Alteplase: a tissue plasminogen activator for acute myocardial infarction

Bilateral lysis of aortic saddle thrombus with early tissue plasminogen activator (BLASTT): a prospective, randomized, placebo-controlled study in feline acute aortic thromboembolism

OBJECTIVES

The aim of this study was to investigate the impact of tissue plasminogen activator (TPA) on the treatment of feline aortic thromboembolism (FATE).

METHODS

Cats diagnosed with FATE involving ⩾2 limbs were enrolled in a prospective, multicenter, double-blinded, randomized, placebo-controlled study within 6 h of an event. Diagnosis was made by clinical findings and one confirmatory criterion. Cats received placebo or TPA (1 mg/kg/h with the first 10% by bolus). All cats received pain control and thromboprophylaxis. The primary outcome was a change from baseline in a published limb score at 48 h. Secondary outcomes included 48 h survival, survival to discharge and complication proportions. Statistical analyses included pattern-mixture models, logistic regression and Fisher's exact, Student's t- and Mann-Whitney-Wilcoxon tests.

RESULTS

Based on a power analysis, 40 cats were enrolled; however, only 20 survived to 48 h (TPA, n = 12; placebo, n = 8 [P = 0.34]). There was a statistically significant improvement in limb scores compared with baseline for both groups (P <0.001). Limb score at 48 h was 1 point lower (better) in the TPA group (P = 0.19). Thrombolysis had no statistically significant effect on 48 h survival (P = 0.22). Lower affected limb lactate was associated with better 48 h survival (odds ratio 1.53, 95% confidence interval 1.08-2.17; P = 0.02). The survival to discharge rates were 45% (TPA) and 30% (placebo; P = 0.51). Complications in the TPA and placebo groups included acute kidney injury (22% and 19%, respectively; P = 1.00) and/or reperfusion injuries (33% and 19%, respectively; P = 0.45).

CONCLUSIONS AND RELEVANCE

Survival and complication rates of acute FATE were not different with or without thrombolysis. High in-hospital mortality decreased the statistical power to detect a statistically significant difference between treatments with regard to our primary outcome.

Label-Free Kinetic Studies of Hemostasis-Related Biomarkers Including D-Dimer Using Autologous Serum Transfusion

The objective of this study was to evaluate the elimination kinetics of hemostasis-related biomarkers including the prothrombin activation fragment F1+2, thrombin-antithrombin complex (TAT), plasmin-α₂-antiplasmin complex (PAP), and D-dimer in humans. Autologous serum was used as a biomarker source and infused into 15 healthy volunteers. Serum was prepared from whole blood in the presence of recombinant tissue-type plasminogen activator (final concentration 20 μg/mL) to induce plasmin generation required for PAP and D-dimer formation. Serum transfusions (50 mL/30 min) were well tolerated by all subjects. Endogenous thrombin formation was not induced by serum infusions as measured using a highly sensitive oligonucleotide-based enzyme capture assay. Median peak levels (x-fold increase over baseline) of F1+2, TAT, PAP, and D-dimer of 3.7 nmol/L (28.9), 393 ng/mL (189.6), 3,829 ng/mL (7.0), and 13.4 mg/L (34.2) were achieved at the end of serum infusions. During a 48 h lasting follow-up period all biomarkers showed elimination kinetics of a two-compartment model. Median (interquartile range) terminal half-lives were 1.9 (1.3–3.6) h for F1+2, 0.7 (0.7–2.6) h for TAT, and 10.8 (8.8–11.4) h for PAP. With 15.8 (13.1–23.1) h the D-dimer half-life was about twice as long as previously estimated from radiolabeling studies in animals and small numbers of human subjects. The serum approach presented here allows label-free and simultaneous analysis of the elimination kinetics of various hemostasis-related biomarkers. Based on these data changes in biomarker levels could more precisely used to estimate the activity level of the hemostatic system.

Thrombolytic therapy: a review of its use in acute myocardial infarction

OBJECTIVE

To review the literature on the use of thrombolytic agents in the pharmacotherapeutic management of acute myocardial infarction (AMI).

DATA SOURCE

English-language clinical trials, reviews, and editorials derived from MEDLINE (January 1966-September 1997) and/or cross-referencing of selected articles.

