Coronary thrombolysis with recombinant tissue-type plasminogen activator. A hematologic and pharmacologic study

Pharmacokinetics and pharmacodynamics of low doses of recombinant tissue plasminogen activator to establish a model for biosimilarity comparisons

Background

Recombinant tissue plasminogen activator (rt-PA) is a thrombolytic agent and essential in emergency medical care. Given recent supply shortages, the availability of biosimilar products is an urgent medical need. However, biosimilarity trials are difficult to perform in critically ill patients.

Objectives

The aim of this pilot study was to investigate the pharmacokinetics and pharmacodynamics of low rt-PA doses to establish a model for testing proposed biosimilars in healthy volunteers.

Methods

Eight healthy volunteers received 0.02 to 0.05 mg/kg rt-PA on 3 study days; blood samples were obtained every 4 minutes after the end of the bolus infusion to measure rt-PA antigen levels by enzyme immunoassay, and the pharmacodynamics were assessed with rotational thromboelastometry.

Results

Bolus infusion of low rt-PA doses was safe and well tolerated. Maximal plasma concentrations and the area under the curve increased dose-dependently. Time-concentration curves were clearly separated between the lower and the higher doses. As expected, the half-live of rt-PA was short (4.5-5 min), and representative for therapeutic doses. The intrasubject coefficient variations were moderate (<25%). Bolus infusion of rt-PA dose-dependently shortened lysis time and lysis onset time in both dose groups and caused maximum clot lysis of 100% in all participants.

Conclusion

In conclusion, the pharmacokinetics of rt-PA was dose linear and displayed limited intrasubject variability even at subtherapeutic doses. The half-life and thus clearance of rt-PA was representative of full therapeutic doses. The lysis time was shortened in a dose and time-dependent fashion and was clearly distinguishable between doses. Thus, the model appears to be suitable and sensitive to test biosimilarity.

State-of-the-Art Review: Usefulness of Laboratory Techniques for Evaluating Antithrombotic Efficacy of New Therapeutic Strategies

New drugs and new therapeutic strategies are being introduced for the prevention and the management of cardiovascular and thromboembolic disorders. Extensive clinical studies and large-scale epidemiological investigations are conducted to demonstrate the efficacy of these therapeutic approaches. Laboratory assays are invaluable tools for this exploration. We discuss how the new understanding concerning the regulation of the coagulolytic equilibrium offers novel investigation tools. Parameters reflecting the activities of new drugs targeted to their impact site and presenting few side effects are available. In addition to global clotting methods and chromogenic substrate-based assays, introduction of immunoassays has allowed measurement of most of the molecular markers of hemostatic activation. We recommend use of a panel of markers exploring the endothelial damage, the blood cell involvement, the early coagulant pathways' activation (XIIa and VIIa), the thrombin-formation pathways, the fibrin formation, and the evaluation of the global fibrinolytic capacity. When related to the clinical end points, all these laboratory assays offer useful and reliable monitoring of new drugs. They contribute to the establishment of new therapeutic strategies. Key Words: Hemostasis—Activation—Antithrombotic—Therapy— Laboratory monitoring.

Elevated international normalized ratio as a manifestation of post-thrombolytic coagulopathy in acute ischemic stroke

BACKGROUND

A serious complication of intravenous tissue plasminogen activator (tPA) in acute ischemic stroke is hemorrhage. Coagulation factors that may potentially increase the risk of bleeding after tPA are not well understood.

METHODS

We retrospectively reviewed 284 acute ischemic stroke patients who received tPA. Post-tPA coagulopathy was defined as a documented elevation of international normalized ration (INR) > 1.5 within 24 hours after IV tPA without a known cause.

RESULTS

We identified 21 (7.4%) patients with an elevated INR post-thrombolysis. The mean age was 68.3 years (standard deviation ± 11.9) and 57% were male. The mean initial National Institutes of Health Stroke Scale (pre-tPA) was 15.8 (range, 4-35). Liver disease or alcohol abuse was noted in 19%. There were 2 tPA protocol violations who received more than 90 mg tPA. The mean post-tPA INR was 2.03 (range, 1.5-4.7) and the elevation in INR was documented within a mean 5.4 hours (range, 1-15) after tPA initiation. Repeat INR levels returned to normal during their hospital stay in 19 patients. Hypofibrinogenemia was noted in 10 of 12 patients who had fibrinogen levels drawn within 48 hours after tPA initiation and in all 7 patients with fibrinogen levels drawn the same time as the elevated INR. Among the 6 patients with bleeding complications, 2 patients had symptomatic intracerebral hemorrhage.

CONCLUSIONS

We report an under-recognized early transient coagulopathy associated with elevated INR in stroke patients after treatment with tPA.

Pharmacologic reperfusion therapy for acute myocardial infarction

Acute myocardial infarction (MI) remains a significant problem in terms of morbidity, mortality and healthcare costs. Pharmacologic reperfusion therapies for MI are becoming increasingly complex. This review therefore places contemporary pharmacologic MI developments into perspective. An historical overview of pharmacologic reperfusion therapy for MI is provided, followed by an analysis of current limitations, treatment options, and present and likely future pharmacologic therapies. Adjunctive percutaneous and other treatments are also discussed, to clarify what is becoming a rapidly changing field.

Comparison of pharmacokinetics of lanoteplase and alteplase during acute myocardial infarction

OBJECTIVE

Lanoteplase is a rationally designed variant of tissue plasminogen activator. The aim of this study was to examine the pharmacokinetics and functional activity of a single intravenous bolus dose of lanoteplase with those of a bolus plus two-step infusion of alteplase.

DESIGN

Seven-centre substudy of the InTIME-I angiographic trial in patients presenting within 6 hours of onset of suspected acute myocardial infarction.

PATIENTS AND PARTICIPANTS

A total of 31 patients (28 males, 3 females) enrolled in this substudy [mean age 59 (range 26 to 76) years].

METHODS

Twenty-three patients randomised to lanoteplase received single bolus doses of 15 kU/kg (n = 5), 30 kU/kg (n = 3), 60 kU/kg (n = 9), or 120 kU/kg (n = 6). Eight patients received alteplase <or=100mg as a bolus followed by a two-stage 90 min infusion. Blood samples were analysed for antigen concentration and plasminogen activator (PA) activity.

RESULTS

The distribution plasma half-life of approximately 35 min for lanoteplase was at least five times longer than that of alteplase. Lanoteplase plasma clearance averaged 3 L/h (50 ml/min), whereas the mean plasma clearance of approximately 24 L/h (400 ml/min) for alteplase approaches hepatic blood flow following acute myocardial infarction. PA activity after lanoteplase 120 kU/kg remained for 6 hours, compared with less than 4 hours after alteplase 100mg.

