Recombinant tissue plasminogen activator (rt-PA): is it the thrombolytic agent of choice for an evolving acute myocardial infarction?

Bafibrinase: A non-toxic, non-hemorrhagic, direct-acting fibrinolytic serine protease from Bacillus sp. strain AS-S20-I exhibits in vivo anticoagulant activity and thrombolytic potency

A non-toxic, direct-acting fibrinolytic serine protease (Bafibrinase) demonstrating thrombolytic and anticoagulant properties was purified from Bacillus sp. strain AS-S20-I. Bafibrinase was monomeric, with a molecular mass of 32.3 kDa. The peptide mass fingerprinting of Bafibrinase revealed only 8.3% sequence coverage, suggesting it was a novel fibrinolytic enzyme. However, two of the tryptic digested de novo peptide sequences of Bafibrinase demonstrated good similarity with endopeptidases possessing serine in their catalytic triad. Further, catalytic activity of Bafibrinase was inhibited by serine protease inhibitor reinforcing this is a subtilisin-like serine protease. The apparent K(m) and V(max) values of Bafibrinase towards fibrin were determined as 0.24 μM and 2.8 μmol/min, respectively. It showed a K(m) value of 0.139 mM towards a chromogenic substrate for plasmin (D-Val-Leu-Lys-p-Nitroanilide dihydrochloride) and optimum activity at physiological conditions (37 °C and pH 7.4). Based on the cleavage pattern of fibrin and fibrinogen, Bafibrinase may be classified as an α,β-fibrinogenase. Bafibrinase could not degrade collagen and was non-cytotoxic to HT29 cells or mammalian erythrocytes. Further, Bafibrinase at a dose of 2 mg/kg was devoid of toxicity as well as hemorrhagic activity on BALB/c mouse model, supporting its suitability for the development of a better and safer thrombolytic drug. Bafibrinase was also superior to human plasmin in degrading in vitro thrombus. The in vivo anticoagulant nature of Bafibrinase is being explored for the treatment and prevention of thrombosis and other cardiovascular diseases.

The fibrinolytic activity of a novel protease derived from a tempeh producing fungus, Fusarium sp. BLB

Tempeh is a traditional Indonesian soybean-fermented food produced by filamentous fungi, Rhizopus sp. and Fusarium sp. We isolated and sequenced the genomic gene and a cDNA clone encoding a novel protease (FP) from Fusarium sp. BLB. The genomic gene was 856 bp in length and contained two introns. An isolated cDNA clone encoded a protein of 250 amino acids. The predicted amino acid sequence of FP showed highest homology, of 76%, with that of trypsin from Fusarium oxysporum. The hydrolysis activity of FP toward synthetic peptide was higher than that of any other protease tested, including Nattokinases. Furthermore, the thrombolytic activity of FP was about 2.1-fold higher than that of Nattokinase when the concentration of plasminogen was 24 units/ml. These results suggest that FP is superior to Nattokinases in dissolving fibrin when absorbed into the blood.

Identification of a fibrinolytic enzyme by Bacillus vallismortis and its potential as a bacteriolytic enzyme against Streptococcus mutans

A potent fibrinolytic enzyme-producing bacterium was isolated from the traditional Korean condiment Chungkook-jang and identified as Bacillus vallismortis Ace02. The extracellular fibrinolytic enzyme was purified with a 18% recovery of activity from supernatant cultures using CM-Sepharose column chromatography and Sephacryl S-200 gel filtration. The specific activity of the purified enzyme was 757 kFU mg(-1). Its molecular mass was about 28 kDa and the initial amino acids of the N-terminal sequence were AQSVPYGVSQ. The full amino acid sequence of fibrinolytic enzyme Ace02 corresponded with bacteriolytic enzyme, L27, from Bacillus licheniformis, which has strong lytic activity against Streptococcus mutans, a major causative strain of dental caries. This suggests that the purified enzyme should be used for prevention of dental caries as well as being an effective thrombolytic agent.

