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Two trials of thrombolysis for acute myocardial infarction are contrasted and compared using a systematic approach developed for the interpretation of studies where equivalence is claimed. Reteplase has been compared with streptokinase in a true equivalence trial (International Joint Efficacy Comparison of Thrombolytics [INJECT] trial) and with tissue plasminogen activator in a failed superiority trial (Global Use of Strategies to Open Occluded Coronary Arteries [GUSTO] III). Important methodological distinctions and economic insights are highlighted. Using this approach one can conclude that the INJECT investigators have shown that reteplase is at least as effective as streptokinase and that the test for equivalence was satisfied. The point estimate of the treatment effect for the primary outcome event favours reteplase over streptokinase, and the confidence intervals essentially eliminate the possibility of streptokinase superiority. The GUSTO III primary outcome event, 30-day mortality, provides no convincing evidence that reteplase is equivalent to tissue plasminogen activator. Selective emphasis on one or two post hoc outcome event clusters, such as death and nonfatal stroke, or death and disabling stroke, provides some suggestive, but not conclusive, evidence for equivalence. Moreover, for some of the outcome events, and in particular the primary outcome event, the point estimate suggests that reteplase is, in fact, slightly less effective than tissue plasminogen activator.
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PMID:Evidence-based medicine and reteplase: inductive arguments over deductive reasoning. 1050 81

In acute myocardial infarction, early identification of patients at a high mortality risk is important for planning further therapeutic strategies. Previous studies have demonstrated that the extent of early resolution of ST-segment elevation may represent a simple, quick and noninvasive assessment to identify high risk groups of patients. In a subgroup of the COBALT Study population (Continuous Infusion vs Double Bolus Administration of Alteplase), ST-segment elevation was measured before and 90 to 120 minutes after treatment with alteplase. The subgroup of n = 1,760 patients was not different from the total COBALT population of n = 7169 patients regarding most clinical parameters except Killip Class before treatment. However, the overall 30-day mortality differed significantly between the main study and the substudy (7.76% vs 3.52%; p < 0.001). Three groups of ST-segment resolution were defined: 1. complete resolution (resolution > or = 70%; 762 patients), 2. partial resolution (< 70% and > 30%; 491 patients), 3. no resolution (< 30%; 507 patients). Mortality rate at 30 days for complete, partial and no resolution of ST-segment elevation was 1.31%, 4.28% and 6.11%, respectively (p < 0.001). While this significant correlation between the extent of ST-segment resolution and mortality could be observed for inferior acute myocardial infarction, it could not be found in patients with anterior acute myocardial infarction. This in part may be due to a selection bias that leads to an extremely divergent mortality rate of anterior acute myocardial infarction in the main study and the substudy (10.1% vs 3.94%; p < 0.0001). Despite this limitation, resolution of ST-segment elevation in acute myocardial infarction after thrombolytic therapy allows to identify patients at a high mortality risk and may help to select patients for early invasive procedures such as PTCA. Patients with complete ST-segment resolution showed a particularly low mortality rate, irrespective of the alteplase regimen used (front-loaded alteplase vs double bolus alteplase).
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PMID:Resolution of ST-segment elevation in acute myocardial infarction--early prognostic significance after thrombolytic therapy. Results from the COBALT trial. 1054 48

Several lines of research towards improvement of thrombolytic agents are being explored, including the construction of mutants of plasminogen activators, chimeric plasminogen activators, conjugates of plasminogen activators with monoclonal antibodies, and plasminogen activators from animal or bacterial origin. Some of these new thrombolytic agents have shown promise in animal models of venous or arterial thrombosis; only those which are being investigated in clinical studies are briefly discussed. Monteplase is a modified tissue type-plasminogen activator (t-PA) constructed by substituting only one amino acid in the epidermal growth factor domain (Cys84-->Ser) and expressed in baby Syrian hamster kidney cells. It has a prolonged half-life of more than 20 min, as compared to 4 min for native t-PA. TNK-t-PA differs from t-PA by 3 mutations. This mutant has increased thrombolytic potency, slower clearance and enhanced resistance to the inhibitor PAI-1. Reteplase is a non-glycosylated deletion mutant of wild-type human t-PA which contains only kringle 2 and the protease domain but lacks its kringle 1 and the finger and growth factor domains. The structural changes in reteplase translate into a decreased fibrin binding, a lower affinity to endothelial and liver cells resulting in an extended half-life. Lanoteplase is a deletion mutant of t-PA with a half-life that is circa 10 times greater than alteplase, making it suitable for single bolus injection. YM866 is another mutant of t-PA in which the aminoacids 92 to 173 of kringle 1 were deleted and arginine275 replaced by glutamic acid which confers a longer half-life to the mutant. Recombinant glycosylated prourokinase has a greater stability than recombinant unglycosylated pro-urokinase, is rapid acting and safe in the clinical doses used. Staphylokinase (SAK) is produced by Staphylococcus aureus. It induces efficient and rapid recanalization, also after bolus injection, but is immunogenic. There are only a few large scale clinical trials published directly comparing fibrin-selective thrombolytic drugs. In patients with acute myocardial infarction, reteplase, administered in bolus injections, is associated with a similar mortality and bleeding rate as front loaded t-PA. Bolus TNK-t-PA has a similar incidence of cerebral bleeding as front loaded t-PA and is associated with the same survival rate after acute myocardial infarction in a large mortality trial.
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PMID:Newer thrombolytic agents. 1057 30

