the first rebolus, pharmacodynamic measurements were attained immediately before administration of each rebolus and 15 minutes after the last rebolus dose. In subjects who received reboluses 12 hours after infusion, a cumulative dose of 0.05 mg/kg restored >80% blockade of GP IIb/IIIa receptors and >80% inhibition of turbidimetric (5 and 20 μmol/L adenosine diphosphate) and RPFA aggregation in 10 of 10 subjects. At 24 hours after treatment, a cumulative abciximab bolus dose of 0.1 mg/kg restored >80% blockade of all 4 pharmacodynamic measurements in 10 of 10 subjects. At 48 hours after treatment, a cumulative bolus dose of 0.15 mg/kg restored >80% blockade of all 4 pharmacodynamic measurements in 10 of 10 subjects. Conclusions A fraction of the bolus of abciximab restored pharmacologic (>80%) GP IIb/IIIa receptor blockade when readministered at various postinfusion time points. These observations suggest that in the setting where acute readministration of abciximab is required less than a full bolus dose of the agent is warranted. (Am Heart J 2002;143:87-94.)     

Platelet glycoprotein IIb/IIIa inhibitor use during percutaneous coronary intervention: IIb or Not IIb,what is the question?

Over the past decade, numerous placebo-controlled randomized clinical trials have documented robust clinical benefits of intravenous platelet glycoprotein (GP) IIb/IIIa inhibitors in patients undergoing percutaneous coronary intervention (PCI). This evidence has led to U.S. Food and Drug Administration approval and indication for use of two GP IIb/IIIa inhibitors at the time of PCI, namely, the chimeric monoclonal antibody fragment abciximab (ReoPro, Centocor, Inc. and Eli Lilly & Company) and the cyclic heptapeptide small molecule eptifibatide (Integrilin, COR Therapeutics and Key Pharmaceuticals). Currently, another small molecule GP IIb/IIIa inhibitor, tirofiban (Aggrastat, Merck & Company), which (similar to eptifibatide) is approved for the medical therapy of patients with non-ST segment elevation acute coronary syndromes (ACS), has not received indication for use in the PCI setting. Although the clinical benefits of both abciximab and eptifibatide administered at the time of PCI have been proven in randomized clinical trials, only abciximab has demonstrated a late survival advantage in patients following PCI. Evidence in support of the presence, magnitude and possible mechanisms for abciximab survival advantage is herein reviewed.     

Meta-analysis of survival with platelet glycoprotein IIb/IIIa antagonists for percutaneous coronary interventions

We performed a cumulative meta-analysis of available studies to evaluate the effect of intravenous platelet glycoprotein (GP) IIb/IIIa antagonists on survival at 30 days and 6 months after percutaneous coronary intervention (PCI). Compounds that block the GP IIb/IIIa receptor substantially reduce myocardial infarctions (MIs) and repeat revascularization. We included 12 trials, which enrolled 20,186 patients in all, in the analysis. Overall, 30-day mortality was significantly reduced with GP IIb/IIIa inhibition (odds ratio 0.73, 95% confidence interval 0.55 to 0.96, p = 0.024). Although 10 of the 12 trials showed a beneficial effect of GP IIb/IIIa inhibitor treatment on mortality, no individual trial detected a statistically significant mortality benefit. The 30-day mortality benefit became significant at the p <0.05 level with addition of the ADMIRAL trial and was further enhanced by the CADILLAC trial. No significant heterogeneity was detected in the collection of trials. At 6 months, the odds ratio was 0.84 (95% confidence interval 0.69 to 1.03, p = 0.087). This survival benefit amounts to preventing approximately 1 of every 3 deaths that occur within 30 days after PCI, saving 2.8 lives/1,000 patients treated (number needed to treat, 357). Thus, patients who undergo PCI can expect significantly lower 30-day mortality, in addition to known reductions in nonfatal MI and repeat procedures, with GP IIb/IIa inhibition. There also is increasing evidence that mortality reductions are preserved at 6 months.     

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.     