Purification and characterization of fibrinolytic alkaline protease from Fusarium sp. BLB

Fusarium sp. BLB, which produces a strongly fibrinolytic enzyme, was isolated from plant leaf (Hibiscus). Fibrinolytic alkaline protease was purified from a culture filtrate of Fusarium sp. BLB by precipitation with (NH4)2(SO4) and column chromatography with CM-Toyopearl 650 M and Superdex 75. The purified enzyme was homogeneous on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The molecular weight was 27,000 by SDS-PAGE. Maximum activity of protease was observed at pH 9.5 and 50 degrees C. Purified protease was active between pH 2.5 and 11.5 and was found to be stable up to 50 degrees C. The enzyme derived from Fusarium sp. BLB is useful for thrombolytic therapy because this enzyme showed pH resistance. The activity was inhibited by diisopropylfluorophosphate and phenylmethylsulfonyl fluoride. The N-terminal amino acid sequence of the enzyme showed a similarity to those of proteases from Fusarium sp., Streptomyces griseus, Bos taurus bovine, Katsuwo pelamis digestive tract, and Lumbricus rubellus.

Fibrinolytic and antithrombotic protease from Spirodela polyrhiza

A fibrinolytic protease was purified from a Chinese herb (Spirodela polyrhiza). The protease has a molecular mass of 145 kDa and 70 kDa in gel filtration and SDS-polyacrlamide gel electrophoresis (PAGE), respectively, implying it is a dimer. Its optimum pH was 4.5-5.0. The enzyme was stable below 42 degrees C and after lyophilization. The enzyme activity was inhibited significantly by leupeptin and aprotinin. The protease hydrolyzed not only fibrin but also fibrinogen, cleaving Aalpha and Bbeta without affecting the gamma chain of fibrinogen. It preferentially cleaved the peptide bond of Arg or Lys of synthetic substrates (P1 position). The enzyme had an anticoagulating activity measured with activated partial thromboplastin time (APTT), thrombin time (TT), and prothrombin time (PT) tests. It delayed APTT, TT, and PT two times at the concentration of 36, 39, and 128 nM, respectively and this was drastically reduced after heat treatment.

Comparison of saruplase and alteplase in acute myocardial infarction. SESAM Study Group. The Study in Europe with Saruplase and Alteplase in Myocardial Infarction

Four hundred seventy-three patients with acute myocardial infarction (AMI) were treated with either saruplase (80 mg/hour, n = 236) or alteplase (100 mg every 3 hours, n = 237). Comedication included heparin and acetylsalicylic acid. Angiography was performed at 45 and 60 minutes after the start of thrombolytic therapy. When flow was insufficient, angiography was repeated at 90 minutes. Coronary angioplasty was then performed if Thrombolysis In Myocardial Infarction (TIMI) trial 0 to 1 flow was seen. Control angiography was at 24 to 40 hours. Baseline characteristics were similar. Angiography showed comparable and remarkably high early patency rates (TIMI 2 or 3 flow) in both treatment groups: at 45 minutes, 74.6% versus 68.9% (p = 0.22); and at 60 minutes 79.9% versus 75.3% (p = 0.26). Patency rates at 90 minutes before additional interventions were also comparable (79.9% and 81.4%). Angiographic reocclusion rates were not significantly different: 1.2% versus 2.4% (p = 0.68). After rescue angioplasty, angiographic reocclusion rates of 22.0% and 15.0% were observed. Safety data were similar for both groups. Thus, (1) early patency rates were high for saruplase and alteplase treatment, (2) reocclusion rates for both drugs were remarkably low, and (3) complication rates were similar. Thus, saruplase seems to be as safe and effective as alteplase.

