OASIS Pilot

Organization to Assess Strategies for Ischemic Syndromes pilot study (1998)

Condition

Treatment of unstable angina or myocardial infarction without ST elevation (NSTEMI) after 3 days of intravenous antithrombotic therapy

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Objective

To investigate the efficacy and safety of low-intensity warfarin and then, in a second trial phase, the effects of moderate-intensity warfarin in patients with unstable angina or NSTEMI

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Trial design

Randomized, controlled open-label study

Active treatment:

  • Phase 1: warfarin (target INR 1.5) and ASA (325 mg once daily in 87% of patients) (n=155)
  • Phase 2: warfarin (target INR 2.0 – 2.5) and ASA (325 mg once daily in 85% of patients) (n=98)

Control treatment:

  • Phase 1: standard therapy (ASA 325 mg once daily in 87% of patients) (n=154)
  • Phase 2: standard therapy (ASA 325 mg once daily in 85% of patients) (n=99)

 

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Endpoints

Primary efficacy endpoint: combined endpoint of cardiovascular death, new myocardial infarction or refractory angina
Secondary efficacy endpoints: combined endpoint of CV death, new myocardial infarction, refractory angina or severe angina; rehospitalization with unstable angina
Safety endpoints: stroke, major and minor bleeding

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Trial participants

309 (phase 1) and 197 (phase 2) patients with unstable angina or NSTEMI after 3 days of intravenous antithrombotic therapy

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Results

Primary outcome: In phase 1 of the study, the primary outcome occurred in 10 of 155 patients (6.5%) receiving warfarin and ASA and in 6 of 154 (3.9%) receiving ASA alone (relative risk +1.66 %). In phase 2, 5 of 98 patients assigned to warfarin and ASA (5.1%) and 12 of 99 patients assigned to ASA (12.1%) experienced a primary event (relative risk reduction 58%)
Safety outcome: In phase 1, the risk of major bleeding was 2.6% (n=4) in patients given warfarin + ASA compared to 0% in ASA patients. In phase 2, 2 patients assigned to warfarin + ASA (2.0%) experienced a major bleeding complication compared to 1 patient (1.0%) assigned to ASA

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Summary

Efficacy: In phase 1 with the low-intensity therapy there were no benefits of warfarin compared to standard therapy. In phase 2 with higher dosage of warfarin the combination of warfarin and ASA strongly reduced the rate of acute ischemic syndromes when compared to ASA alone
Safety: In both phases of this study there were higher rates of bleeding complications in patients receiving warfarin + ASA when compared to ASA alone

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Reference

Anand SS, Yusuf S, Pogue J, Weitz JI, Flather M. Long-term oral anticoagulant therapy in patients with unstable angina or suspected non-Q-wave myocardial infarction: Organization to Assess Strategies for Ischemic Syndromes (OASIS) pilot study results. Circulation 1998;98:1064-1070

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Corresponding author

Sonia Anand, MD, McMaster Clinic-2nd Floor, 237 Barton Street East, Hamilton, Ontario, L8L 2X2, Canada

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