Triple antiplatelet therapy during percutaneous coronary intervention is associated with improved outcomes including one-year survival: results from the Do Tirofiban and ReoProGive Similar Efficacy Outcome Trial (TARGET)

OBJECTIVE: We sought to examine if clopidogrel treatment initiated before coronary stenting improved clinical outcomes among patients receiving aspirin and a glycoprotein (GP) IIb/IIIa inhibitor. BACKGROUND: Antiplatelet therapy plays a pivotal role in contemporary percutaneous coronary interventions (PCI). METHODS: Outcomes among 4,809 patients randomized to tirofiban or abciximab during PCI with stent placement were compared according to whether they received 300 mg of clopidogrel before PCI (93.1%) versus immediately after the procedure. RESULTS: The 30-day primary composite end point (death, myocardial infarction [MI], or urgent target vessel revascularization [TVR]) was lower among clopidogrel-pretreated patients (6.6% vs. 10.4%, p = 0.009), mainly because of reduction of MI (6.0% vs. 9.5%, p = 0.012). The benefit of clopidogrel pretreatment was sustained at six months (death, MI, any TVR: 14.6% vs. 19.8%, HR = 0.71, p = 0.010), and this was due mainly to lowering of death and MI (7.8% vs. 13.0%, p = 0.001). At one year, clopidogrel pretreatment was associated with a lower mortality rate (1.7% vs. 3.6%, p = 0.011). Because clopidogrel pretreatment was not randomized, multivariable and propensity analyses were performed. After adjusting for baseline heterogeneity, clopidogrel pretreatment was an independent predictor for death or MI at 30 days (HR = 0.63, p = 0.012) and at six months (HR = 0.61, p = 0.003), and survival at one year (HR = 0.53, p = 0.044). No excess in 30-day bleeding events was noted with clopidogrel pretreatment. CONCLUSIONS: Among patients undergoing coronary stent placement with aspirin and a GP IIb/IIIa inhibitor, clopidogrel pretreatment is associated with a reduction of death and MI irrespective of the type of GP IIb/IIIa inhibitor used.     

Pharmacodynamics,safety, and clinical effects of a novel glycoprotein IIb/IIIa antagonist framon during high risk coronary angioplasty

Preparation framon [F(ab')2 fragments of the anti-glycoprotein (GP) IIb/IIIa monoclonal antibody (FRaMon)] blocks fibrinogen binding to GP IIb/IIIa and platelet aggregation. Dynamics of platelet aggregation inhibition, safety, and clinical effects of framon were studied in high-risk coronary angioplasty. Twenty seven patients underwent angioplasty with framon, 29 - with abciximab and 28 - with no GP IIb/IIIa antagonists. Framon at 0.2 mg/kg (n=16) and 0.25 mg/kg (n=11) bolus administration inhibited platelet aggregation induced by 20 mcM ADP by more than 90%, 80%, 60% and 30% in comparison with the predrug level 1, 12, 24 and 72 h after injection, respectively. Almost the same dynamics of aggregation inhibition was observed upon abciximab administration at 0.25 mg/kg bolus + 0.125 mcg/kg/min infusion for 12 h. No signs of individual intolerance and side effects including allergic reactions and bleedings were detected in patients treated with framon. Slight decrease of platelet count (15-20%) was observed on the first day after framon administration. Antibodies against framon were detected in 1 out of 22 tested patients. Free (nonbound to platelets) framon was completely removed from the circulation 12 h after injection. The number of endpoints (death, myocardial infarction and indications for repeat revascularization) within 1 year after angioplasty was approximately the same in the groups with framon and abciximab - 7 of 25 (28%) and 7 of 28 (25%), respectively, and more than 1.5 fold higher in the group without GP IIb/IIIa blockers - 12 of 27 (44,4%).     

Safety of glycoprotein IIb/IIIa inhibitors in urgent or emergency coronary artery bypass graft surgery

Approximately 2% to 4% of patients undergo urgent or emergency coronary artery bypass grafting (CABG) for complications of percutaneous coronary intervention (PCI) after treatment with glycoprotein (GP) IIb/IIIa inhibitors. The pharmacokinetic and pharmacodynamic properties of GP IIb/IIIa inhibitors play a large role in determining the safety of their use in the setting of urgent or emergency CABG procedures. Emergency or urgent CABG after treatment with the GP IIb/IIIa inhibitor, abciximab, may be associated with increased risk of hemorrhage and the requirement of platelet transfusions if surgery is performed within 12 h of abciximab discontinuation. Eptifibatide is associated with a similar risk compared with placebo, even when surgery is performed within 2 h of eptifibatide cessation. Limited data for tirofiban show that bleeding is not increased when compared with acetylsalicylic acid or heparin. Eptifibatide and tirofiban appear to have favourable safety profiles compared with abciximab in the setting of emergency or urgent CABG after failed PCI.     

Use of ICHOR-platelet works to assess platelet function in patients treated with GP IIb/IIIa inhibitors.

