Platelet function normalization after a prasugrel loading-dose: time-dependent effect of platelet supplementation.

BACKGROUND: Hemostatic benefits of platelet transfusions in thienopyridine-treated acute coronary syndrome (ACS) patients may be compromised by residual metabolite in circulation. OBJECTIVES: To estimate the earliest time after a prasugrel loading-dose when added platelets are no longer inhibited by prasugrel's active metabolite. METHODS: Baseline platelet reactivity of healthy subjects (n=25, 30 ± 5 years, 68% male) on ASA 325 mg was tested using maximum platelet aggregation (MPA, ADP 20 µm) and VerifyNow(®) P2Y12 and was followed by a 60 mg prasugrel loading-dose. At 2, 6, 12 and 24 h post-dose, fresh concentrated platelets from untreated donors were added ex-vivo to subjects' blood, raising platelet counts by 0% (control), 40%, 60% and 80%. To estimate the earliest time when prasugrel's active metabolite's inhibitory effect on the added platelets ceases, platelet function in supplemented samples was compared across time-points to identify the time when effect of supplementation on platelet function stabilized (i.e. the increase in platelet reactivity was statistically similar to that at the next time-point). RESULTS: Supplemented samples showed concentration-dependent increases in platelet reactivity vs. respective controls by both MPA and VerifyNow(®) at all assessment time-points. For each supplementation level, platelet reactivity showed a sharp increase from 2 to 6 h but was stable (P=NS) between 6 and 12 h. CONCLUSIONS: The earliest measured time when supplemented platelets were not inhibited by circulating active metabolite of prasugrel was 6 h after a prasugrel loading-dose. These findings may have important implications for prasugrel-treated ACS patients requiring platelet transfusions during surgery.

Normalization of platelet reactivity in clopidogrel-treated subjects.

BACKGROUND: Aspirin (ASA) + clopidogrel are commonly used in acute coronary syndrome (ACS), but persistent antiplatelet effects may complicate surgery. METHODS AND RESULTS: To study the possibility of normalizing platelet reactivity after ASA + clopidogrel treatment, 11 healthy subjects received a 325-mg ASA + clopidogrel loading dose (300 or 600 mg dependent on study arm), followed by 81 mg of ASA + 75 mg of clopidogrel daily for 2 days. Platelet reactivity was assessed by light transmittance aggregometry (LTA) [challenged by adenosine diphosphate (ADP), arachidonic acid (AA), collagen, and thrombin receptor activating peptide (TRAP)] and flow cytometry for platelet activation by GPIIb/IIIa receptor exposure pretreatment, 4 and 72 h postload. To normalize platelet reactivity, increasing amounts of pooled platelets from five untreated volunteers [volunteers (V)-platelet-rich plasma (PRP)] were added ex vivo to the subject's PRP (S-PRP). At both 4 and 72 h, 40% and 50% V-PRP were needed to overcome platelet disaggregation in the 300 or 600 mg arms, respectively, after ADP challenge; an additional 10% V-PRP fully normalized aggregation. Recovery of function was linear with each incremental increase of V-PRP. ADP-induced GPIIb/IIIa activation showed the same pattern as LTA (r = 0.74). Forty percent V-PRP was required to normalize platelet function to AA, collagen, and TRAP. CONCLUSION: Our results suggest that the pre-operative transfusion of 10 platelet concentrate units (the equivalent of 40% V-PRP) after a 300-mg clopidogrel loading or 12.5 units (50% V-PRP) after a 600 mg loading may adequately reverse clopidogrel-induced platelet disaggregation to facilitate postoperative hemostasis. An additional 2.5 units fully normalized platelet function. The potential clinical implications of our observations could include shorter hospitalizations and reduced bleeding complications. But these observations should be fully explored in an in vivo clinical setting with clopidogrel-treated patients before and after surgery.

Platelet glycoprotein IIb/IIIa inhibitors for acute coronary syndromes: initiate treatment early or wait for the catheterization laboratory?

Treatment of patients with acute coronary syndromes (ACS) incorporates several approaches to reverse or mitigate the thrombus, which invariably is at the center of the pathophysiologic process of ACS. Pharmacologic and mechanical strategies are designed to prevent death, reduce myocardial necrosis, and stabilize the plaque to prevent later sequelae. Conventional antithrombotic therapy includes antiplatelet and anticoagulant drugs. Medications that inhibit the platelet glycoprotein IIb/IIIa receptor have been shown to be especially efficacious in the treatment of ACS. Recent clinical trials have validated a strategy of aggressive revascularization, particularly catheter-based percutaneous procedures. This review summarizes new trial results and provides a working algorithm for care of the patient with ACS.

Pharmacodynamics and pharmacokinetics of eptifibatide in patients with acute coronary syndromes: prospective analysis from PURSUIT.