CONCLUSIONS

The longer antigen and activity half-lives, slower clearance and less complicated administration of lanoteplase compared with alteplase suggest that it may offer advantages for use as a single intravenous bolus to achieve reperfusion after myocardial infarction.

Effect of reteplase on hemostasis variables: analysis of fibrin specificity, relation to bleeding complications and coronary patency

The first aim of the present study was to characterize the systemic and fibrin-specific lytic effect of reteplase in the treatment of patients with acute myocardial infarction. The second aim was to investigate the relation of hemostasis variables to risk of bleeding complications and to coronary patency. The present study is a hemostatic substudy of the German Recombinant Activator Study. Forty two patients have been treated with 10 MU of reteplase (Group A) and 100 patients with 15 MU of reteplase (Group B), given as a single bolus. Blood samples for assessment of fibrinogen, plasminogen, alpha-2-antiplasmin, fibrinogen degradation products (FDP) and D-dimers were obtained before and at 2, 4, 8, and 24 h after thrombolytic therapy. The median fibrinogen concentration was decreased from 279 to 169 mg/dl in Group A and from 254 to 92 mg/dl in Group B four hours after administration of reteplase. The decrease in fibrinogen was significantly more pronounced in Group B (P=0.0004). The median plasminogen concentration was decreased to 53% in Group A and to 33% in Group B two hours after administration of reteplase (P=0.0001). Alpha-2-antiplasmin was reduced to 27% and 17,5%, respectively (P=0.0007). D-Dimer levels were increased to 5.2 microg/ml in Group A and 11,6 microg/ml in Group B (P=0.02) and FDP levels to 3.0 microg/ml in Group A and 12,6 microg/ml in Group B (P=0.04). Patients with bleeding complications revealed significant lower nadir levels of fibrinogen than patients without bleeding complications (54 mg/dl versus 125.5 mg/dl, P=0.02). There was no significant difference in any hemostatic parameter between patients with patent and nonpatent infarct related arteries.

CONCLUSIONS

Reteplase causes a moderate systemic lytic effect comparable with other relative fibrin specific thrombolytic agents. An increase in the dose from 10 to 15 MU is associated with a marked increase in both fibrin specific and systemic lytic effect. Patients with bleeding complications reveal significant lower nadir levels of fibrinogen than patients without bleeding complications. Determination of any hemostatic parameter seems to be no useful method to predict efficacy of thrombolysis in terms of coronary patency in the individual patient.

Effects of liver blood flow on the pharmacokinetics of tissue-type plasminogen activator (alteplase) during thrombolysis in patients with acute myocardial infarction

BACKGROUND

The removal of recombinant tissue-type plasminogen activator (rt-PA; alteplase) by the liver is so rapid that liver blood flow becomes rate determining for its clearance. In patients with myocardial infarction changes in liver blood flow may result from impaired cardiac performance or drug treatment.

OBJECTIVE

To estimate the effect of variations in liver blood flow on t-PA plasma concentrations during thrombolytic therapy.

METHODS

Fifteen patients with acute myocardial infarction were investigated in an open single-center study at the coronary care unit of University Hospital Leiden. Patients received thrombolytic treatment with 100 mg rt-PA over 3 hours. Liver blood flow was estimated by indocyanine green clearance and by Doppler echocardiography. Concentrations of t-PA antigen, t-PA activity, indocyanine green, alpha 2-antiplasmin, fibrinogen, and fibrin and fibrinogen degradation products were measured.

RESULTS

Indocyanine green clearance and clearance of both t-PA antigen (r = 0.78; p < 0:01) and t-PA activity (r = 0.54; p < 0.05) were significantly related. Significant associations between t-PA antigen and fibrin and fibrinogen degradation products and between t-PA antigen and alpha 2-antiplasmin were also found.

CONCLUSIONS

The liver blood flow of patients with myocardial infarction is inversely correlated with plasma concentrations of t-PA. In patients with severely impaired liver blood flow and heart failure, high t-PA plasma concentrations may occur if standard doses are given. This finding could contribute to optimization of the dosage of t-PA in certain patient groups.

Thrombolytic therapy and proteolysis of factor V

OBJECTIVES

We sought to determine the extent of Factor V proteolysis during thrombolytic therapy.

BACKGROUND

Thrombin- or Factor Xa-activated Factor V is an essential cofactor in the prothrombinase complex. In purified systems, plasmin, the major product of thrombolytic therapy, is known to first activate then inactivate Factor V.

METHODS

We used quantitative gel electrophoresis and Western blotting to analyze the cleavages in plasma Factor V after thrombolytic therapy.

RESULTS

The addition of streptokinase to plasma resulted in the activation then inactivation of Factor V, confirming previous results using purified reagents. We also identified the Factor V fragments resulting from the action of thrombin and plasmin. After thrombolytic therapy, there was considerable Factor V cleavage. The cleavage patterns were consistent with the action of plasmin, with little evidence for the action of thrombin. In the Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries trial (n = 17), we observed an average 58% loss of intact Factor V at 6 h (range 1% to 91%). Samples from the Thrombolysis in Myocardial Infarction trial, Phase II (n = 12), collected on a shorter time scale, showed a loss of up to 99% at 50 min, with the loss of intact Factor V associated with the plasma concentration of plasminogen activator. Samples from patients with bleeding (n = 12) showed extensive Factor V cleavage.

CONCLUSIONS

Factor V cleavage in thrombolytic therapy is primarily plasmin mediated, rapid and often extensive. It is likely that transient increases, as well as longer term losses, of Factor V cofactor activity play a role in both ischemic and hemorrhagic events subsequent to thrombolytic therapy. The extensive loss of Factor V in some patients may affect the estimation of heparinization.

Effects of increased liver blood flow on the kinetics and dynamics of recombinant tissue-type plasminogen activator

OBJECTIVE

To investigate the influence of increased liver blood flow on the pharmacokinetics and pharmacodynamics of recombinant tissue-type plasminogen activator (rt-PA) and to study the changes in endogenous urokinase-type plasminogen activator (u-PA).

METHODS

This open, randomized, crossover trial was carried out in a clinical research unit. Eight healthy, nonsmoking volunteers received linear infusions of 24 mg rt-PA and 92 mg indocyanine green over 160 minutes. Sixty minutes after the infusions were started, the subjects consumed a standardized meal to increase liver blood flow on one occasion and abstained from taking food on the other occasion. Plasma concentrations of indocyanine green, tissue-type plasminogen activator (t-PA) antigen, t-PA activity, total u-PA antigen, plasmin-activatable single-chain u-PA (scu-PA), active two-chain u-PA (tcu-PA), fibrinogen, total fibrin, and fibrinogen/fibrin degradation products (TDP), and alpha 2-antiplasmin were measured.