Purification and characterization of a fibrinolytic enzyme produced from Bacillus sp. strain CK 11-4 screened from Chungkook-Jang

Bacillus sp. strain CK 11-4, which produces a strongly fibrinolytic enzyme, was screened from Chungkook-Jang, a traditional Korean fermented-soybean sauce. The fibrinolytic enzyme (CK) was purified from supernatant of Bacillus sp. strain CK 11-4 culture broth and showed thermophilic, hydrophilic, and strong fibrinolytic activity. The optimum temperature and pH were 70 degrees C and 10.5, respectively, and the molecular weight was 28,200 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The first 14 amino acids of the N-terminal sequence of CK are Ala-Gin-Thr-Val-Pro-Tyr-Gly-Ile-Pro-Leu-Ile-Lys-Ala-Asp. This sequence is identical to that of subtilisin Carlsberg and different from that of nattokinase, but CK showed a level of fibrinolytic activity that was about eight times higher than that of subtilisin Carlsberg. The amidolytic activity of CK increased about twofold at the initial state of the reaction when CK enzyme was added to a mixture of plasminogen and substrate (H-D-Val-Leu-Lys-pNA). A similar result was also obtained from fibrin plate analysis.

Pro-urokinase and prekallikrein are both associated with platelets. Implications for the intrinsic pathway of fibrinolysis and for therapeutic thrombolysis

The contact-dependent intrinsic pathway of fibrinolysis involving factor XII, prekallikrein (PK) and pro-urokinase (pro-UK) remains poorly understood. Casein autography of washed, intact platelets revealed both PK and pro-UK. Accordingly, platelets may mediate physiological thrombolysis by this pathway since factor XIIa activates PK and kallikrein activates pro-UK. Acid washing dissociated PK but not pro-UK from platelets. Exogenous pro-UK was specifically incorporated by platelets from the ambient fluid and similarly could not be dissociated from intact platelets. Therefore, platelets may also mediate an effect from therapeutically administered pro-UK by prolonging its half-life.

Comparison of results of intravenous infusion of anistreplase versus streptokinase in acute myocardial infarction

This randomized study compares the coronary perfusion rate in patients with acute myocardial infarction (AMI) treated with 2 different intravenous thrombolytic agents: streptokinase 1.5 million U given over 60 minutes and anisoylated human plasminogen streptokinase activator complex (anistreplase) administrated as a bolus of 30 U over 5 minutes. One hundred seventy-five patients (149 men and 26 women, mean age 54 years) have been included in this study. Eighty-nine patients were treated with anistreplase and 86 patients with streptokinase. AMI was inferior in 54 patients (61%) in the anistreplase group and in 54 patients (63%) in the streptokinase group. It was anterior in 35 (40%) and 32 (37%) patients, respectively. Coronary angiography and ventriculography were performed at a mean time (+/- SEM) of 207 +/- 11 minutes after the beginning of thrombolysis in 170 patients. A perfusion score grade of 2 or 3 according to the Thrombolysis in Myocardial Infarction trial was found in 63 patients (72%) in the anistreplase group and in 56 patients (68%) in the streptokinase group (p = NS). Severe bleeding occurred in 7 patients (8%) after anistreplase and in 6 patients (7%) after streptokinase. No cerebral hemorrhage occurred. Nine patients (5%) died during their hospital stay: 6 after anistreplase and 3 after streptokinase. It is concluded that intravenous administration of anistreplase or streptokinase is efficient and safe. Coronary patency 207 minutes after fibrinolysis, incidence of adverse events and mortality are similar in both groups.

Thrombolysis: the need for a critical review

The (Thrombolysis in Myocardial Infarction) TIMI-I trial led to the hypothesis that the greater reperfusion rate seen with recombinant tissue-type plasminogen activator (rt-PA) versus streptokinase would result in greater reductions in infarct size and mortality in patients with acute myocardial infarction. Despite extensive investigation, no trial comparing rt-PA with streptokinase (European Cooperative Study Group, Plasminogen Activator Italian Multicenter Study [PAIMS], Gruppo Italiano per lo Studio della Sopravvivenze nell'Infarto Miocardico [GISSI-2], International Study on Infarct Survival [ISIS-3], even TIMI-I itself) nor rt-PA and anisoylated plasminogen-streptokinase activator complex (APSAC or anistreplase) (Bassand, TEAM-3, ISIS-3), have confirmed this hypothesis. In a reversal of traditional scientific method, the studies, rather than the unconfirmed hypothesis, have been rejected. A lack of independent review of this subject may have contributed to this outcome. It is proposed that standards of review and editorial comment mandating true critical distance and independence be followed, permitting greater independence of scientific inquiry, review and debate.