BACKGROUND: Platelet deposition and aggregation are central to the pathogenesis of ischemic complications of acute coronary syndromes (ACS). Pharmacodynamic effects of the platelet glycoprotein IIb/IIIa antagonist eptifibatide have been delineated in healthy subjects but not in patients with ACS. We assessed effects of eptifibatide on ex vivo platelet aggregation in patients enrolled in the Platelet glycoprotein IIb/IIIa in Unstable angina: Receptor Suppression Using Integrilin (eptifibatide) Therapy (PURSUIT) trial of ACS. METHODS AND RESULTS: Patients were randomly assigned to an intravenous bolus (180 microgram/kg) and 72-hour infusion of eptifibatide (2.0 microgram/kg per minute, n=48) or placebo (n=50). We assessed correlations of plasma eptifibatide levels with receptor occupancy and inhibition of ex vivo platelet aggregation at 5 minutes and 1, 4, 24, 48, and 72 hours during treatment and 4 and 8 hours after termination of infusion. Blood was collected in buffered citrate and D-phenylalanyl-L-prolyl-L-arginine chloromethylketone anticoagulants. Although eptifibatide produced profound, prolonged inhibition of platelet aggregation during therapy, aggregation appeared to recover partially by 4 hours after the bolus. The aggregation response was greater with thrombin receptor agonist peptide versus ADP stimulation; inhibition of platelet aggregation was greater in blood samples anticoagulated with citrate versus D-phenylalanyl-L-prolyl-L-arginine chloromethylketone (PPACK). Plasma eptifibatide levels correlated significantly with receptor occupancy but not with inhibition of platelet aggregation. CONCLUSIONS: A bolus and infusion of eptifibatide inhibits platelet aggregation profoundly in patients with ACS and is followed by brief, partial recovery. These results enhance our understanding of the relation between pharmacodynamic and clinical effects of eptifibatide in such patients and may have important implications for its use in percutaneous interventions.

Statins and cardiovascular diseases: the multiple effects of lipid-lowering therapy by statins.

Cholesterol lowering involving different therapies improves the clinical outcome of patients. To define the underlying pathomechanism, we studied whether treatment with statins was associated with changes in blood thrombogenicity, endothelial dysfunction and soluble adhesion molecule levels. Fifty hypercholesterolemic patients were treated with pravastatin (40 mg/day, n=24) or simvastatin (20 mg/day, n=26). Lipid profile and blood thrombogenicity were assessed in all patients before and after 3 months of cholesterol reducing therapy. Blood thrombogenicity was assessed as thrombus formation, perfusing non-anticoagulated blood directly from the patients' vein through the Badimon perfusion chamber (shear rate 1690/s). Endothelial-dependent vasomotor response was tested by laser-Doppler flowmeter. Soluble adhesion molecule level were measured by ELISA. Total and LDL cholesterol were reduced in the two treatment groups by statin therapy. Statin therapy was associated with a significant reduction in blood thrombogenicity and endothelium-dependent vasoresponse. No differences were observed between simvastatin or pravastatin treatment. Lipid lowering by statins had no effect on plasma levels of fibrinogen, sL-selectin, sP-selectin and sICAM-1 antigen. Cholesterol lowering by both statins reduced the increased blood reactivity and endothelial dysfunction present under hypercholesterolemia. The multiple effects of lipid lowering therapy by statins may explain the benefits observed in recent epidemiological trials.

Platelet glycoprotein IIb/IIIa receptor antagonists in cardiovascular disease.

CONTEXT: Thrombus formation on disrupted atherosclerotic plaque is the major cause of acute coronary events. Platelet inhibitors are the mainstay of drug therapy to reduce cardiac events in patients with acute coronary syndromes. The platelet glycoprotein (GP) IIb/IIIa receptor is the final common pathway of platelet aggregation. OBJECTIVES: To review mechanisms of platelet activation and aggregation and the role of the GP IIb/IIIa receptor in the acute coronary syndromes and to summarize completed clinical trials of GP IIb/IIIa receptor antagonists. DATA SOURCES: English-language journal articles, reviews from a MEDLINE search from 1993 through 1998, as well as abstracts and presentations from major national or international cardiology meetings through November 1998. STUDY SELECTION/DATA EXTRACTION: Randomized, placebo-controlled clinical trials testing intravenous GP IIb/IIIa receptor antagonists and having more than 500 subjects were included. Data quality and validity included publication or presentation venue. DATA SYNTHESIS/CONCLUSIONS: The GP IIb/IIIa receptor is the final common pathway of platelet aggregation. Intravenous monoclonal antibody and peptide and nonpeptide antagonists of the GP IIb/IIIa receptor have been tested in randomized, placebo-controlled trials of the acute coronary syndromes and percutaneous coronary interventions. For patients undergoing percutaneous revascularization, these agents have demonstrated efficacy in reducing death, myocardial infarction, or urgent reintervention. Odds ratios of death or myocardial infarction at 30 days range from 0.42 to 0.84 for the drugs in these studies. More modest benefits have been seen in trials of IIb/IIIa receptor antagonists for patients with the acute coronary syndromes, with odds ratios for death or myocardial infarction at 30 days ranging from 0.70 to 0.89. The efficacy of oral agents for chronic GP IIb/IIIa receptor antagonism has not been sufficiently studied.

Current state of thrombolytic therapy.

More than 200,000 people have been enrolled into clinical trials examining different reperfusion strategies for patients with acute myocardial infarction. Each year approximately 1 million people in the United States experience acute myocardial infarction. Thrombolytic agents, including streptokinase and tissue-type plasminogen activator, activate plasminogen. These agents are often divided into "fibrin-specific" and "non-fibrin-specific" drugs. New thrombolytic agents designed to address several of the shortcomings of existing thrombolytics are in various stages of clinical development.