Benedikt Kohler

Flow Cytometric Monitoring of Glycoprotein IIb/IIIa Blockade and Platelet Function in Patients With Acute Myocardial Infarction Receiving Reteplase, Abciximab, and Ticlopidine Continuous Platelet Inhibition by the Combination of Abciximab and Ticlopidine

BackgroundImprovement of thrombolysis may be achieved by concomitant strong platelet inhibition. To monitor platelet function in patients with myocardial infarction (n=46) who were treated with the fibrinolytic agent reteplase, the glycoprotein (GP) IIb/IIIa blocker abciximab, and the ADP receptor antagonist ticlopidine, we developed a flow cytometric assay. Methods and ResultsBinding of abciximab to platelets was directly monitored as the percentage of platelets stained by a goat anti-mouse antibody. Blood drawn 10 minutes and 2 hours after the start of therapy with reteplase and abciximab and during the 12-hour infusion of abciximab demonstrated a maximal blockade of GP IIb/IIIa (10 minutes, 86.2±10.3%; 12 hours, 85.8±7.1%). Starting at 24 hours, abciximab binding gradually decreased (24 hours, 74.6±16.2%; 48 hours, 66.8±14.9%; 72 hours, 60.5±16.7%; 96 hours, 49.4±17.8%; 120 hours, 35.8±16.4%; and 144 hours, 29.9±15.3%). Binding of a chicken anti-fibrinogen antibody to platelets, indicating the level of functional blockade of GP IIb/IIIa, was inversely correlated with the binding of abciximab (r =−0.72, P <0.0001). In blood drawn at 10 minutes, platelet aggregation was maximally inhibited but recovered within 48 hours even if the majority of GP IIb/IIIa receptors were still blocked by abciximab. Reteplase did not influence abciximab binding and did not activate platelets, as measured by P-selectin expression, fibrinogen binding, and platelet aggregation. Platelet inhibition that was achieved during the first 24 hours by abciximab was directly maintained by additional treatment with ticlopidine. ConclusionsFlow cytometric monitoring of platelet function allows differentiation of the effects of reteplase, abciximab, and ticlopidine. The combination of abciximab and ticlopidine is an attractive therapeutic strategy that provides a fast and continuous platelet inhibition.

Platelet Function During and After Thrombolytic Therapy for Acute Myocardial Infarction With Reteplase, Alteplase, or Streptokinase

BACKGROUND Changes in platelet aggregation (PA) and platelet surface receptor expression induced by thrombolytic therapy for acute myocardial infarction may influence the rate of initial reperfusion and early reocclusion. METHODS AND RESULTS In the RAPID-1 (Reteplase Angiographic Phase II International Dose-finding study), RAPID-2 (Reteplase vs Alteplase Patency Investigation During myocardial infarction), INJECT (INternational Joint Efficacy Comparison of Thrombolytics), and GUSTO-3 (Global Use of Strategies To Open occluded coronary arteries) trials, 126 patients were enrolled in a single center. Patients were treated with either conventional alteplase (100 mg/180 min; n=15), accelerated alteplase (100 mg/90 min; n=21), reteplase 10+10-U double bolus (n=50), reteplase 10+5-U double bolus (n=15), reteplase 15-U single bolus (n=15), or streptokinase (1.5 MU/60 min; n=10). PA (after stimulation with ADP), P-selectin expression and fibrinogen binding to glycoprotein (GP) IIb/IIIa (determined by flow cytometry with and without stimulation with ADP), and levels of soluble P-selectin, prothrombin fragments F1 and F2, thrombin-antithrombin complexes (TAT), and antithrombin III (ATIII) were determined. PA decreased significantly at 1 and 2 hours in patients treated by 10+10-U reteplase or by streptokinase. Fibrinogen binding to platelet GP IIb/IIIa followed a similar pattern. Significant thrombin generation and significantly elevated thrombin levels during thrombolysis were reflected by increased F1 and F2 fragments and TAT levels in all treatment groups. ATIII levels decreased significantly during thrombolytic therapy. CONCLUSIONS A decrease in PA in patients treated by reteplase or streptokinase compared with alteplase could be observed in the early phase. Double bolus (10+10 U) reteplase and streptokinase resulted in lower PA at 1 and 2 hours than therapy with accelerated alteplase. Total fibrinogen and fibrinogen binding to GP IIb/IIIa tended to be lower during the first 2 hours after reteplase than after accelerated alteplase.