Creation of the recombinant tissue plasminogen activator (rt-PA) image and its influence on practice habits

American physicians have commonly practiced thrombolytic therapy for acute myocardial infarction with the recombinant form of tissue plasminogen activator (rt-PA), although its cost is much higher than that of streptokinase. The greater popularity of rt-PA is based on the belief that it is a more effective and a safer drug for achieving myocardial salvage and mortality reduction. However, a series of studies testing this assumption have not substantiated its greater efficacy or safety with respect to not only streptokinase but also urokinase and anisoylated plasminogen-streptokinase activator complex (APSAC). This editorial reviews the sequence of events that led to the creation of the rt-PA image, the mistaken premises on which it was based and the questions that need to be addressed if we are to strengthen the scientific method for evaluating similar types of drugs and its influence on practice habits including the costs to the health system.

A randomized comparison of intravenous heparin with oral aspirin and dipyridamole 24 hours after recombinant tissue-type plasminogen activator for acute myocardial infarction. National Heart Foundation of Australia Coronary Thrombolysis Group

BACKGROUND

This study addressed the need for heparin administration to be continued for more than 24 hours after coronary thrombolysis with recombinant tissue-type plasminogen activator (rt-PA).

METHODS AND RESULTS

A total of 241 patients with acute myocardial infarction were treated with 100 mg rt-PA and a bolus of 5,000 units i.v. heparin followed by 1,000 units/hr i.v. heparin for 24 hours. At 24 hours, 202 patients were randomized to continue intravenous heparin therapy (n = 99) in full dosage or to discontinue heparin therapy and begin an oral antiplatelet regimen of aspirin (300 mg/day) and dipyridamole (300 mg/day) (n = 103). On prospective recording, there were no differences in the pattern of chest pain, reinfarction, or bleeding complications. Coronary angiography on cardiac catheterization at 7-10 days showed no differences in patency of the infarct-related artery. The proportion of patients with total occlusion (TIMI grade 0-1) of the infarct-related artery was 18.9% in the heparin group and 19.8% in the aspirin and dipyridamole group. In the patients with an incompletely occluded infarct-related artery, the lumen was reduced by 69 +/- 2% of normal in the heparin group and 67 +/- 2% in the aspirin and dipyridamole group. Left ventricular function assessed on cardiac catheterization and radionuclide study at day 2 and at 1 month showed no differences between the two groups. Left ventricular ejection fraction on radionuclide ventriculography at 1 month was 52.4 +/- 1.2% in the heparin group and 51.9 +/- 1.2% in the aspirin and dipyridamole group.

CONCLUSIONS

We conclude that heparin therapy can be discontinued 24 hours after rt-PA therapy and replaced with an oral antiplatelet regimen without any adverse effects on chest pain, reinfarction, coronary patency, or left ventricular function.

Detection, characterization and functional assessment of reperfused Q-wave acute myocardial infarction by cine magnetic resonance imaging

The capability of dynamic gradient-refocused magnetic resonance imaging (cine MRI) to detect, localize and functionally assess acute myocardial infarction (AMI) in 25 patients at a mean time interval of 7 days after AMI was evaluated. Fifteen asymptomatic volunteers were also examined to determine the specificity of the observations. Upon presentation, each patient received intravenous thrombolytic therapy, underwent immediate cardiac catheterization and had percutaneous transluminal coronary angioplasty performed when coronary reperfusion was absent. Twenty-four of the patients had documented coronary reperfusion at a mean interval of 259 +/- 129 minutes. Global ejection fraction and regional wall motion abnormalities were evaluated at 7 days by cine MRI, left ventriculography and radionuclide angiography. Twenty patients with both an absolute decrease in myocardial signal and a matched regional wall motion abnormality had AMI properly identified by cine MRI. In contrast, the finding of both decreased signal intensity and a matched regional wall motion abnormality was absent in the group of asymptomatic volunteers. The ejection fraction by cine MRI correlated better with the ejection fraction by left ventriculography (r = 0.94, standard error of the estimate = 3.6) than did the ejection fraction by radionuclide angiography (r = 0.82, standard error of the estimate = 5.8). The regional wall motion concordance rate in comparison to left ventriculography was similar for both cine MRI (69%) and radionuclide angiography (65%). These findings suggest that cine MRI may play an important role in the future detection and functional characterization of AMI.