RESULTS

After the consumption of the meal, the area under the curve (AUC) was 35% (95% confidence interval [CI]: 25%, 43%) lower for indocyanine green, 15% (CI: 6%, 24%) lower for t-PA antigen, and 11% (CI: 2%, 19%) lower for t-PA activity compared to the AUC after subjects abstained from food. No changes were observed in fibrinogen, TDP, or alpha 2-antiplasmin concentrations that were attributable to the intake of food. The infusion of rt-PA caused a fivefold increase in the concentration of active tcu-PA and a concomitant decrease in scu-PA concentrations by more than 50%.

CONCLUSIONS

Increased liver blood flow results in an increase in t-PA clearance. The conversion of the inactive zymogen scu-PA to the active tcu-PA is increased by an infusion of rt-PA, but total u-PA antigen concentrations remain unchanged.

Use of an active center-directed plasmin inhibitor elucidates the multiplicity of plasmin actions

In our studies, designed to synthesize an active center-directed plasmin (PL) inhibitor, N-(4-aminomethylbenzoyl)-4-(3-picolyloxy)-L-phenylalanine n-hexylamide dihydrochloride (PASI-535) was found. We characterized PASI-535 and analyzed the actions of PL, comparing with those of PASI-535 and tranexamic acid (t-AMCHA). (1) PASI-535 strongly inhibited not only fibrinolysis (IC50: 2.9 x 10(-6) M) but also amidolysis (Ki value: 2.9 x 10(-6) M) and fibrinogenolysis (IC50: 4.5 x 10(-6) M) induced by PL. While t-AMCHA which strongly inhibited fibrinolysis (IC50: 6.0 x 10(-5) M), rarely inhibited amidolysis (Ki value: 4.0 x 10(-2) M) and fibrinogenolysis (IC50: 1.0 x 10(-2) M). (2) PL is able to liberate kinins by degrading kininogen. This kinin-generation by PL was inhibited by 2 x 10(-5) M PASI-535. However, it was little inhibited even by 1 x 10(-3) M t-AMCHA. (3) The inhibitory effect of PASI-535 and t-AMCHA on tumor growth was studied. In sarcoma-180 bearing mice, ascites retention and the increase of tumor cells were markedly suppressed by subcutaneous injection of PASI-535, either 30 mg/kg/day or 50 mg/kg/day, for 5 days, and the inhibitory effect was dose-dependent. Although t-AMCHA also reduced both ascites retention and the increase of tumor cells, it needed approximately 40 times (2 g/kg/day) the amount of PASI-535 to exert these effects. PASI-535 may be a useful tool in analyzing the multiplicity of PL actions. Moreover, PASI-535 can be used as an antifibrinolytic drug which has a mechanism of function different from that of t-AMCHA.

Changes in Fibrinogen After rt-PA Administration

Among patients participating in the TIMI-II protocol, there was a variability in the fibrinolytic re sponse to recombinant tissue plasminogen activator (rt- PA). A cohort of 20 TIMI-II patients was selected for detailed study because their responses to rt-PA varied widely in the degree of fibrin(ogen)olysis. Patient plasmas were analyzed by immunoblotting for changes in fibrino gen and plasminogen. Measurements of fibrinogen, fibrin ogen degradation product (FDP), D-dimer, Bβ 1-42, plas minogen, and t-PA were also correlated. Three patterns of response to rt-PA were identified: Group A ( n = 4) had fibrinogenolysis without fibrinolysis; Group B ( n = 11) had fibrinolysis and mild fibrinogenolysis; and Group C ( n = 5) had fibrinolysis with intense fibrinogenolysis. Group C patients also demonstrated qualitative changes in high- molecular-weight (HMW) and low-molecular-weight (LMW) fibrinogens, whereas Group A and B patients demonstrated only mild alterations in fibrinogen compo sition. Plasmin-inhibitor complexes were identified in all three groups. All patients had both plasmin-α2-anti plasmin and plasmin-α2-macroglobulin complexes at the 50-min time point. The concentration of pretreatment plasminogen correlated with the degree of fibrinogenoly sis.

Comparison of the bleeding potential of vampire bat salivary plasminogen activator versus tissue plasminogen activator in an experimental rabbit model

BACKGROUND

Vampire bat salivary plasminogen activator (Bat-PA) has significantly greater fibrin specificity than any of the fibrinolytic agents currently in clinical use. This study tests the hypothesis that avoiding fibrinogen depletion may protect against the hemorrhage induced by plasminogen activator treatment.

METHODS AND RESULTS

Bat-PA was compared with tissue-type plasminogen activator (TPA) in a randomized, prospective, and blinded study using a rabbit ear puncture model of fibrinolytic bleeding. The two agents were used at equimolar dosages (42 nmol/kg) that yielded similar thrombolytic efficacies in a rabbit femoral artery thrombosis model. Both Bat-PA and TPA prolong primary bleeding to double the baseline values, from between 2.1 and 2.3 minutes to between 4.8 and 5.2 minutes. Rebleeding from hemostatically stable sites during the 3-hour observation period occurred equally often with Bat-PA and TPA, 31% from preinjection sites and 23% to 25% from postinjection sites. The lag time between the time of plasminogen activator injection and the onset of rebleeding was likewise the same for both agents, most occurring at 41 to 57 minutes. However, a greater number of prolonged primary or rebleeding occurrences continued for longer than 10 minutes (63% versus 36%) or longer than 30 minutes (30% versus 10%) after Bat-PA than TPA injection. Animals treated with TPA showed a dramatic decrease in plasma fibrinogen and factor VIII concentrations, but those in the Bat-PA treatment group showed only a slight decrease from control values.

CONCLUSIONS

The results indicate that fibrinolytic bleeding after plasminogen activator infusion into rabbits did not correlate with the intensity of the plasma proteolytic state. If anything, Bat-PA usage was associated with a higher proportion of more protracted fibrinolytic bleeding episodes, despite the relatively mild lytic state in comparison with that induced by TPA.

Thrombolytic therapy. Agents, indications, and laboratory monitoring

The patient must be educated to seek medical attention promptly when this malady strikes, and the physician must likewise be taught to institute this therapy as soon as the patient is seen. Less than 6 years ago, it was strongly expressed that there was no rationale for attempting to restore blood flow in the coronary arteries in the setting of myocardial infarction. It was believed that once the diagnosis of myocardial infarction was made, it was too late to relieve myocardial fibers and avert myocyte necrosis. If this thinking and advice of "the damage has already occurred" and "it is too late" prevailed, it would not be known today that treatment of myocardial infarction with thrombolytic therapy within 6 hours of onset of symptoms significantly reduces mortality in comparison with optimal medical treatment (including heparin) without thrombolytic therapy. The concept of thrombolytic therapy is correct. Persistent investigative work in this area will result in better thrombolytic agents and greater dexterity in their use. The thrombolytic agents available today are good, and they can be used safely. To state that agents that have been established to be capable of thrombus resolution should not be used in the treatment of thrombosis is a true example of how not to proceed toward improvement. To be content to remain in the past will not permit entrance into the future.

