New therapies for unstable angina and non-Q-wave myocardial infarction: recent clinical trials

Review of enoxaparin and its clinical applications in venous and arterial thromboembolism

Venous and arterial thromboembolic disorders are common medical conditions that are associated with considerable morbidity and mortality. Unfractionated heparin (UFH) and its derivatives, the low molecular weight heparins (LMWHs), are the anticoagulants of choice when a rapid anticoagulant effect is required. LMWHs have several advantages over UFH, including a longer plasma half-life and higher bioavailability; a predictable dose response, which enables once- or twice-daily dosing; and a more convenient route of administration (subcutaneous instead of intravenous), which enables patients to self-inject in an out-patient setting. Enoxaparin is a LMWH prepared by alkaline hydrolysis of the benzylin ester of UFH. The efficacy of enoxaparin in the management of venous and arterial thromboembolism has been shown in a wide range of patient groups using doses ranging from fixed doses of 20 - 60 mg o.d. and 0.75 - 1.5 mg/kg b.i.d. Other doses, such as 80 mg/day for pregnant women with combined thrombophilic defects, have also been studied. The use of subcutaneous enoxaparin as an effective and safe home treatment for patients with acute proximal deep vein thrombosis (DVT) has been demonstrated. The benefits of preventing venous thromboembolic events with enoxaparin include reducing the costs associated with investigating the symptoms of DVT, acute treatment and hospitalisation, and potentially the development of post-thrombotic syndrome, while improving quality of life and so making the treatment cost effective. In contrast to other LMWHs, enoxaparin has been shown to provide better outcomes than UFH in the treatment of unstable angina and non-ST-segment elevation myocardial infarction, without increasing major bleeding. Adverse events with enoxaparin are infrequent; the most common events are minor bleeding complications. It should be noted that different doses or indications are approved in each country.

Newer antithrombotic strategies in the initial management of non-ST-segment elevation acute coronary syndromes

OBJECTIVE

To review the place in therapy of currently available antithrombotic agents in the non-ST-segment elevation acute coronary syndromes, that is, unstable angina and non-Q-wave myocardial infarction (MI). Recommendations are made based on currently available data.

DATA SOURCE

English-language clinical studies, position statements, and review articles pertaining to the management of unstable angina and non-Q-wave MI with currently available products.

STUDY SELECTION

Selection of prospective clinical studies was limited to those focusing on the management of the non-ST-segment elevation acute coronary syndromes, unstable angina, and non-Q-wave MI.

DATA SYNTHESIS

It has yet to be determined which combination of agents (dalteparin, enoxaparin, lepirudin, clopidogrel, ticlopidine, abciximab, eptifibatide, tirofiban) and procedural strategies most significantly reduces mortality and serious events in these patients. The relevant pathophysiology, diagnostic criteria, and risk-stratifying procedures are reviewed in context with information from clinical studies regarding currently available agents for the management of non-ST-segment elevation acute coronary syndromes.

CONCLUSIONS

A large number of new therapeutic classes and agents are available for the treatment of unstable angina and non-Q-wave MI. Although the diagnoses of unstable angina or non-Q-wave MI identify risk, treatment decisions are often based on the presence or absence of ST-segment elevations. Limited prospective evidence delineates the proper utilization of resources to best manage these patients. Efforts should be aimed at identifying particular patients who will best benefit from recently available therapies.

Biochemical markers in myocardial injury

Biochemical markers are substances that are detected in body fluids or tissues that may signify a disease or other abnormality. Biochemical markers have been used to help in the diagnosis of acute myocardial infarction since the 1950s. The major problem with these markers is that they lack specificity for cardiac muscle as they are also elevated in many disease states and after minor muscle damage.

[Practice guidelines of the Spanish Society of Cardiology. Recommendations for the use of antithrombotic treatment in cardiology]

The indications for the use of antithrombotic therapy are evolving as new drugs become available or new indications or dosages are recommended for drugs already in use. This document reviews and updates the former one published in 1994. To that end, an exhaustive revision of the literature published in the last 15 years has been undertaken. Following the evidence based medicine dictates, and aiming to select all the relevant publications for each pathology, all studies were selected through MEDLINE, using the specified key words for each subject, and were filtered using the following steps: a) only randomized, controlled studies, meta-analysis, guidelines and review articles were chosen; b) then, the Best-Evidence and Cochrane Collaboration databases were consulted; c) finally, the evidence based medicine validation, relevance and applicability criteria were assessed for each publication. The use of antiaggregants and anticoagulants are given for the following conditions: a) prevention of deep vein thrombosis and pulmonary embolism; b) prevention of systemic emboli in patients with lone atrial fibrillation, atrial fibrillation associated or not with rheumatic heart disease, in patients with biological or mechanical cardiac valvular prostheses and in dilated cardiomyopathy; c) antithrombotic therapy in coronary heart disease and in coronary intervention; d) the interactions with oral anticoagulants and how to control these therapies are also discussed.

TIMI 11B. Enoxaparin versus unfractionated heparin for unstable angina or non-Q-wave myocardial infarction: a double-blind, placebo-controlled, parallel-group, multicenter trial. Rationale, study design, and methods. Thrombolysis in Myocardial Infarction (TIMI) 11B Trial Investigators

Continuous intravenous (i.v.) heparin administered in the acute period after unstable coronary artery disease reduces the likelihood and severity of subsequent ischemic events. However, reactivation of the thrombotic process may occur when heparin therapy is withdrawn. Low-molecular-weight heparin provides more reliable anticoagulation and less need for patient monitoring and dosage adjustment than standard unfractionated heparin (UFH) and therefore is well suited for long-term anticoagulation on an outpatient basis. TIMI 11B is a randomized, double-blind, placebo-controlled clinical trial designed to compare the strategy of combined short-term and long-term administration of the low-molecular-weight heparin enoxaparin for unstable angina/non-Q-wave myocardial infarction versus the standard strategy of UFH administration only during the acute phase. Patients are randomized to receive either enoxaparin (30 mg i.v. bolus followed by subcutaneous (s.c.) injections of 1.0 mg/kg every 12 hours) or UFH (70 U/kg bolus followed by an infusion of 15 U/kg per hour, titrated to an activated partial thromboplastin time of 1.5 to 2.5 times control). Infusion of i.v. UFH or placebo continues for a minimum of 72 hours. S.c. weight-adjusted enoxaparin or placebo continues until hospital discharge or day 8, whichever comes first, at which time the long-term phase of the study begins. Patients randomized to receive enoxaparin in the acute phase receive fixed-dose s.c. enoxaparin (60 mg every 12 hours for patients > or =65 kg, 40 mg every 12 hours for patients <65 kg). Patients randomized to receive UFH in the acute phase receive s.c. placebo injections during the chronic phase. The primary efficacy endpoint is the sum, through day 43, of the occurrence of death, nonfatal myocardial infarction not present at enrollment, or severe recurrent ischemia requiring urgent revascularization. The primary safety endpoint is the occurrence of either major bleeding or other serious adverse events.