Improved left ventricular function in myocardial infarction following intravenous thrombolytic therapy with acylated plasminogen activator

Forty-six patients with acute myocardial infarction (MI) were treated within three hours of the onset of chest pain with an intravenous bolus (IV) of 30 units of anisolated plasminogen activator streptokinase complex (APSAC). Reperfusion was detected in 31 patients (67%) by clinical, electrocardiographic, and enzymatic criteria. The mean time elapsed between the onset of the chest pain to thrombolytic therapy was 114 +/- 53 minutes. Left ventricular ejection fraction (LVEF) was significantly better in patients with anterior and inferior myocardial infarction who had successful reperfusion, as compared with those who did not (48.8 +/- 13.0 vs 35.3 +/- 10.9, p less than 0.05 and 59.7 +/- 12.6 vs 47.9 +/- 15.3, p less than 0.05, respectively). The rate of reocclusion within three weeks was 22%. The overall one-year mortality was 4%. There were no serious adverse reactions following the thrombolytic treatment. Thus bolus IV injection of 30 units of APSAC is both safe and effective in preserving left ventricular function when given early in the course of acute myocardial infarction.

Continuous rt-PA infusion as a salvage strategy to maintain patency of the infarct artery; safety of high cumulative dose and subsequent emergency coronary artery angioplasty and bypass surgery

Acute re-occlusion of an infarct artery reperfusion attained by thrombolytic therapy may be treated by emergency coronary angioplasty or bypass surgery. Repeated infusion of a thrombolytic agent is an additional treatment strategy. Three patients with reinfarctions that occurred very early after successful reperfusion were treated with continuous infusion of recombinant tissue-type plasminogen activator (rt-PA). These patients received a rt-PA dose of 300-360 mg while they awaited emergency mechanical revascularization procedures. Two patients had coronary angioplasty immediately after receiving repeated infusions of rt-PA and one underwent coronary bypass surgery while receiving a third rt-PA infusion. There were no bleeding complications in the 2 patients who underwent coronary angioplasty, and no excessive bleeding in the patient who received coronary bypass surgery. Thus, repeated continuous rt-PA infusions can be used to maintain the patency of recurrently occluding infarct arteries until definitive mechanical revascularization can be performed.

Acetylsalicylic acid 100 mg and 1000 mg daily in acute myocardial infarction suspects: a placebo-controlled trial

Of 1078 patients admitted to the coronary care unit with acute chest pain, 293 who had possible acute myocardial infarction and symptoms of median 4 h duration were randomized to treatment with acetylsalicylic acid (ASA) 100 mg daily, 1000 mg daily or placebo for 3 months. During hospitalization, the combined incidence of cardiac death and non-fatal myocardial infarction on-treatment (withdrawals not included) was significantly lower (P less than 0.02) in the 100 mg group (7.1%) than in both the 1000 mg group (20.8%) and the placebo group (19.7%). During later time periods of treatment and at all time periods analysed according to the intention-to-treat principle (withdrawals included), data suggested the same trend, but differences were not statistically significant. Collagen-induced platelet aggregation and serum thromboxane B2 were reduced to the same degree in the two ASA groups and were normal in the placebo group. The data suggest that low-dose ASA could be cheap and safe as first-aid therapy in myocardial infarction suspects.