Thrombolytic drugs, streptokinase and urokinase, were initially used in pulmonary embolism. More recently, new drugs like alteplase, reteplase, lanoteplase and saruplase have been a breakthrough in the treatment of acute myocardial infarction. Their efficacy has been demonstrated when treatment is initiated before the 6th hour of infarction onset. A 50% reduction of death rate is expected, if treatment starts within the 1st hour. Alteplase and reteplase are the most efficient thrombolytics despite a higher risk of cerebral bleeding. In pulmonary embolism with clinical signs of severity, thrombolysis is clearly indicated. In deep vein thrombosis of the lower limbs, therapeutic thrombolysis is still controversial. Some acute ischemic strokes (before the 3rd hour) could be treated with alteplase if there is no absolute or relative contraindication for thrombolysis. In prosthetic heart valve thrombosis, thrombolysis may be used if surgical treatment is contraindicated but the risk of bleeding and embolism should be taken into account.
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PMID:[Indications for thrombolytics]. 1058 97

Clinical trials in the 1990s of intravenous thrombolysis for ischaemic stroke have involved over 3000 patients. Alteplase given within 3 hours of onset significantly reduces the combined end-point of death and disability. Although alteplase appears safe when given up to 6 hours after onset, individual trials have failed to confirm efficacy beyond 3 hours. Meta-analysis indicates that intravenous alteplase given up to 6 hours after stroke onset significantly reduces death or dependence 3 months after stroke. Two trials of intra-arterial pro-urokinase confirm benefits of treatment up to 6 hours in highly selected patients with angiographically confirmed proximal middle cerebral occlusion. Streptokinase increased the risk of early death significantly in 3 trials, with no overall reduction in eventual death and disability. Patients over 80 years have been excluded from most trials of alteplase, and experience in this age group is minimal. Increased incidence and poorer functional outcome in the elderly mean that thrombolysis may have greater absolute benefit in this group than in the young, but there is also a higher prevalence of absolute or relative potential contraindications to treatment (ranging from increased use of anticoagulant drugs to higher prevalence of atrial fibrillation). Further trials are necessary to address age restrictions and other important issues in the use of alteplase. Thrombolysis is likely to remain feasible for a minority of stroke patients of all ages, and there is a need for other acute treatment options.
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PMID:Thrombolytic therapy for stroke: a review with particular reference to elderly patients. 1073 63

Alteplase is the most commonly administered thrombolytic agent in the United States. However, concurrent therapy with nitroglycerin reduces plasma alteplase concentrations and its clinical efficacy. We sought to determine if this interaction is concentration and pH dependent. Seventy plasma samples were prepared and divided into three groups: alteplase 500 IU/ml alone (group 1), alteplase 500 IU/ml plus nitroglycerin 5 ng/ml (group 2), and alteplase 500 IU/ml plus nitroglycerin 200 ng/ml (group 3). The samples were analyzed at time zero and 3 hours (incubated at 37 degrees C). Group 1 had significantly higher plasma alteplase concentrations than group 3 (p<0.001). When alteplase and nitroglycerin are combined, the degradation of alteplase in plasma is enhanced.
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PMID:Assessment of the drug interaction between alteplase and nitroglycerin: an in vitro study. 1077 66

Tenecteplase is a site-specific engineered tissue plasminogen activator (t-PA) variant that can be administered as a single intravenous bolus injection because of its slower plasma clearance. The objective of this study was to investigate the dose-ranging pharmacokinetics and pharmacodynamics of intravenous bolus tenecteplase compared with intravenous alteplase recombinant t-PA in patients with acute myocardial infarction. A total of 103 patients received intravenous bolus doses of 30, 40, or 50 mg tenecteplase, and 56 patients received 100 mg rt-PA as the accelerated 90-minute infusion regimen in this randomized, open-label study. Tenecteplase and r-tPA plasma concentrations were measured for 6 hours. Tenecteplase exhibited biphasic elimination from the plasma with a mean initial half-life of 22 minutes and a mean terminal half-life of 115 minutes. The mean plasma clearance was 105 mL/min and did not depend on tenecteplase dose over the dose range studied. In comparison, rt-PA has a fourfold faster plasma clearance. Pharmacokinetic-pharmacodynamic evaluation showed that a dose of approximately 0.5 mg/kg results in a plasma AUC value that provides a TIMI 3 flow at 90 minutes that is comparable to that reported with accelerated r-tPA. In conclusion, tenecteplase has a fourfold slower plasma clearance compared with rt-PA, allowing dosing as an i.v. bolus injection. Weight-adjusted dosing of tenecteplase may optimize the therapeutic regimen of tenecteplase.
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PMID:Pharmacokinetics and pharmacodynamics of tenecteplase: results from a phase II study in patients with acute myocardial infarction. 1080 4