Ecarin Clotting Time but not aPTT Correlates with PEG-Hirudin Plasma Activity

AbstractBackground: Novel antithrombotic agents such as hirudin have shown promise in the therapy of acute coronary syndromes. PEG-hirudin (polyethyleneglycol conjugated hirudin) has been developed to provide a longer plasma half-life and more stable antithrombotic plasma levels. Privious trials indicated a narrow therapeutic window for hirudin and a number of aPTT (activated partial thromboplastin time)-monitored trials investigating hirudin in acute coronary syndromes had to be stopped because of intracranial bleeding complications. Objectives: The present study evaluates the ecarin clotting time (ECT), a parameter based on the conversion of prothrombin by the snake venom enzyme ecarin, for the monitoring of PEG-hirudin therapy. Methods: Plasma from either healthy volunteers (n=20) or from patients (n=10) suffering from unstable angina pectoris (UAP) was spiked with increasing PEG-hirudin concentrations. In a prospective randomized clinical trial patients with UAP were treated with intravenous PEG-hirudin or heparin over 72 hours. Patients were randomized to the following treatment groups: (1) heparin control group, n=15; (2) PEG-hirudin low dose (0.1[emsp4 ]mg/kg bolus, 0.01[emsp4 ]mg/kg/h infusion), n=19; (3) intermediate dose (0.15[emsp4 ]mg/kg and 0.015[emsp4 ]mg/kg/h), n=17; 4) high-dose (0.2[emsp4 ]mg/kg and 0.02[emsp4 ]mg/kg/h), n=16. Spiked plasma samples and plasma from UAP patients treated with i.v. PEG-hirudin were analyzed for aPTT, ECT, and PEG-hirudin levels. Results: A linear correlation up to the highest therapeutic concentrations could be observed between PEG-hirudin plasma concentrations and the ECT. This was true for both plasma samples spiked with PEG-hirudin in vitro as well as for samples taken from patients treated with i.v. PEG-hirudin (correlation coefficient 0.9, respect.) In contrast the aPTT did not show a reliable linear correlation to PEG-hirudin concentrations. Conclusion: Monitoring of PEG-hirudin therapy by ECT may help to avoid inadequate anticoagulation or overdosing. Thus, the safety and efficacy profile of PEG-hirudin therapy is likely to be enhanced by ECT monitoring.Background: Novel antithrombotic agents such as hirudin have shown promise in the therapy of acute coronary syndromes. PEG-hirudin (polyethyleneglycol conjugated hirudin) has been developed to provide a longer plasma half-life and more stable antithrombotic plasma levels. Privious trials indicated a narrow therapeutic window for hirudin and a number of aPTT (activated partial thromboplastin time)-monitored trials investigating hirudin in acute coronary syndromes had to be stopped because of intracranial bleeding complications. Objectives: The present study evaluates the ecarin clotting time (ECT), a parameter based on the conversion of prothrombin by the snake venom enzyme ecarin, for the monitoring of PEG-hirudin therapy. Methods: Plasma from either healthy volunteers (n=20) or from patients (n=10) suffering from unstable angina pectoris (UAP) was spiked with increasing PEG-hirudin concentrations. In a prospective randomized clinical trial patients with UAP were treated with intravenous PEG-hirudin or heparin over 72 hours. Patients were randomized to the following treatment groups: (1) heparin control group, n=15; (2) PEG-hirudin low dose (0.1[emsp4 ]mg/kg bolus, 0.01[emsp4 ]mg/kg/h infusion), n=19; (3) intermediate dose (0.15[emsp4 ]mg/kg and 0.015[emsp4 ]mg/kg/h), n=17; 4) high-dose (0.2[emsp4 ]mg/kg and 0.02[emsp4 ]mg/kg/h), n=16. Spiked plasma samples and plasma from UAP patients treated with i.v. PEG-hirudin were analyzed for aPTT, ECT, and PEG-hirudin levels. Results: A linear correlation up to the highest therapeutic concentrations could be observed between PEG-hirudin plasma concentrations and the ECT. This was true for both plasma samples spiked with PEG-hirudin in vitro as well as for samples taken from patients treated with i.v. PEG-hirudin (correlation coefficient 0.9, respect.) In contrast the aPTT did not show a reliable linear correlation to PEG-hirudin concentrations. Conclusion: Monitoring of PEG-hirudin therapy by ECT may help to avoid inadequate anticoagulation or overdosing. Thus, the safety and efficacy profile of PEG-hirudin therapy is likely to be enhanced by ECT monitoring.

New developments in thrombolytic therapy

Summary Large efforts have been undertaken to develop more effective and safer thrombolytic agents than those currently used in clinical practice. In addition, the value of adjunctive agents influencing thrombotic and thrombolytic processes could be shown and newer agents are under active investigation. This review focuses on theoretical and practical aspects of optimizing thrombolytic therapy and mainly on genetically engineered, third generation plasminogen activators. Optimized thrombolytic therapy may make this form of therapy available to patients that are currently considered ineligible and it will lead to earlier, more complete reperfusion of infarct-related coronary arteries. The benefits and risks of optimized thrombolytic regimens relative to mechanical reperfusion strategies will have to be constantly reassessed as both forms of treatment develop.

Reteplase (r-PA): a new plasminogen activator

Reteplase (r-PA) is a genetically engineered deletion mutant of wild-type tissue-type plasminogen activator. The structural differences lead to different functional properties, such as a prolonged half-life. The compound demonstrated good thrombolytic efficacy in in vitro as well as in animal studies. In angiographically controlled patency studies (GRECO, GRECO-2 RAPID-1, RAPID-2), the double-bolus application scheme was established, and a superior patency profile for reteplase in comparison to alteplase was demonstrated. Mortality studies established reteplase as a safe drug with a 30-day mortality at least equivalent to streptokinase (INJECT) and very similar to alteplase (GUSTO-3). A possible advantage may be the double-bolus application without a need for weight adjustment, especially in a prehospital setting. Thus, reteplase can be regarded as an excellent alternative to streptokinase or alteplase for thrombolytic therapy in acute myocardial infarction.