[Antibody mediated thrombolysis. A new therapeutic principle]

Thrombosis of a coronary artery is the most common cause of myocardial infarction. Thrombolytic therapy, when instituted timely, has been shown capable of reducing morbidity and mortality. However, the use of presently available thrombolytic agents is associated with a bleeding tendency and efficacy is not optimal. This article reviews one of several lines of investigation that are presently being pursued in order to improve efficacy and specificity of thrombolytic therapy. The chemical conjugation of a fibrin specific monoclonal antibody and urokinase or tissue plasminogen activator results in markedly enhanced thrombolytic potency, both in vitro and in vivo. Specificity of the conjugates is greater than that of the parent plasminogen activators as reflected by conservation of fibrinogen, plasminogen and alpha-2 antiplasmin. A bispecific antibody, with specificity for both, fibrin and tissue plasminogen activator, has the potential of concentrating endogenous tissue plasminogen activator at the site of a thrombus. In the presence of the bispecific antibody, efficacy and specificity of tissue plasminogen activator are markedly enhanced in vitro and in vivo. The tools of molecular biology are presently being applied in order to translate these findings into better thrombolytic therapy.

Newer agents for coronary thrombolysis. Perspectives from clinical studies

Myocardial infarction (MI) is a major cause of morbidity and mortality in western countries and the formation of intracoronary thrombi is recognized as a critical determinant of this ischaemic event. Since streptokinase and urokinase cause in vitro lysis of clots, it was though that these drugs were also effective in vivo in dissolving coronary thrombi. Clinical studies supported this concept. However, the beneficial effects of these drugs were, to some extent, offset by their inherent adverse reactions. Therefore new thrombolytic agents were developed, and for three of them (APSAC, tPA and proUK) there are enough clinical studies to allow for a comparison with 'old' agents. The data show that none of the new agents is safer or better than old agents with respect to easy handling, incidence of reperfusion of occluded coronary arteries, frequency of reocclusions, thrombus specificity, and bleeding complications. Thus, several directions are currently pursued to develop newer thrombolytic drugs with risk/benefit ratios better than those of 'old' agents. In this respect, it has been shown recently that the combination of aspirin with streptokinase is significantly better than streptokinase alone as far as mortality and incidence of rethrombosis is concerned. These data suggest that thrombolytic approaches safer and better than those currently available are possible and indicate that some of such new strategies are already available to enter the 'thrombolytic era' of acute MI.

Plasminogen Activator Italian Multicenter Study (PAIMS): comparison of intravenous recombinant single-chain human tissue-type plasminogen activator (rt-PA) with intravenous streptokinase in acute myocardial infarction

A single chain preparation of recombinant tissue-type plasminogen activator (rt-PA) was compared with intravenous streptokinase to determine coronary thrombolytic efficacy in patients with acute myocardial infarction less than 3 h old. Eighty-six patients were randomly selected to receive the intravenous cumulative dose of 100 mg rt-PA and 85 patients to receive 1.5 million units streptokinase. At 240 min after initiation of the thrombolytic therapy noninvasive signs of sustained reperfusion occurred in 79% of patients in both groups (p = NS). Patency of the infarct-related vessel at follow-up angiography was observed in 81% of patients in the rt-PA group and 74% of patients in the streptokinase group (p = NS). At hospital discharge, compared with admission, echocardiographically determined left ventricular ejection fraction increased from 52 +/- 11% to 56 +/- 10% (p less than 0.01) in the rt-PA group; changes in the streptokinase group (50 +/- 9% to 51 +/- 11%) were not significant. A nadir value of less than 1 g/liter fibrinogen plasma level occurred in 6 patients (7%) receiving rt-PA versus 74 patients (87%) receiving streptokinase (p less than 0.0001). Plasma levels of fibrin(ogen) degradation products were more than doubled in the streptokinase group (p less than 0.01). One patient in the streptokinase group developed a fatal intracranial hemorrhage; five others showed a decline in hemoglobin greater than or equal to 5 g/dl. Other clinical events in the streptokinase-treated group included allergic reactions (four patients) and intrahospital reinfarction (two patients). None of these events occurred in the rt-PA group.(ABSTRACT TRUNCATED AT 250 WORDS)

Cost and efficacy of intravenous streptokinase plus PTCA for acute myocardial infarction when therapy is initiated in community hospitals