Use of angioplasty in the management of complicated perioperative infarction following bypass surgery

Ischemic complications in the perioperative period following bypass surgery adversely affect both short- and long-term prognosis. Coronary angioplasty was successfully performed in 2 patients sustaining complicated postoperative myocardial infarctions with resolution of angina and restoration of hemodynamic stability. These cases illustrate that angioplasty can be done safely in such patients and may favorably alter short-term outcome.

Spontaneous splenic rupture complicating anticoagulant or thrombolytic therapy

PURPOSE

To characterize the clinical course and outcomes of reported cases of splenic hemorrhage during thrombolytic or anticoagulant therapy.

METHODS

The Medline, EMBASE (Excerpta Medica), BIOSIS, and SCISEARCH databases for English and foreign literature between 1966 and 1991 were searched. All reports of patients with documented splenic hemorrhage during anticoagulant therapy or thrombolytic therapy were reviewed. Foreign language manuscripts were translated into English.

RESULTS

Seventeen cases of splenic hemorrhage associated with anticoagulant or thrombolytic therapy were found. In one case, there was minor antecedent trauma; in the remaining cases, hemorrhage was spontaneous. Mortality overall was 24% and was more likely in patients with splenic hemorrhage after thrombolytic therapy (50%) than in patients receiving long-term anticoagulants (9%). Splenectomy was performed in 12 of 13 survivors.

CONCLUSIONS

Splenic hemorrhage associated with anticoagulant or thrombolytic therapy is a rare entity. It may be lethal, especially when associated with lytic therapy. Reversal of the anticoagulated or lytic state and emergent splenectomy are the treatment of choice. Splenic hemorrhage can mimic acute myocardial infarction and cardiogenic shock and must be considered when the condition of cardiac patients receiving lytic or anticoagulant drugs suddenly deteriorates.

Alpha 2-antiplasmin supplementation inhibits tissue plasminogen activator-induced fibrinogenolysis and bleeding with little effect on thrombolysis

Tissue plasminogen activator (t-PA) causes fibrinogen proteolysis when alpha 2-antiplasmin levels fall, and this may contribute to t-PA-induced hemorrhage. Because clot-bound plasmin is protected from alpha 2-antiplasmin inhibition, we tested the possibility that alpha 2-antiplasmin supplementation would block t-PA-induced fibrinogenolysis and bleeding without affecting thrombolysis. When added to human or rabbit plasma, alpha 2-antiplasmin inhibits t-PA-induced fibrinogenolysis, but hat little effect on the lysis of 125I-fibrin clots. To examine its effect in vivo, rabbits with preformed 125I-labeled-jugular vein thrombi were randomized to receive t-PA, t-PA and alpha 2-antiplasmin, or saline. alpha 2-Antiplasmin infusion produced a modest decrease in t-PA-induced thrombolysis (from 40.2% to 30.1%, P = 0.12), but reduced fibrinogen consumption from 87% to 27% (P = 0.0001), and decreased blood loss from standardized ear incisions from 5,594 to 656 microliter (P < 0.0001). We hypothesize that alpha 2-antiplasmin limits t-PA-induced hemorrhage by inhibiting fibrinogenolysis and subsequent fragment X formation because (a) SDS-PAGE and immunoblot analysis indicate less fragment X formation in alpha 2-antiplasmin treated animals, and (b) when added to a solution of fibrinogen and plasminogen clotted with thrombin in the presence of t-PA, fragment X shortens the lysis time in a concentration-dependent fashion. These findings suggest that fragment X incorporation into hemostatic plugs contributes to t-PA-induced bleeding. By blocking t-PA-mediated fibrinogenolysis, alpha 2-antiplasmin supplementation may improve the safety of fibrin-specific plasminogen activators.

"Brain attack": an indication for thrombolysis?

OBJECTIVE

The primary objective of this article is to introduce the reader to the use of thrombolytics in the acute treatment of ischemic stroke. Theory and experimental evidence to support this approach are emphasized in addition to potential adverse effects of thrombolysis.

DATA SOURCES

A MEDLINE search was used to identify pertinent literature, including reviews.

STUDY SELECTION

Studies were selected for detailed review if they involved stroke patients and addressed possible toxicities of therapy. Any abstracts concerning ongoing clinical trials also were reviewed.

DATA EXTRACTION

Data from animal investigations using tissue plasminogen activator for the acute treatment of several models of cerebral ischemia were used to support the importance of early treatment (within six hours of symptom onset). Also, studies performed in animal models of stroke revealed that thrombolysis could be accomplished safely in acute ischemic stroke. All human studies published to data are anecdotal case reports, but point to the safety of thrombolysis if administered early. Reviews of ongoing multicenter trials are taken from published abstracts and proceedings.

DATA SYNTHESIS

Thrombolysis holds promise as a hyperacute therapy for acute stroke; however, the risk of intracerebral hemorrhage remains. Crucial to the success of this and any other therapy for acute stroke is the ability to treat patients within hours of symptom onset. Also, the importance of concomitant medications such as heparin and aspirin has not yet been addressed.

CONCLUSIONS

Pharmacists need to be knowledgeable of new treatments of stroke and the risks associated with them. As patient educators, pharmacists can contribute to public awareness by promoting the early recognition of stroke symptoms. As pharmacotherapists, pharmacists need to understand the risks and the important monitoring parameters related to thrombolysis. The results of ongoing multicenter clinical trials are awaited before making a final judgment on the usefulness of thrombolysis in acute ischemic stroke.

Experience with low-dose intracoronary recombinant tissue-type plasminogen activator for nonacute total occlusions before percutaneous transluminal coronary angioplasty

The primary success rate for angioplasty of total occlusions is significantly worse than for subtotal lesions. Pharmacologic recanalization of total occlusions before angioplasty has the potential to improve the primary success rate. To determine the ability of recombinant tissue-type plasminogen activator (rt-PA) to recanalize occlusive thrombi before elective percutaneous transluminal coronary angioplasty, 12 patients with total occlusions, 100% obstruction and Thrombolysis in Myocardial Infarction (TIMI) grade 0 flow, and 5 with functional total occlusions, severe stenoses and TIMI grade 1 flow received an intracoronary infusion of rt-PA. The first 10 patients received 0.2 mg/min for 90 minutes, and the next 7 patients received 0.4 mg/min for 60 minutes. Flow improved by greater than or equal to 1 TIMI grade in 11 patients. Mean TIMI flow improved from 0.3 +/- 0.5 to 1.5 +/- 1.2 (p less than 0.0001). There was a significant improvement in severity of stenosis after rt-PA infusion by both digital caliper (99 +/- 2 vs 84 +/- 16%; p less than 0.0001) and quantitative videodensitometric area assessment (99 +/- 3 vs 94 +/- 6%; p less than 0.004). Angioplasty was successful in 16 of 17 patients (94%). There were 2 out-of-laboratory abrupt closures at 4 days; both were medically treated and 1 had a small myocardial infarction. Only 1 patient had a bleeding complication significant enough to need a transfusion. It is concluded that low-dose intracoronary rt-PA is effective at lysing thrombi less than 3 weeks old. This approach warrants further investigation since it may significantly improve the primary success rate of percutaneous transluminal coronary angioplasty in patients with occlusive thrombus.

