- Need for antiplatelet agent (eg, aspirin, ticlopidine, clopidogrel, dipyridamole), unfractionated or low molecular weight heparin, direct thrombin inhibitor, Factor Xa inhibitor, oral anticoagulant, or NSAID (excluding COX-2 inhibitor) before the post study-agent head CT scan. Treatment with aspirin prior to randomization is not an exclusion criterion.