The costs and clinical results of a thrombolytic therapy protocol using intravenous (IV) streptokinase in small community hospitals prior to emergency transfer for cardiac catheterization for possible percutaneous transluminal coronary angioplasty (PTCA) were prospectively studied in 56 patients with an acute myocardial infarction [Tulsa Heart Center-Myocardial Infarction Study Team (THC-MIST) protocol]. Findings were compared to those for 53 similar patients receiving "conventional therapy" during the same study period. The reperfusion rate for IV streptokinase was 63%. Additional emergency PTCA yielded a total reperfusion rate of 95%. Despite emergency cardiac catheterization for all THC-MIST patients, average hospital charges were not significantly different between the two groups ($20,495 vs. $20,722; THC-MIST vs. conventional therapy, respectively). Total charges (hospital plus physician fees) were also not significantly different ($22,986 vs. $22,400; THC-MIST vs. conventional therapy, respectively). Intensive care unit (ICU) days and total hospital stays were significantly less for THC-MIST patients (3.1 vs. 5.8 ICU days, p less than 0.05 and 8.8 vs. 12.4 hospital days, p less than 0.05; THC-MIST vs. conventional therapy, respectively). Thus initiation of IV streptokinase in community hospitals for acute myocardial infarction with subsequent transfer for possible PTCA can yield high reperfusion rates without significantly increasing health care costs.

Trial of tissue plasminogen activator for mortality reduction in acute myocardial infarction. Anglo-Scandinavian Study of Early Thrombolysis (ASSET)

13,318 patients admitted to fifty-two coronary care units with suspected acute myocardial infarction were considered for inclusion in a double-blind study comparing recombinant tissue-type plasminogen activator (rt-PA) 100 mg plus heparin with placebo plus heparin. 8307 (62%) were excluded, mainly because their symptoms had begun more than 5 h previously, but all excluded patients were followed up at least until hospital discharge. 2516 patients were randomly allocated to rt-PA and 2495 to placebo. At one month the overall case fatality rates were 7.2% and 9.8%, respectively, a relative reduction of 26% (95% confidence interval 11-39%). 6.3% of patients given rt-PA had a bleeding complication (1.4% major) compared with 0.8% given placebo (0.4% major). However, the incidence of stroke was similar--1.1% in the rt-PA group and 1.0% in the placebo group. Subset analysis showed that patients who had a normal electrocardiogram (ECG) at the time of randomisation (17.5% of the whole trial population) had a low case fatality rate (1.6% in those given rt-PA compared with 3.0% in those given placebo). In those with an abnormal ECG at entry, rt-PA was associated with a 24.5% relative reduction in 1 month fatality (95% confidence interval 9-37%).

Unresolved clinical pharmacologic questions in thrombolytic therapy for acute myocardial infarction

Thrombolytic therapy has now become established as a useful therapeutic measure for the immediate treatment of an acute evolving transmural infarction. Nevertheless, several important and fundamental aspects of a pharmacologic nature remain to be resolved. Prominent among these is whether or not fibrin specificity of a thrombolytic agent provides important benefits, and whether heparin therapy as commonly employed to prevent rethrombosis has been effective. Review of the available data raises serious questions as to the validity of current views and the appropriateness of prevailing trends.

Efficacy of intravenous prourokinase and a combination of prourokinase and urokinase in acute myocardial infarction

