Pharmacological and clinical profile of bivalirudin in the treatment of patients with acute coronary syndrome

Direct thrombin inhibitors in cardiovascular disease

Limitations of commonly used anticoagulants, unfractionated heparin, low-molecular-weight heparin, and oral vitamin K antagonists have prompted the development of alternative therapies. Direct thrombin inhibitors are a new class of anticoagulants that bind directly to thrombin and inhibit its interaction with substrates. In this Review, we critically examine the evidence from randomized controlled trials for the efficacy and safety of the parenteral direct thrombin inhibitors bivalirudin and argatroban, and the novel oral direct thrombin inhibitor dabigatran etexilate, in cardiovascular and thrombotic disease.

Cost effectiveness of anticoagulation in acute coronary syndromes

BACKGROUND

The benefit of unfractionated heparin (UFH) added to aspirin in patients with acute coronary syndromes (ACS) was described more than 20 years ago. Ever since, a wide variety of anticoagulant drugs have become available for clinical use, including low-molecular-weight heparins (LMWH), direct thrombin inhibitors and selective factor Xa inhibitors.

OBJECTIVE

The aim of this study was to critically review the available evidence on the cost and incremental cost effectiveness of anticoagulants in patients with ACS.

METHODS

Studies were identified using specialist databases (UK NHS Economic Evaluation Database [NHS EED] and Cost-Effectiveness Analysis [CEA] Registry), PubMed and the reference lists of recovered articles. Only studies based on randomized controlled trials were considered for inclusion. Finally, 22 studies were included in the review.

RESULTS

Enoxaparin is the only LMWH that has been shown to reduce the risk of death or myocardial infarction in patients with non-ST-elevation ACS (NSTE-ACS). In economic studies based on the ESSENCE trial conducted in the late 1990s, enoxaparin was consistently associated with a lower risk of coronary events, a reduction in the number of revascularization procedures and a lower cost per patient than UFH. However, these results refer to patients managed conservatively, with little use of thienopyridines and glycoprotein IIb/IIIa inhibitors, and the results are difficult to extrapolate to moderate-to-high-risk patients managed with the present day early invasive strategy. Available studies of LMWH in ACS with persistent elevation of ST-segment (STE-ACS) are limited to patients treated with thrombolysis. In this scenario, enoxaparin was shown to be a dominant alternative compared with UFH in a study based on the ASSENT-3 study and was considered an economically attractive alternative in three studies based on the ExTRACT-TIMI 25 study. However, these results should be interpreted cautiously due to the heterogeneity of the supportive randomized trials and the possible underestimation of bleeding costs. The effectiveness and safety of bivalirudin, a direct thrombin inhibitor, were evaluated in the ACUITY study (NSTE-ACS patients managed invasively) and the HORIZONS-AMI study (STE acute myocardial infarction patients planned for primary percutaneous coronary intervention). Bivalirudin monotherapy was not inferior to heparin plus a glycoprotein IIb/IIIa inhibitor and reduced the risk of major bleeding. The economic evaluations based on these studies suggest that bivalirudin is an attractive alternative to heparin plus a glycoprotein-IIb/IIIa inhibitor. In the OASIS-5 trial, compared with enoxaparin, fondaparinux reduced the mortality in patients with NSTE-ACS, probably because of a reduced risk of bleeding. In three economic evaluations of fondaparinux versus enoxaparin based on this trial, fondaparinux was the dominant strategy in two of them, and still economically attractive in a third. Taken as a whole, the usefulness of economic studies of anticoagulants in patients with ACS is undermined by the quality of the evidence about their effectiveness and safety; the narrow spectrum of the analysed scenarios; the lack of economic evaluations based on systematic reviews; the limitations of sensitivity analyses reported by the available economic evaluations; and their substantial risk of commercial bias.

CONCLUSIONS

The available studies suggest that enoxaparin is an economically attractive alternative compared with UFH in patients with NSTE-ACS treated conservatively and STE-ACS patients treated with thrombolysis. Bivalirudin in patients with ACS treated invasively is cost effective compared with heparin plus a glycoprotein IIb/IIIa inhibitor. In patients with NSTE-ACS, fondaparinux is cost effective compared with enoxaparin. The usefulness of these results for decision making in contemporary clinical practice is limited due to problems of internal and external validity.

Parenteral anticoagulants: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

This article describes the pharmacology of approved parenteral anticoagulants. These include the indirect anticoagulants, unfractionated heparin (UFH), low-molecular-weight heparins (LMWHs), fondaparinux, and danaparoid, as well as the direct thrombin inhibitors hirudin, bivalirudin, and argatroban. UFH is a heterogeneous mixture of glycosaminoglycans that bind to antithrombin via a unique pentasaccharide sequence and catalyze the inactivation of thrombin, factor Xa, and other clotting enzymes. Heparin also binds to cells and plasma proteins other than antithrombin causing unpredictable pharmacokinetic and pharmacodynamic properties and triggering nonhemorrhagic side effects, such as heparin-induced thrombocytopenia (HIT) and osteoporosis. LMWHs have greater inhibitory activity against factor Xa than thrombin and exhibit less binding to cells and plasma proteins than heparin. Consequently, LMWH preparations have more predictable pharmacokinetic and pharmacodynamic properties, have a longer half-life than heparin, and are associated with a lower risk of nonhemorrhagic side effects. LMWHs can be administered once daily or bid by subcutaneous injection, without coagulation monitoring. Based on their greater convenience, LMWHs have replaced UFH for many clinical indications. Fondaparinux, a synthetic pentasaccharide, catalyzes the inhibition of factor Xa, but not thrombin, in an antithrombin-dependent fashion. Fondaparinux binds only to antithrombin. Therefore, fondaparinux-associated HIT or osteoporosis is unlikely to occur. Fondaparinux exhibits complete bioavailability when administered subcutaneously, has a longer half-life than LMWHs, and is given once daily by subcutaneous injection in fixed doses, without coagulation monitoring. Three additional parenteral direct thrombin inhibitors and danaparoid are approved as alternatives to heparin in patients with HIT.