STUDY SELECTION

Articles that were selected best represent the clinical trials researching the role for thrombolytics in the therapy of AMI to improve morbidity and mortality.

DATA SYNTHESIS

AMI is one of the leading causes of mortality in the US. Following supportive data that the most common cause of an AMI is an intracoronary thrombus, clinical investigation has demonstrated that intravenous thrombolytic agents improve survival rates in patients who experience an AMI. Several clinical trials have been conducted to determine whether one thrombolytic agent is superior to others with respect to improving mortality. At present, only the first Global Use of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries (GUSTO-I) trial has reported any statistically significant difference in mortality rate. In this trial, "front-loaded" alteplase induced a statistically significant (p < 0.001) 1% absolute reduction in 30-day and 1-year mortality compared with streptokinase. This has led to alteplase being the preferred thrombolytic at many US institutions. However, the results of GUSTO-I have been questioned by some on the basis of either study design or clinical significance.

CONCLUSIONS

Thrombolytic agents have secured a place in the treatment of AMI due to their well-proven reduction in mortality rates. In general, comparative trials have demonstrated minimal differences in efficacy among these agents. Probably just as important as choosing which thrombolytic agent to use is ensuring that a patient experiencing an AMI is administered thrombolytic therapy unless a contraindication to receive such therapy exists in the patient and/or the patient is a candidate to receive an emergent intracoronary procedure. Trials also indicate that the sooner thrombolytics can be administered, the greater the benefit to the patient.

"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.

The role of the endothelium in in vivo anticoagulation

Endothelial cells play an important role in the anticoagulation of circulating blood. They participate in at least four mechanisms that aid in preventing vascular occlusion by platelet plugs or fibrin deposition. These mechanisms include the fibrinolytic pathway, the enhancement of action of endogenous inhibitors of coagulation, the inhibition of cofactors required for fibrin formation, and the synthesis and release of platelet inhibitors. Thus, the endothelium can no longer be viewed merely as a passive barrier separating the blood from the interstitial matrix. Instead, it must be viewed as an active participant in the maintenance of blood fluidity and the prevention of thrombogenesis.

Tissue plasminogen activator for the treatment of thromboembolism in infants and children

We report our experience with the use of tissue plasminogen activator to treat 12 infants and children with various thromboembolic states after conventional thrombolytic agents had failed. The dosage range was between 0.1 to 0.5 mg/kg per hour. Complete clot dissolution occurred in seven cases after 2 hours to 3 days of therapy. Partial clot dissolution and clinical improvement were noted in another four patients. Bleeding complications were noted in 6 of the 12 patients and included bruising, oozing from various venipuncture sites, and bleeding; these complications were controlled by clinically available means. In all cases with bleeding the dose rate was in the higher range (0.46 to 0.50 mg/kg per hour). In one patient, restlessness, agitation, and screaming were noted during administration of tissue plasminogen activator and when it was reinstituted. We conclude that tissue plasminogen activator is effective in inducing clot lysis in children. Because the effective dose appears to overlap with those causing bleeding, we recommend that a dose of 0.1 mg/kg per hour be started and increased gradually if clot dissolution does not occur, with close monitoring for bleeding.

Intracerebral hemorrhage related to cerebral amyloid angiopathy and t-PA treatment

Tissue plasminogen activator (t-PA) has been approved as thrombolytic therapy for the treatment of acute myocardial infarction, but this agent can cause serious bleeding complications including intracerebral hemorrhages. Mechanisms underlying the development of these hemorrhages have not been clarified. We report a patient who developed two intracerebral hemorrhages shortly after receiving t-PA for the treatment of an acute myocardial infarction, and who was found to have cerebral amyloid angiopathy at autopsy. Staining of cortical sections with Congo red and an antibody directed against beta amyloid protein (A4 peptide) disclosed specific involvement of most of the subarachnoid and superficial cortical vessels in the region of the two hemorrhages. Based on the findings in this patient and in 6 additional patients reported recently, it is likely that cerebral amyloid angiopathy plays a pathogenic role in some intracerebral hemorrhages associated with the administration of t-PA. The cautious use of t-PA with heparin in patients who are elderly or demented may be advisable.