This study was undertaken to compare the effects of reteplase and alteplase regimens on hemostasis and fibrinolysis in acute myocardial infarction (AMI). Thrombolytic treatment in patients with AMI is hampered by paradoxical procoagulant effects that favor early reocclusion. In vivo data comparing this effect and the fibrin specificity of double-bolus reteplase and front-loaded alteplase regimens are not available. In a prospective, randomized study, 50 patients with AMI were either treated with double bolus (10 + 10 U) reteplase or with front-loaded alteplase (up to 100 mg) within 6 hours of symptom onset. Thirty apparently healthy persons served as controls. Molecular markers of coagulation and fibrinolysis were serially examined for up to 5 days. Paradoxical thrombin activation at 3 hours after initiation of therapy was comparable between reteplase and alteplase. Reteplase (65 +/- 5 U/L) and alteplase (72 +/- 8 U/L) caused significantly elevated kallikrein activity at 3 hours after adminstration (p <0.01 vs controls 30 +/- 1 U/L). Fibrin specificity was less for reteplase (p <0.05) with a decrease in fibrinogen at 3 hours to 122 +/- 27 mg/dl versus 224 +/- 28 mg/dl for alteplase (p <0.01 and p <0.05 vs controls). D-Dimer levels at 3 hours were higher (p <0.05) after reteplase (5,459 +/- 611 ng/ml) versus alteplase (3,445 +/- 679 ng/ml) (both p <0.01 vs controls 243 +/- 17 ng/ml). Plasmin generation (plasmin-antiplasmin complexes) was significantly (p <0.01) increased at 3 hours with both regimens to 27,079 +/- 3,964 microg/L (reteplase) and 19,522 +/- 2,381 microg/L (alteplase). The data from 3 hours after start of thrombolytic therapy proved less marked fibrin specificity of the reteplase regimen (in vivo) compared with front-loaded alteplase. Both regimens have a moderate procoagulant effect without differences in activation of the kallikrein system.
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PMID:Fibrin specificity and procoagulant effect related to the kallikrein-contact phase system and to plasmin generation with double-bolus reteplase and front-loaded alteplase thrombolysis in acute myocardial infarction. 1092 30

We sought to determine the efficacy of the combination of argatroban, a direct thrombin inhibitor, and G4120, a platelet glycoprotein (GP) IIb/IIIa blocker, to enhance thrombolysis with alteplase. Platelet-rich thrombus in the rabbit arterial thrombosis model is relatively resistant to alteplase despite the addition of aspirin and heparin. The adjunctive use of either direct thrombin inhibitors or GP IIb/IIIa inhibitors in thrombolysis has been investigated with encouraging, but limited, success. The usefulness of combining both agents as adjunctive therapy to thrombolysis has not been fully explored. Following platelet-rich thrombus formation in the rabbit, argatroban (3 mg/kg), G4120 (0.5 mg/kg), G4120 plus heparin (200 U/kg), or G4120 plus argatroban were intravenously infused over 60 minutes. Alteplase was given as intravenous boluses (0.45 mg/kg) at 15-minute intervals up to 4 doses or until reperfusion. Blood flow and bleeding time were monitored for 2 hours. The combination of G4120 plus argatroban resulted in a persistent patency in 5 of 7 animals compared with 0 of 6 for argatroban alone (p=0.02), 1 of 6 for G4120 alone (p=0.08), and 2 of 6 for G4120 plus heparin (p=0.2). Although during the infusion the bleeding times were longer in the groups that received G4120 (26+/-7.7 minutes vs. 14+/-10 minutes, p<0.05), by the end of the experiment there were no statistically significant differences. Similarly, during the infusion the activated partial thromboplastin times (aPTT) was higher in groups that received heparin or argatroban (99+/-51 seconds vs. 32+/-7.6 seconds, p<0.001), but by the end of the experiment the aPTTs had returned to close to baseline in all groups except the G4120 plus heparin group. These results suggest that lysis of platelet-rich thrombus with alteplase requires the addition of both potent platelet and thrombin inhibitors. Specifically designed agents, G4120 and argatroban, are effective without additional increased risk for bleeding.
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PMID:Combination of a direct thrombin inhibitor and a platelet glycoprotein IIb/IIIa blocking peptide facilitates and maintains reperfusion of platelet-rich thrombus with alteplase. 1100 41

The optimal method of reperfusion for patients with ST-segment elevation acute myocardial infarction has been a point of controversy over the last two decades. Tenecteplase and reteplase are comparable to accelerated-dose alteplase but more convenient because they can be delivered as a bolus. Combination regimens represent a further advance in reperfusion therapy; planned and ongoing studies will evaluate the clinical efficacy and safety of combination therapy. Promising early results of primary coronary intervention with glycoprotein IIb/IIIa receptor inhibition have been reported, and this strategy may emerge as a mainstay of therapy at hospitals with on-site interventional facilities. A possible future approach that could be universally applied consists of combination therapy and adjunctive/rescue percutaneous intervention in selected patients.
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PMID:New Thrombolytic Agents: Does Direct Angioplasty Still Have a Role? 1109 74


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