Platelet glycoprotein GP IIb/IIIa inhibitors have been recently approved for use in treating patients with acute coronary syndromes and those undergoing PCI. The purpose of this study was to assess the feasibility of using a new device, the ICHOR platelet works, to detect platelet inhibition in patients undergoing PCI and treated with abciximab or tirofiban. The study was conducted at Baylor College of Medicine, Houston, Texas. Thirty patients undergoing PCI and treated with abciximab (n = 10) or tirofiban (n = 20) are included. Blood samples were obtained before, at 30 min, at 4 hr, and at 12 hr after starting the GP IIb/IIIa inhibitors and 2 hr after discontinuation. Baseline studies revealed > 95% platelet aggregability in all patients after exposure to ADP (20 microM). After starting tirofiban, 82%, 83%, and 82% of platelets were inhibited at 30 min, 4 hr, and 12 hr. Platelet inhibition decreased to 43% 2 hr after discontinuation of tirofiban. Similarly, ICHOR platelet works detected 91%, 92%, and 85% platelet inhibition at 30 min, 4 hr, and 12 hr after starting abciximab, respectively. Platelet inhibition decreased to 73% 2 hr after discontinuation. The ICHOR platelet works is a promising, simple, and rapid bedside method that may have clinical utility in assessing platelet inhibition in patients treated with GP IIb/IIIa inhibitors. Cathet Cardiovasc Intervent 2001;53:346-351.     

Combination Enoxaparin and Abciximab During Percutaneous Coronary Intervention: A New Standard of Care?

Evidence from randomized trials supports the administration of platelet glycoprotein (GP) IIb/IIIa blockade both to patients undergoing percutaneous coronary intervention (PCI) and those presenting with non-ST elevation acute coronary syndromes (ACSs). Similarly, the low molecular weight heparin (LMWH), enoxaparin, has demonstrated superior efficacy when compared with unfractionated heparin (UFH) in the treatment of patients with non-ST elevation ACS. Algorithms for seamless integration of pharmacotherpy through the course of hospitalization for patients who present with ACS and who require PCI will likely combine therapy with enoxaparin and platelet GP IIb/IIIa blockade (abciximab). Our preliminary experience with combination enoxaparin and abciximab as adjunctive pharmacotherapy for PCI suggests that this strategy is safe and effective and may offer advantages over a conventional strategy, which employs UFH.     

Drip and Ship: A New Strategy for the Treatment of Acute Coronary Syndromes

Glycoprotein (GP) IIb/IIIa inhibitors block the final common pathway of platelet aggregation by preventing fibrinogen from binding to the GP IIb/IIIa platelet receptor. In patients with unstable angina (UA) or a non–Q wave myocardial infarction (NQWMI), including those with UA refractory to medical therapy, these agents decrease the risk of death, myocardial infarction (MI), and recurrent ischemia. Most patients with acute coronary syndromes are managed in hospitals without on-site angioplasty capabilities and often require transfer for an interventional procedure. We propose that GP IIb/IIIa inhibitors can be safely initiated at the referring hospital. We studied 20 patients with UA/NQWMI in whom therapy with a GP IIb/IIIa inhibitor, in addition to standard medical therapy, was initiated prior to transfer for an urgent percutaneous coronary intervention (PCI) (drip and ship). The primary end point was a composite of death, MI, and recurrent ischemia at 30 days. Twelve patients were treated with abciximab, 5 patients were treated with tirofiban, and 3 patients initially treated with tirofiban were converted to abciximab. Procedural success occurred in 33 out of 36 (92%) lesions and 18 out of 20 (90%) patients. At 30 days, 4 out of 20 (20%) patients had recurrent ischemia. The PTCA sites were widely patent in the 3 patients who underwent repeat angiography. The fourth patient had an unsuccessful PCI and was referred for coronary artery bypass surgery. There were no MIs or deaths. Patients who require transfer for an urgent PCI can be managed safely and efficaciously by initiating a GP IIb/IIIa inhibitor, in addition to standard medical therapy, prior to transfer.     