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.

Soluble fibrin degradation products potentiate tissue plasminogen activator-induced fibrinogen proteolysis

Despite its affinity for fibrin, tissue plasminogen activator (t-PA) administration causes systemic fibrinogenolysis. To investigate the mechanism, t-PA was incubated with plasma in the presence or absence of a fibrin clot, and the extent of fibrinogenolysis was determined by measuring B beta 1-42. In the presence of fibrin, there is a 21-fold increase in B beta 1-42 levels. The potentiation of fibrinogenolysis in the presence of fibrin is mediated by soluble fibrin degradation products because (a) the extent of t-PA induced fibrinogenolysis and clot lysis are directly related, (b) once clot lysis has been initiated, fibrinogenolysis continues even after the clot is removed, and (c) lysates of cross-linked fibrin clots potentiate t-PA-mediated fibrinogenolysis. Fibrin degradation products stimulate fibrinogenolysis by binding t-PA and plasminogen because approximately 70% of the labeled material in the clot lysates binds to both t-PA- and plasminogen-Sepharose, and only the bound fractions have potentiating activity. The binding site for t-PA and plasminogen is on the E domain because characterization of the potentiating fragments using gel filtration followed by PAGE and immunoblotting indicates that the major species is (DD)E complex, whereas minor components include high-molecular weight derivatives containing the (DD)E complex and fragment E. In contrast, D-dimer is the predominant species found in the fractions that do not bind to the adsorbants, and it has no potentiating activity. Thus, soluble products of t-PA-induced lysis of cross-linked fibrin potentiate t-PA-mediated fibrinogenolysis by providing a surface for t-PA and plasminogen binding thereby promoting plasmin generation. The occurrence of this phenomenon after therapeutic thrombolysis may explain the limited clot selectivity of t-PA.

Thrombolytic versus fibrinogenolytic activity of rt-PA and streptokinase in patients with acute myocardial infarction

In this study the concentration of plasma breakdown products of cross-linked fibrin (XDP), serum fibrinogen-fibrin degradation products (FDP), and plasma fibrinogen were measured before and at the end of the administration of single-chain recombinant tissue-type plasminogen activator (rt-PA, 100 mg IV over three hours) or streptokinase (1.5 million units over one hour), respectively, in two groups, each composed of 22 patients with acute myocardial infarction. The XDP concentration was not statistically different between the two groups at the end of thrombolytic treatment, whereas FDP and fibrinogen concentrations were significantly different (FDP: streptokinase 396 +/- 287 vs rt-PA 177 +/- 222 micrograms/mL, p less than 0.01; fibrinogen: streptokinase 71 +/- 43 vs rt-PA 181 +/- 49 mg/dL, p less than 0.001). These results indicate that the two drugs have equipotent thrombolytic activity at this administration regimen but that rt-PA causes a markedly more selective lysis of fibrin in comparison with streptokinase.

Quantitation of venous clot lysis with the D-dimer immunoassay during fibrinolytic therapy requires correction for soluble fibrin degradation

Plasma cross-linked fibrin-degradation products were analyzed using a D-dimer (DD) immunoassay in patients with deep vein thrombosis (DVT) or acute myocardial infarction (MI) treated with fibrinolytic therapy, and the results were correlated with clot lysis documented angiographically. In 13 patients with DVT, the mean DD concentration increased 10-fold (1,074 +/- 252 to 10,333 +/- 1,004 ng/ml) during therapy, but neither the peak level nor the DD concentration integrated over the course of therapy correlated with clot lysis. Since plasma DD can derive from degradation of soluble plasma fibrin as well as from thrombi, the contribution of the former was estimated by in vitro incubation of the pretreatment plasma with plasminogen activator. Subtraction of this value from the measured posttreatment DD concentration provided a "corrected" level that represented DD originating from lysis of thrombi. This modification resulted in improved correlation of DD levels with clot lysis. The mean corrected peak DD was higher in patients with successful thrombolysis (8,780 +/- 1,352 ng/ml) compared with patients without lysis (3,075 +/- 589 ng/ml, p less than 0.001). There was a moderate correlation between the volume of clot lysed and the corrected peak DD (r = 0.62) and a higher correlation with the corrected DD integrated over the course of treatment (r = 0.97). By contrast, the corrected DD concentrations were near zero in patients treated for MI with or without thrombolytic reperfusion, suggesting that fibrin in small coronary thrombi did not contribute significantly to total plasma DD during therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Improved infarct-related arterial patency after high dose, weight-adjusted, rapid infusion of tissue-type plasminogen activator in myocardial infarction: results of a multicenter randomized trial of two dosage regimens

To determine whether a weight-adjusted high dose (2 mg/kg body weight over 3 h) rapid infusion of recombinant tissue-type plasminogen activator (rt-PA) was more efficacious than a weight-adjusted standard dose (1.25 mg/kg over 3 h) in achieving reperfusion in the setting of acute myocardial infarction, 175 patients were entered into a randomized multicenter trial. Eighty-four patients were entered into the high dose group, receiving 1.2 mg/kg (10% given as a bolus injection) over 1 h, followed by 0.8 mg/kg over the next 2 h. Ninety-one patients were given 0.75 mg/kg (10% given as a bolus injection) in 1 h, followed by 0.5 mg/kg administered over the next 2 h. The median dose in the group that received 2 mg/kg dose was 145 mg, compared with 100 mg in the group that received 1.25 mg/kg. The 90 min patency rate in the group that received 2 mg/kg was 84% compared with 70% in the group that received 1.25 mg/kg (p = 0.003). Sixty-four percent of the patients in each group underwent coronary angioplasty at the time of cardiac catheterization. The infarct-related artery patency rate at the end of catheterization was 91% in the group that received 2 mg/kg compared with 83% in the group that received 1.25 mg/kg (p = 0.08). Among patients with a patent infarct-related coronary artery after catheterization, the 6 month mortality rate in the group that received 2 mg/kg was 2.9% compared with 9.8% in the group that received 1.25 mg/kg (p = 0.15). The bleeding complication rate in the two groups was similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of selective endoperoxide/thromboxane A2 receptor antagonism with sulotroban on tPA-induced thrombolysis in a rabbit model of femoral arterial thrombosis

