Implications of the Organization to Assess Strategies for Ischemic Syndromes–2 (OASIS–2) study and the results in the context of other trials

Although unfractionated heparin is widely used for thrombin inhibition in the management of unstable coronary artery disease, clinical and experimental evidence suggests that it is suboptimal. Recent pharmaceutical strategies to improve upon unfractionated heparin’s efficacy profile have centered on the development of 2 major classifications of thrombin inhibition medications: the naturally occurring leech protein hirudin (and synthetic analogs) and low-molecular-weight (LMW) heparins. In the Organisation to Assess Strategies for Ischaemic Syndromes-2 (OASIS-2) trial, hirudin was demonstrably more effective than heparin in diminishing rates of death, myocardial infarction (MI), and angina at both 72 hours and 7 days after unstable coronary artery disease index events, with risk ratios on the order of 0.8. Similarly, in the Efficacy and Safety of Subcutaneous Enoxaparin in Non–Q-Wave Coronary Events (ESSENCE) study, the LMW heparin enoxaparin emerged superior to unfractionated heparin in attenuating rates of unstable coronary artery disease at 14 days, 30 days, and 1 year. On the other hand, findings involving other LMW heparins (dalteparin sodium, Fragmin, and fraxaparin) are equivocal. Although the Fragmin During Instability in Coronary Artery Disease (FRISC) study demonstrated statistically significant superiority of this LMW heparin over aspirin/placebo in driving down death/MI/revascularization rates, the Fragmin in Unstable Coronary Artery Disease (FRIC) trial showed no such superiority, but had wide confidence intervals. Similarly, the Fraxaparin Versus Unfractionated Heparin in Acute Coronary Syndromes (FRAXIS) trial with fraxaparin failed to show superiority over unfractionated heparin. The favorable efficacy findings associated with hirudin and enoxaparin regimens, compared with unfractionated heparin, accrued without significant increases in the incidences of life-threatening bleeding events (e.g., hemorrhagic stroke), but did include more frequent lesser bleeding events. In summary, both hirudin and enoxaparin have demonstrated clinically important improvements in outcome compared with standard treatments in unstable coronary artery disease.