Fifty-four patients with Q-wave acute myocardial infarction (AMI) were treated with heparin combined with intravenous single-chain urokinase-type plasminogen activator (prourokinase). To determine the optimal treatment regimen, prourokinase was applied in 3 different ways: group I received a bolus of 7.5 mg and a subsequent infusion of 40.5 mg over 60 minutes. Patency of the infarct artery was observed in 7 patients (50%) at the end of the infusion time. One hour after the end of the infusion the fibrinogen level had decreased to 87 +/- 12% of the preinfusion level; the plasminogen and alpha-2 antiplasmin levels to 61 +/- 13% and 59 +/- 34%, respectively. In group II prourokinase was administered as a 7.5 mg bolus followed by 66.5 mg over 60 minutes. Eleven patients (55%) had patent infarct-related coronary arteries and fibrinogen, plasminogen and alpha-2 antiplasmin levels had decreased to 58 +/- 29%, 38 +/- 18% and 21 +/- 14%, respectively. Group III was treated with a bolus of 3.7 mg prourokinase and 250,000 IU urokinase followed by 44.3 mg prourokinase, resulting in a patency rate of 65% (13 patients). Fibrinogen, plasminogen and alpha-2 antiplasmin levels decreased to 76 +/- 15%, 67 +/- 15% and 47 +/- 29%, respectively. Fibrin-specific thrombolysis can be achieved with glycosylated prourokinase. At higher dosages considerable systemic activation of the fibrinolytic system with little enhancement of the observed therapeutic effect occurred. The combination of prourokinase and urokinase yielded a higher patency rate than either dosage of prourokinase alone, although the difference was not statistically significant in this pilot trial.

Alteplase: a tissue plasminogen activator for acute myocardial infarction

Alteplase is a human tissue plasminogen activator (t-PA) produced by recombinant DNA technology. It is a relatively fibrin-specific thrombolytic agent, used primarily to lyse coronary artery clots. It has proven effective in the treatment of acute myocardial infarction (AMI). Despite continuous reevaluation of pharmacokinetic parameters for t-PA, limited distribution and clearance data mandate administration of t-PA as a continuous infusion. Tissue plasminogen activator is eliminated primarily by hepatic metabolism with an elimination half-life of five to ten minutes. Plasma levels show great interindividual variation but correlate with infusion rate and decrease in fibrinogen level. The current recommended dose is 100 mg administered as a 10-mg iv bolus followed by a continuous infusion over three hours. However, 40-150 mg has been used in clinical trials. The compound has undergone extensive testing, comparing it with placebo and streptokinase (SK), and combining it with angioplasty and coronary artery bypass surgery. Tissue plasminogen activator is effective at opening clotted coronary arteries in approximately 70 percent of AMI patients and has been shown to be approximately twice as effective as SK in one U.S. trial. Although there is considerable evidence of efficacy with t-PA, data evaluating the influence of t-PA on mortality are limited, but suggest a reduction to five percent. Currently, thrombolytic therapy is indicated for patients experiencing a transmural AMI with onset of symptoms within three to six hours before presenting to the emergency room. Active internal bleeding or conditions predisposing to serious hemorrhage are contraindications to thrombolytic therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Advances in thrombolytic therapy for acute myocardial infarction

There has been rapid proliferation of understanding and experience with thrombolytic therapy for acute myocardial infarction. Over the last few years, selective intracoronary infusion of lytic therapy has been replaced by intravenous administration because of the fundamental importance of time to reperfusion. Newer thrombolytic agents, such as tissue plasminogen activator (t-PA) and acylated streptokinase (APSAC), with properties distinct from streptokinase (SK) and urokinase, have been developed and have undergone extensive clinical trial evaluation. This review will focus primarily on the recent advances in thrombolytic therapy, with particular attention to efficacy, safety, and comparative aspects of the various agents currently or soon to be available.

The FDA Advisory Panel's decision on rt-PA

Considerable dissatisfaction has been expressed over the FDA's Cardio-renal Advisory Panel's recommendation on May 29, 1987 that approval of rt-PA as a thrombolytic agent for the treatment of acute myocardial infarction be delayed. Justification for the Advisory Panel's action appears to be based on a lack of adequate data supporting the clinical benefit and safety of a specific therapeutic regimen of rt-PA, i.e., its molecular form, dosage, and duration of therapy. Although not an issue in the Panel's decision, questions can be raised concerning claims that rt-PA, in comparison to streptokinase, is a safer agent as far as bleeding complications are concerned, and is twice as effective in dissolving coronary thrombi during a period of potential clinical benefit. Also to be considered is the association of its use with a higher incidence of rethrombosis and a much greater cost.