The thrombolytic efficacy of recombinant tissue-type plasminogen activator (tPA) in the presence and absence of the selective endoperoxide/thromboxane A2 (TXA2) receptor antagonist, sulotroban (BM 13.177, SK&F 95587) was studied in a model of femoral artery thrombosis in the anesthetized rabbit. The thrombus was formed by injection of thrombin, CaCl2 and whole blood into an isolated segment of the femoral artery. After 30 min of stable thrombotic occlusion of the femoral artery, tPA was infused IV for 90 min at doses of 5.0, 7.5 and 10.0 micrograms/kg/min. In other experiments, sulotroban was administered as a bolus dose of 1 mg/kg/IV, followed by a constant infusion of 1 mg/kg/hr concurrent with tPA infusion. Sulotroban had no effect on the incidence of tPA-induced reperfusion at any dose studied or on residual clot weight. However, at a tPA dose of 10 micrograms/kg/min, IV lysis time was reduced in sulotroban treated animals from 65 min to 29 min (P less than 0.05), and the magnitude of femoral artery blood flow achieved as a result of tPA-induced reperfusion was greater in sulotroban-treated animals. These data suggest that adjunctive therapy with a selective endoperoxide/TXA2 antagonist improves the response to tPA when tPA is administered at a maximal or near maximally effective pharmacological dose.

Pharmacodynamics of thrombolysis with recombinant tissue-type plasminogen activator. Correlation with characteristics of and clinical outcomes in patients with acute myocardial infarction. The TAMI Study Group

Coagulation analysis was performed on blood samples from 386 patients with acute myocardial infarction drawn before, during, and after a continuous intravenous infusion of 150 mg recombinant tissue-type plasminogen activator (rt-PA) (Activase). Plasma rt-PA rose to peak levels of 2.1 +/- 3.1 micrograms/ml (mean +/- SD). Fibrinogen levels measured by coagulation rate and by sulfite precipitation decreased from baseline levels of 3.0 +/- 0.9 and 3.2 +/- 1.0 g/l, respectively, to nadir levels of 1.4 +/- 0.75 and 1.8 +/- 0.92 g/l, respectively, and were associated with peak levels in serum of fibrinogen-degradation products (FDP) of 230 +/- 470 micrograms/ml. Forty percent of patients experienced a nadir functional-fibrinogen level of less than 1.0 g/l, whereas 20% fell below 0.5 g/l. Nadir fibrinogen levels did not correlate with patency of the infarct-related coronary artery at 90 minutes or with risk of coronary vessel reocclusion within 7-10 days. However, the risk of coronary artery reocclusion was inversely related to the baseline functional fibrinogen level (p = 0.0008), with the magnitude of its drop to nadir level (p = 0.0003) as well as to peak levels of FDP (p = 0.038). Quantitative blood loss correlated with all markers for systemic fibrinogenolysis including nadir fibrinogen level (r = -0.20, p = 0.0011), percent decrease of fibrinogen (r = 0.22, p = 0.001), and peak FDP levels (r = 0.14, p = 0.020). Both patients who experienced intracranial hemorrhage presented with high baseline fibrinogen levels and experienced extensive degradation of coagulable fibrinogen. Overall, patients at greatest risk of systemic fibrinogenolysis tended to be relatively older women with lower body weight.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased immunoreactivity of plasma after fibrinolytic activation in an anti-DD ELISA system. Role of soluble crosslinked fibrin polymers

After addition of a low concentration of thrombin to normal plasma, a progressive and significant increase in crosslinked fibrin polymers was found by sodium dodecyl sulfate agarose gel electrophoresis, reaching 27% of total fibrinogen and fibrin before gel formation. As measured by enzyme-linked immunosorbent assay with a monoclonal antibody specific for an epitope near the gamma gamma crosslink site, increased immunoreactivity of plasma did not occur after adding thrombin despite formation of crosslinked fibrin polymers, which indicates that the antibody does not recognize the epitope in the polymers. Addition of tissue-type plasminogen activator (t-PA) to plasma resulted in a more rapid degradation of fibrin polymers than of fibrinogen, indicating that the fibrin specificity of t-PA is retained with soluble fibrin. Coincident with degradation of plasma crosslinked fibrin polymers, plasma DD immunoreactivity increased 70-fold from 50.3 +/- 4.5 (mean +/- SD) to 3,560 +/- 1,235 ng/ml. The presence of increased crosslinked fibrin polymers produced by adding thrombin to plasma significantly increased maximum immunoreactivity after t-PA-induced degradation to 18,500 +/- 11,780 ng/ml. The increase in DD immunoreactivity was dependent on t-PA concentration; no elevation occurred below 0.01 micrograms/ml, and maximal increases occurred above 100 micrograms/ml. Analysis of gel electrophoretic patterns of thrombin and t-PA-treated plasma samples suggests that the DD reactivity of t-PA-treated plasma is mainly due to degradation of soluble crosslinked fibrin polymers. Our findings indicate that plasmic degradation of soluble fibrin polymers in plasma may be an important source of fragment DD during thrombolytic therapy.

The effects of a new tissue plasminogen activator analogue, Fb-Fb-CF, on cerebral reperfusion in a rabbit embolic stroke model

Early fibrinolytic therapy with full molecular tissue plasminogen activator (t-PA) has been observed to be both angiographically and clinically effective when employed in animal stroke models. Preliminary clinical trials with t-PA are in progress. It is possible to refine t-PA by developing fragments or analogues of the drug. Using recombinant DNA technology in the Escherichia coli system, a t-PA analogue consisting of the catalytic fragment of t-PA and a dimer of the B fragment of staphylococcal protein A (Fb-Fb-CF) has been produced. Because this analogue has a long serum half-life of 90 minutes, we employed Fb-Fb-CF in a rabbit cerebral embolic stroke model to assess its efficacy as a reperfusion agent. When given as a bolus to 10 animals 15 minutes after embolization, Fb-Fb-CF produced angiographic cerebral reperfusion in 48 +/- 21 minutes (+/- SD), while in 8 saline-treated controls, reperfusion was not observed at 180 minutes in any animal (p less than 0.01). In another experiment reperfusion was demonstrated at 66 +/- 32 minutes in 11 animals treated with Fb-Fb-CF 90 minutes after embolization as compared with 100 +/- 25 minutes in 12 saline-treated controls (p less than 0.01). A small macroscopic hemorrhage within an infarct was seen in 1 Fb-Fb-CF-treated animal in the 15-minute experiment and in none of the controls. In the 90-minute experiment, macroscopic hemorrhagic infarction was seen in 4 Fb-Fb-CF-treated animals and in 3 controls.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

Effect of thromboxane synthase inhibition on the thrombolytic action of tissue-type plasminogen activator in a rabbit model of peripheral arterial thrombosis