Intravenous glycoprotein IIb/IIIa receptor antagonists reduce mortality after percutaneous coronary interventions

OBJECTIVES: We sought to evaluate the impact of intravenous antagonists of the platelet IIb/IIIa receptor on the survival of patients undergoing percutaneous coronary interventions (PCIs). BACKGROUND: Several trials have shown that intravenous antagonists of the platelet glycoprotein (GP) IIb/IIIa receptor reduce the incidence of myocardial infarction (MI) and composite cardiac outcomes (death, MI, or revascularization) in patients undergoing PCI. However, individual studies have not had adequate power to examine differences in mortality. METHODS: We performed a meta-analysis of 19 randomized, placebo-controlled trials (20 comparisons, n = 20,137). Death was the primary outcome. Secondary outcomes included MI, composite cardiac outcomes, and major bleeding. RESULTS: Mortality was significantly reduced at 30 days (risk ratio [RR] 0.69 [95% confidence interval [CI] 0.53 to 0.90]), at six months (RR 0.79 [95% CI 0.64 to 0.97]), and including longer follow-up (RR 0.79 [95% CI 0.66 to 0.94]), with no significant between-study heterogeneity. The relative risk reduction was largely similar in trials of patients with or without acute myocardial infarction (AMI), in trials continuing or discontinuing heparin after the procedure, and in trials using stents or another PCI as the intended primary procedure. Myocardial infarction and composite outcomes were significantly reduced (p < 0.001 for all) at 30 days and six months. Major bleeding was significantly increased only in trials where heparin infusion was continued after the procedure (RR 1.70 [95% CI 1.36 to 2.14]), although there was no excess bleeding when heparin was discontinued (RR 1.02 [95% CI 0.85 to 1.24]). CONCLUSIONS: In patients undergoing PCI, GP IIb/IIIa receptor antagonists confer a significant and sustained decrease (20% to 30%) in the risk of death.     

Abciximab in primary coronary angioplasty for acute myocardial infarction improves short- and medium-term outcomes

Objectives. The purpose of this study was to compare the outcome of primary percutaneous transluminal coronary angioplasty for acute myocardial infarction (MI) when performed with or without the platelet glycoprotein IIb/IIIa antibody, abciximab.

Background. Abciximab improves the outcome of angioplasty but the effect of abciximab in primary angioplasty has not been investigated.

Methods. Data were collected from a computerized database. Follow-up was by telephone or review of outpatient or hospital readmission records.

Results. A total of 182 consecutive patients were included; 103 received abciximab and 79 did not. The procedural success rate was 95% in the two groups. At 30-day follow-up, the composite event rate of unstable angina, reinfarction, target vessel revascularization and death from all causes was 13.5% in the group of patients who did not receive abciximab, 4% (p < 0.05) in the abciximab group and 2.4% (p < 0.05) in the subgroup of patients (n = 87) who completed the 12-h abciximab infusion. At the end of follow-up (mean 7 ± 4 months), the composite event rate was 32.4%, 17% (p < 0.05) and 13.1% (p < 0.01) in these three categories respectively. Abciximab bolus followed by a 12-h infusion was an independent predictor of event-free survival, in a Cox proportional hazards model (relative risk 0.49; 95% confidence interval 0.24 to 0.99; p < 0.05).

Conclusions. Abciximab given at the time of primary angioplasty may improve the short- and medium-term outcome of patients with acute MI, especially when a 12-h infusion is completed.     

Therapeutic heparin concentrations augment platelet reactivity: implications for the pharmacologic assessment of the glycoprotein IIb/IIIa antagonist abciximab

BACKGROUND: This study evaluated the effect of heparin on the platelet reactivity and the pharmacodynamic profile of abciximab. METHODS AND RESULTS: Ex vivo studies were performed on patients undergoing elective percutaneous coronary intervention (n = 26) who were at moderate to high risk of ischemic complications. Patients received a 12,000-U bolus of heparin followed by a 0.25-mg/kg bolus of abciximab. Before abciximab treatment, platelet aggregation responses to a variety of stimuli were assessed immediately before and 10 minutes after the heparin bolus. Heparin increased platelet aggregation to 2 and 5 micromol/L adenosine diphosphate (ADP) and 5 microg/mL collagen by 36%, 25%, and 46%, respectively (P < or =.001), but did not influence platelet reactivity to thrombin receptor-activating peptide or 20 micromol/L ADP and had no appreciable effect on platelet surface glycoprotein (GP) IIb/IIIa receptor numbers. To assess the impact of heparin on the pharmacodynamic profile of abciximab, GP IIb/IIIa receptor blockade and platelet aggregation inhibition estimates obtained after abciximab administration were calculated relative to the basal levels observed both before and after the heparin bolus. At 2 and 24 hours after the abciximab bolus, GP IIb/IIIa receptor blockade measurements normalized to either the preheparin or postheparin baseline determinations were equivalent. For all ADP concentrations tested, the 2-hour post-abciximab bolus platelet aggregation inhibition estimates based on the preheparin and postheparin baseline values were comparable. However, for 2 and 5 micromol/L ADP, the 24-hour post-abciximab platelet aggregation inhibition measurements based on preheparin baseline values were significantly lower than postheparin baseline determinations (both P < or =.003). In vitro studies revealed that therapeutic heparin doses induced a concentration-dependent reduction in the extent of platelet inhibition produced by amounts of abciximab that elicit partial inhibition of platelet aggregation. However, at abciximab concentrations that achieved platelet aggregation blockade of >80%, the levels of inhibition of platelet aggregation in the presence and absence of heparin were equivalent. CONCLUSIONS: The cumulative ex vivo and in vitro data indicate that for certain stimuli, heparin alters the platelet inhibitory profile of abciximab at concentrations of the agent that yield partial suppression of platelet function.     