Recombinant Plasminogen Activators

SummaryThrombolytic therapy has been shown to reduce mortality after acute myocardial infarction. Great efforts have been undertaken in the past decade to develop more efficient thrombolytic regimens. Novel recombinant thrombolytic substances have been engineered. Reteplase, a deletion mutant of wild-type tissue plasminogen activator with a longer half-life, has been evaluated in clinical trials and is now available for clinical use.In the randomised Reteplase Angiographic Phase II International Dose-Finding (RAPID-1) trial, involving 606 patients with acute myocardial infarction, a double-bolus regimen of reteplase (10 + 10U given 30 minutes apart) achieved significantly higher patency rates at 90 minutes after initiation of thrombolytic therapy than a 10 + 5U double-bolus reteplase regimen, a 15U single bolus reteplase regimen, or a conventional alteplase regimen (100mg in 180 minutes). In the Reteplase versus Alteplase Patency Investigation During Acute Myocardial Infarction (RAPID-2) trial, the reteplase 10 + 10U double-bolus regimen was more effective with regard to patency at 60 and 90 minutes than accelerated alteplase (100mg in 90 minutes). The International Joint Efficacy Comparison of Thrombolytics (INJECT) trial showed that a double-bolus regimen of reteplase 10 + 10U was at least equivalent to streptokinase in terms of 35-day mortality rate. The third Global Utilization of Strategies to Open Occluded Coronary Arteries (GUSTO-III) trial resulted in similar 30-day mortality after therapy with double-bolus reteplase 10 + 10U (7.47%) or accelerated alteplase (7.24%).Hence, the higher early patency rates achieved with reteplase treatment did not translate into improved survival. Consequently, there is still some uncertainty as to whether or not these drugs are equivalent.

Antithrombotische Prävention und Therapie bei koronarer Herzerkrankung

Zum ThemaIn der medikamentösen antithrombotischen Prävention der koronaren Herzkrankheit und ihrer Komplikationen nimmt die plättchenaggregierende Substanz Azetylsalizylsäure (ASS) eine einsame Spitzenpositione in. ASS wurde als Schmerzmittel 1897 durch F. Hoffmann erstmals synthetisiert und 1899 unter dem Namen Aspirin patentiert. Seit dieser Zeit ist es die weltweite Nummer Eins in jeder Hausapotheke und so bekannt, daß sogar sein erster Warenzeichenname Aspirin im wissenschaftlichen angloamerikanischen Schrifttum der generischen Bezeichnung vorgezogen wird.Seit Ende der 60er Jahre ist die plättchenaggregationshemmende Wirkung von ASS bekannt, seit 1971 auch der Wirkungsmechanismus. ASS ist vielen Multicenterstudien und mit bis dahin unbekannten riesigen Fallzahlen sowohl für die Primärprophylaxe (in der größten Studie ca. 22000 Personen) als auch für die Sekundärprophylaxe (in der größten Studie ca. 18000 Patienten) getestet worden.Gesicherte Indikationen für ASS bestehen primärprophylaktisch bei stabiler und instabiler Angina pectoris. Für eine generelle Empfehlung einer Anwendung bei symptomlosen Personen kann man sich wegen möglicher Nebenwirkungen nicht entschließen, wenngleich bei älteren Personen mit möglichen kardio- und zerebralvaskulären eine ASS-Prophylaxe wünschenswert erscheint.In der Sekundärprophylaxe besteht für ASS die Indikation zur Reinfarktprophylaxe, bei linksventrikulären Thromben und Thrombembolien, bei Koronarinterventionen und nach Bypassoperation. Andere Medikamente, über deren Wirkung auch in der ausführlichen Übersicht berichtet wird, spielen gegenüber ASS eine sehr viel geringere Rolle, nicht zuletzt auch aus Kostengründen.

Novel Tissue Plasminogen Activators: Reteplase (R-PA)

Thrombolytic therapy has become an accepted form of treatment for acute myocardial infarction. The GUSTO I trial showed that mortality reduction correlates with early, complete, and sustained patency of the infarct-related coronary artery [1],[2]. Current thrombolytic regimens achieve patency 90 minutes after initiation of treatment in only about 81% of cases, and only about 54% experience complete (TIMI grade 3) reperfusion. These results are obtained 90 minutes after initiation of therapy, and earlier patency rates are even more disappointing. Early reocclusion further limits the preservation of left ventricular function. In addition, even though patients are carefully selected, bleeding, especially intracranial bleeding, is a feared side effect, limiting the applicability of this form of treatment. In order to improve the risk/benefit ratio of thrombolytic therapy for patients, a number of new thrombolytic agents are being developed, primarily with the aim of reducing mortality by establishing more rapid, more complete, and more stable coronary patency.