The thrombolytic efficacy of recombinant tissue-type plasminogen activator (tPA) in the presence and absence of a thromboxane synthase inhibitor was studied in a model of femoral artery thrombosis in the anesthetized rabbit. The thrombus was formed by injection of thrombin and whole blood into an isolated segment of the femoral artery. After 30 min of stable thrombotic occlusion of the femoral artery, sodium heparin (300 U/kg, i.v.) was administered and tPA was infused locally to the site of the thrombus for 30 min at 0.01, 0.10 or 1.0 microgram/kg/min. In other experiments, CGS 13080, a selective thromboxane synthase inhibitor, was administered at a dose of 2 mg/kg i.v., 5 min before tPA was infused and at the end of the 30 min tPA infusion. Pretreatment with CGS 13080 resulted in a shorter time to tPA-induced reperfusion, greater incidence of reperfusion and increased the magnitude of femoral artery blood flow achieved after effective thrombolysis. Furthermore, pretreatment with CGS 13080 resulted in a greater than 10-fold enhancement in the effective dose of tPA. These data indicate that thromboxane synthase inhibition may be beneficial as an adjunct to thrombolytic therapy with tPA.

Human tissue-type plasminogen activator releases fibrinopeptides A and B from fibrinogen

In five patients with venous thromboembolic disease treated with recombinant tissue-type plasminogen activator (rt-PA), there was a marked increase in the mean concentrations of fibrinopeptide A (from 0.6 to 5.9 nM; P less than 0.0001) and desarginine fibrinopeptide B (from 5.6 nM to 24.1 nM; P less than 0.01) 30 min after a bolus of rt-PA (0.6 mg/kg). Thrombin was unlikely to be responsible because the levels of desarginine fibrinopeptide B exceeded those of fibrinopeptide A and the changes occurred despite concomitant heparin therapy. The purpose of this study therefore, was to determine whether rt-PA directly releases the fibrinopeptides from fibrinogen. Incubation of rt-PA with heparinized plasma or purified fibrinogen resulted in time and dose-dependent release of both fibrinopeptide A and B. Contaminating thrombin was not responsible for this activity by the following criteria: the rate of rt-PA mediated fibrinopeptide B release was considerably faster than that of fibrinopeptide A, and fibrinopeptide release was unaffected by heparin, hirudin, or a monospecific antithrombin IgG. Aprotinin also had no effect on fibrinopeptide release, indicating that this activity was not plasmin mediated. Fibrinopeptide release was shown to be due to rt-PA because this activity was completely blocked by a monoclonal antibody against the enzyme. Further, the specificity of rt-PA for the thrombin cleavage sites on fibrinogen was confirmed by the demonstration that rt-PA released fibrinopeptide A or fibrinopeptide B from fibrinopeptide A or B-containing substrates, respectively. These studies thus demonstrate that (a) rt-PA releases fibrinopeptides A and B from fibrinogen thereby indicating that this enzyme is not specific for plasminogen, and (b) plasma fibrinopeptide A and desarginine fibrinopeptide B levels are not specific markers of thrombin action on fibrinogen in patients receiving rt-PA.

Comparison of two dose regimens of intravenous tissue plasminogen activator for acute myocardial infarction

Two dosing schedules of intravenous tissue plasminogen activator (t-PA) for acute myocardial infarction were compared in a multicenter trial. At 2.95 +/- 1.1 hours from onset of chest pain, 386 patients received 150 mg of intravenous t-PA. For the first 178 patients (group A), 60 mg were given in the first-hour dose and the remaining 90 mg were infused over 7 hours. In the subsequent 208 patients (group B), the first-hour dose was 1.0 mg/kg and the remaining 150 mg were given over 5 hours. At initial angiography 94 +/- 30 minutes into therapy, the infarct vessel patency was 64% in group A versus 75% in group B (p = 0.02). By final angiography with up to 4 selective contrast injections, patency was 68% versus 77%, respectively (p = 0.06). Repeat angiography at 7 to 10 days demonstrated reocclusion in 17% of group A and 13% of group B patients (p = 0.35). There was no difference in fibrinogen nadir or mean hematocrit drop between the 2 groups: 120 mg/dl and 11 points, respectively, in group A compared with 120 mg/dl and 10 points in group B. However, bleeding was reduced in group B patients as evident by a decrease in requirement for greater than or equal to 2 units of packed red blood cell transfusion (group A 36%, group B 27%, p = 0.05) and lower incidence of gastrointestinal bleeding (group A 12%, group B 4%, p = 0.002). To further study the importance of weight adjustment, patients were divided into 2 groups according to weight (less than or equal to 90 kg versus greater than 90 kg).(ABSTRACT TRUNCATED AT 250 WORDS)

Recombinant tissue plasminogen activator to lyse experimentally induced retinal arterial thrombi

We evaluated the efficacy of intravenously administered recombinant tissue plasminogen activator to lyse laser-induced arterial thrombi in the stroke-prone, spontaneously hypertensive rat model. The arterial thrombi were confirmed histologically, and assessed by color photographs and fluorescein angiography before and after intravenous tissue plasminogen activator or saline therapy. Experimental animals received tissue plasminogen activator (1 mg/kg of body weight) given intravenously over one hour, and control animals received similar volumes of normal saline. Tissue plasminogen activator was effective in lysing experimental retinal arterial thrombi.

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)

Newer emergency reperfusion techniques in acute myocardial infarction

We have given an overview of the management of the acute myocardial infarction patient utilizing the aggressive reperfusion techniques available today. Anatomic reperfusion rates have been over 95% with the combined methods described. The remaining problems technically are those of earlier reperfusion, methods to enhance myocardial recovery after ischemia, and prevention of restenosis or reocclusion. The use of laser methodology, coronary sinus retroperfusion, partial left heart bypass, and other innovative strategies may improve these results. The introduction of tissue plasminogen activator will affect our approach and will profoundly alter society's expectations of therapeutic success. Still, patients will die from acute myocardial infarction and its complications. The search for a prevention must, therefore, not be overshadowed by our current enthusiasm for reperfusion techniques. Hopefully, our current approach will become a historical footnote as breakthroughs in preventive strategies occur.