Combining thrombolysis with the platelet glycoprotein IIb/IIIa inhibitor lamifiban: results of the Platelet Aggregation Receptor Antagonist Dose Investigation and Reperfusion Gain in Myocardial Infarction (PARADIGM) Trial

Objectives. The trial was designed to assess the safety, pharmacodynamics and effects on reperfusion of the platelet glycoprotein (GP) IIb/IIIa inhibitor lamifiban when given with thrombolysis to patients with ST segment elevation acute myocardial infarction.

Background. Studies of fibrinolytic agents in acute myocardial infarction have demonstrated a direct relationship between early complete reperfusion and survival. Blockade of the platelet GP IIb/IIIa receptor complex inhibits platelet aggregation and may speed reperfusion when given in conjunction with thrombolysis to patients with acute myocardial infarction.

Methods. Patients with ST segment elevation presenting within 12 h of symptom onset who were treated with either tissue-plasminogen activator or streptokinase were enrolled in this three-part Phase II dose exploration study. In Part A, all patients received the GP IIb/IIIa inhibitor lamifiban in an open-label, dose escalation scheme. Parts B and C were a randomized, double-blind comparison of a bolus plus 24-h infusion of lamifiban versus placebo with patients randomized in a 2:1 ratio. The goal was to identify a dose(s) of lamifiban that provided >85% adenosine diphosphate (ADP)-induced platelet aggregation inhibition. A composite of angiographic, continuous electrocardiographic and clinical markers of reperfusion was the primary efficacy end point, and bleeding was the primary safety end point.

Results. Platelet aggregation was inhibited by lamifiban in a dose-dependent manner with the highest doses exceeding 85% ADP-induced platelet aggregation inhibition. There was more bleeding associated with lamifiban (transfusions in 16.1% lamifiban-treated vs. 10.3% placebo-treated patients). Lamifiban induced more rapid reperfusion as measured by all continuous electrocardiographic (ECG) parameters.

Conclusions. Lamifiban given with thrombolytic therapy appears to be associated with more rapid and complete reperfusion than placebo. As expected in this small sample, there were no obvious clinical benefits to lamifiban over placebo. Reconciliation of ECG monitoring with clinical outcomes will require a larger, adequately powered clinical trial.     

Synthetic inhibitors of platelet glycoprotein IIb/IIIa in clinical development

Activation of the platelet glycoprotein (GP IIb/IIIa) receptor on the platelet surface is the final pathway of platelet aggregation, regardless of the initiating stimulus. Inhibitors of GP IIb/IIIa receptors include monoclonal antibodies (abciximab) against this receptor and peptidic and nonpeptidic synthetic specific receptor blockers. Abciximab exchanges between and binds to platelets for as long as 2 weeks, whereas synthetic GP IIb/IIIa inhibitors inhibit ex vivo platelet aggregation for only a few hours after the end of infusion, but some have the advantage of also being orally active. In the secondary prevention of atherothrombosis, large-scale trials were successfully conducted with aspirin, dipyridamole, ticlopidine, and clopidogrel. In the first large-scale trials with GP IIb/IIIa inhibitors, abciximab was investigated. In aggregate, synthetic GP IIb/IIIa inhibitors, combined with aspirin and heparin, were shown to reduce ischemic events in patients with high- and low-risk coronary intervention, stents, unstable angina, and non-Q-wave infarction. With short-term use of synthetic GP IIb/IIIa inhibitors, there is no suppression of clinical evident restenosis 6 months after the end of treatment. With the doses currently used, bleeding occurs more often with the synthetic GP IIb/IIIa inhibitors (used for 3 days) than with abciximab (used for 12 hours), but there are no direct comparisons between these drugs.