Effects of Long-Term, Moderate-Intensity Oral Anticoagulation in Addition to Aspirin in Unstable Angina - OASIS-2


In this trial, investigators sought to evaluate whether oral anticoagulant (AC) therapy given for five months was superior to standard (control) therapy in patients with unstable angina receiving aspirin


Is oral AC therapy given for five months superior to standard therapy in patients with unstable angina receiving aspirin?

Study Design

Study Design:

Patients Enrolled: 10,141

Drug/Procedures Used:

The Organization to Assess Strategies for Ischemic Syndromes-2 (OASIS-2) trial compared a three-day regimen of heparin versus hirudin in patients with unstable angina or non-ST-elevation myocardial infarction (MI). Of the 10,141 patients enrolled in this study, 3,712 already on aspirin were randomized 12 to 48 hours later to receive oral AC therapy (n=1,848) or standard therapy (n=1,864).

Principal Findings:

The primary endpoint (cardiovascular death, MI, or stroke) occurred in 140 patients (7.6%) receiving oral ACs compared with 155 patients (8.3%) on standard therapy (relative risk [RR] 0.90, 95% confidence interval [CI] 0.72-1.14; p=0.40). Secondary outcome rates (cardiovascular death, MI, or stroke) were 16.7% (n=308) versus 17.5% (n=327) (RR 0.95, 95% CI 0.81-1.11; p=0.53).

There were significant reductions in the risks of both the primary and secondary outcomes with oral AC in the "good-complier" countries (those with oral AC used ≥70% at 35 days), with little difference in the "poor-complier" countries for both endpoints. Overall, there was an excess of major bleeding (2.7% vs. 1.3%; p=0.004), which was larger in the good-complier countries (RR 2.71) compared with the poor-complier countries (RR 1.58). There were reductions in cardiac catheterization (RR 0.80; p=0.004) and coronary revascularization procedures (RR 0.82; p=0.06) in the good-complier countries, but not in the poor-complier countries.

Oral anticoagulation in addition to aspirin, resulted in a small, nonsignificant reduction in the risk of the primary and secondary endpoints that was more pronounced in the "good-complier" countries.


This study demonstrated the modest potential benefit of adding anticoagulation to aspirin to improve outcomes in patients with unstable angina/non-ST elevation MI (albeit with increased risk of bleeding). The study highlights another important well-known issue with such therapy: patients' noncompliance and physicians' reluctance to expose their patients to long-term monitoring and risks of oral anticoagulation. Further studies are needed to help claify the risk-benefit ratio of combined antiplatelet and AC therapy.


Effects of long-term, moderate-intensity oral anticoagulation in addition to aspirin in unstable angina. The Organization to Assess Strategies for Ischemic Syndromes (OASIS) Investigators. J Am Coll Cardiol 2001;37:475-84.

Clinical Topics: Anticoagulation Management

Keywords: Risk, Myocardial Infarction, Stroke, Platelet Aggregation Inhibitors, Research Personnel, Cardiac Catheterization, Heparin, Confidence Intervals, Hirudins

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