Thrombolysis in Myocardial Infarction (TIMI) Trial--phase I: hemorrhagic manifestations and changes in plasma fibrinogen and the fibrinolytic system in patients treated with recombinant tissue plasminogen activator and streptokinase

Two hundred ninety patients with acute myocardial infarction were treated according to random assignment with an intravenous infusion of either 80 mg of recombinant tissue plasminogen activator (rt-PA) over 3 h or 1.5 million units of streptokinase over 1 h. Patients received an intravenous bolus of heparin (5,000 U [USP]) before pretreatment coronary angiography and a continuous infusion (1,000 U/h) starting 3 h later. The frequency of major and minor hemorrhagic events (33% rt-PA, 31% streptokinase) and associated transfusions (22% rt-PA, 20% streptokinase) were comparable in both groups. More than 70% of bleeding episodes in each group occurred at catheterization or vascular puncture sites. Precipitable fibrinogen levels, measured in plasma samples collected in the presence of a protease inhibitor (aprotinin), declined in rt-PA and streptokinase groups by averages of 26 and 57% at 3 h and by 33 and 58% at 5 h, respectively (rt-PA versus streptokinase, p less than 0.001). At 5 h the plasma plasminogen declined by 57% (rt-PA) and 82% (streptokinase) (p less than 0.001); plasma fibrin(ogen) degradation products were higher in streptokinase-treated patients (244 +/- 12 micrograms/ml, mean +/- SE) than in rt-PA-treated patients (97 +/- 9 micrograms/ml, p less than 0.001). At 27 h, plasma fibrinogen and plasminogen levels were lower and fibrin(ogen) degradation products higher than pretreatment levels in both groups. The frequency of hemorrhagic events was higher in patients with greater changes in plasma factors at 5 h; within treatment groups the levels of fibrin(ogen) degradation products correlated with bleeding complications (p less than 0.005). Thus, in the doses administered, rt-PA induces systemic fibrinogenolysis that is substantially less intense than that induced by streptokinase. The high frequency of bleeding encountered is related to the protocol used, including vigorous anticoagulation, arterial punctures and thrombolytic therapy. These findings emphasize the need for avoidance of invasive procedures and for meticulous care in the selection and management of patients subjected to thrombolytic therapy.

Kinetic studies on the effect of heparin and fibrin on plasminogen activators

1. Possible interactions between fibrin(ogen) and heparin in the control of plasminogen activation were studied in model systems using the thrombolytic agents tissue-type plasminogen activator (t-PA), urokinase and streptokinase.plasminogen activator complex and the substrates Glu- and Lys-plasminogen. 2. Both t-PA and urokinase activities were promoted by heparin and by pentosan polysulphate, but not by chondroitin sulphate or hyaluronic acid. The effect was on Km. 3. In the presence of soluble fibrin (and its mimic, CNBr-digested fibrinogen) the effect of heparin on t-PA was attenuated, although not abolished. In studies using a monoclonal antibody and 6-aminohexanoic acid, it was found that heparin and fibrin did not seem to share a binding site on t-PA. 4. The activity of t-PA B-chain was unaffected by heparin, so the binding site is located on the A-chain of t-PA (and urokinase). 5. Fibrin potentiated the activity of heparin on urokinase. The activity of streptokinase.plasminogen was unaffected by heparin whether or not fibrin was present. 6. If these influences of heparin and fibrin also occur in vivo, then, in the presence of heparin, the relative fibrin enhancement of t-PA will be diminished and the likelihood of systemic activation by t-PA is increased.

The preparation and properties of novel reversible polymer-protein conjugates. 2-omega-Methoxypolyethylene (5000) glycoxymethylene-3-methylmaleyl conjugates of plasminogen activators

The preparation of a reagent capable of reversibly attaching polyethylene glycol to proteins and the use of this material in modifying the plasminogen activators urokinase- and tissue-type plasminogen activator are described. The characterisation and the reversible nature of these protein-polymer conjugates are discussed, and some of the in vitro properties of these modified enzymes are explored.

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.

Recombinant human tissue-type plasminogen activator therapy in acute thromboembolic stroke

Systemic fibrinolytic therapy for acute stroke is no longer recommended because of resulting systemic fibrinolysis and the risk of intracerebral hemorrhage. Human tissue-type plasminogen activator (TPA) is a native enzyme that converts plasminogen to plasmin with subsequent clot lysis. The affinity for plasminogen is increased several-fold when the substrate is bound to fibrin. At appropriate dosage, "clot-specific" thrombolysis may be achieved at the surface of the thrombus without creating systemic fibrinolysis. The authors designed a study to evaluate the effect of intravenous TPA administered 2 hours after acute thromboembolic stroke in rats. This time course was chosen to simulate an analogous clinical situation. Middle cerebral artery embolic stroke was caused by intracarotid injection of 0.025 cc of human blood clot in 16 rats. Regional cerebral blood flow, measured by the hydrogen clearance technique, and electroencephalographic (EEG) recordings were obtained every 30 minutes for 5 hours after thromboembolism. Eight rats received a 1-hour infusion of intravenous TPA (1.5 mg/kg) 2 hours after injection of emboli. Ipsilateral blood flow increased significantly within 30 minutes after intravenous TPA and reached preembolic levels within 60 minutes. Blood flow did not improve in the eight control rats throughout the experiment. Power spectral analysis of the EEG recordings showed improvement in the treated group compared to the control group. Postmortem angiography revealed proximal middle cerebral artery occlusion in control animals and patent middle cerebral arteries in TPA-treated animals. Serum fibrinogen and fibrin split products were unchanged in both groups, indicating the absence of systemic fibrinolysis. There were no intracerebral hemorrhages. It is concluded that, in this rat model, TPA increases blood flow with subsequent improvement in the EEG recording after thromboembolic stroke without evidence of systemic fibrinolysis. Intravenous TPA may be useful in the treatment of acute stroke in man.

Tissue plasminogen activator: an evaluation of clinical efficacy in acute myocardial infarction

Recombinant tissue plasminogen activator (t-PA) is a synthetic fibrinolytic protein which activates plasminogen or converts plasminogen to plasmin specifically in the presence of fibrin. With its "clot-selectivity", t-PA is capable of lysing clots without having a significant effect on circulating plasminogen. In contrast, activation by streptokinase and urokinase is non-specific and affects circulating as well as thrombus plasminogen. These agents, therefore, have a greater potential to induce bleeding than does t-PA. Plasma levels of t-PA following intravenous administration are generally proportional to the dose, but there can be significant interpatient variation. The drug is eliminated primarily by hepatic metabolism and is then excreted in the urine. Half-life of circulating t-PA ranges from 2-8 minutes. Most clinical trials of t-PA have evaluated its use in acute myocardial infarction. Indeed, its current indication is for thrombolysis in evolving MI. Short-term benefits of t-PA administration include a prompt reperfusion and restoration of coronary artery patency in patients with total coronary artery occlusion. The degree to which the heart benefits from thrombolysis is unknown, but electrocardiographic changes, changes in cardiac enzymes and alterations in the pattern of chest pain indicate that rapid reperfusion may limit the size of the infarct. Overall, t-PA appears to be a relatively safe thrombolytic agent. Bleeding is the most significant adverse effect reported with t-PA administration. In most cases, however, bleeding has been minor. Other reported adverse effects include reperfusion arrhythmias, bradycardia, and chest pain. Allergic reactions were not observed in clinical trials.