Low-Molecular-Weight Heparins in Conjunction with Thrombolysis for ST-Elevation Acute Myocardial Infarction

Efficacy and Safety of Low-Molecular-Weight Heparins As An Adjunct to Thrombolysis in Acute ST-Elevation Myocardial Infarction

A 48-hour course of intravenous unfractionated heparin (UFH) is the standard of treatment in conjunction with fibrin-specific thrombolysis in ST-elevation myocardial infarction (STEMI). In recent trials, the efficacy and safety of in-hospital administration of subcutaneous low-molecular-weight heparins (LMWH), previously proven effective in non-ST-elevation acute coronary syndromes, have been investigated in the setting of STEMI. The aim of this review was to evaluate the available evidence supporting the use of LMWH in STEMI.

Overall, about 27,000 patients treated with various thrombolytic regimens, were included in 12 open-label randomized clinical trials, where dalteparin, reviparin or enoxaparin were administered. While acknowledging the wide variability in study dimensions, designs and end-points, a higher efficacy of LMWH was observed overall as compared to placebo, and also to UFH (mainly as regards the occurrence of reinfarction). As regards safety, bleedings were more frequent than placebo and comparable to UFH in LMWH groups, with the exception of the pre-hospital ASSENT-3 PLUS trial, where in elderly patients, enoxaparin had an incidence of intracranial hemorrhage twice higher than UFH. In a recent double-blind, randomized, mega-trial including over 20,000 patients, the superior efficacy on in-hospital and 30-day adverse cardiac events (namely reinfarction), and comparable safety on intracranial bleedings, of enoxaparin compared to UFH, was shown.

In conclusion, in-hospital subcutaneous administration of dalteparin, reviparin and enoxaparin, as an adjunct to various thrombolytics in STEMI, appears feasible and at least as effective and safe as 48-hour intravenous treatment with UFH. In accordance with the available strongest evidence, an initial intravenous bolus of enoxaparin followed by twice daily subcutaneous administration for about 1 week should be the preferred regimen, and should be strongly considered instead of intravenous UFH. Along with its easiness of use, not requiring laboratory monitoring, subcutaneous administration of LMWH following STEMI treated with thrombolysis allows extended antithrombotic treatment, while permitting early mobilization (and rehabilitation) of patients.

Direct comparison of enoxaparin and nadroparin in a rabbit model of arterial thrombosis prevention

INTRODUCTION

The aim of the study was to evaluate and compare the efficacy of standard unfractionated heparin (UFH) and low-molecular weight heparins (LMWH's).

MATERIALS AND METHODS

We modified a previously published rabbit model of arterial thrombosis prevention [1,2] to compare unfractionated heparin and two different doses of two low-molecular weight heparin fragments--nadroparin and enoxaparin. Thrombosis in the distal aorta was triggered by vessel wall injury and critical stenosis. Blood flow in the damaged arterial segment was monitored by a flow probe placed distal to the constrictor. The primary endpoints of the study were: (1) cumulative flow, (2) time to occlusion and (3) residual clot weight. Thirty six animals were split into 6 groups with six animals in each group. Control groups were given saline or heparin and four more groups were used to compare LMWH's at 2 different doses.

RESULTS

In our study, all treatments were superior to the saline control group (alpha<or=0,01). Standard heparin was inferior (alpha<or=0,05) to both low molecular weight heparins for all primary endpoints (cumulative flow, time to occlusion and residual clot weight). There were no differences between the LMWH's except for cumulative flow at high doses.

CONCLUSIONS

This study revealed no relevant differences between nadroparin and enoxaparin for the primary endpoints of our model. Clinical use of each drug remains a personal preference.