Study of Alfimeprase's Ability to Dissolve Blood Clots in the Leg and Help Prevent the Need for Surgery

Inclusion Criteria: Age 18 or older Arteriographically confirmed acute PAO of the lower extremity with onset of symptoms within 14 days prior to randomization Acute index limb ischemia classified as SVS/ISCVS Class I or IIa caused by occlusion of a native artery and/or bypass graft (vein or prosthetic). Only Class I subjects with abrupt onset of ischemic rest pain or abrupt onset/progression of lifestyle-limiting claudication are eligible Acute PAO with a need for urgent surgical intervention to restore arterial blood flow in the event of unsuccessful thrombolytic therapy Available for follow-up assessments Exclusion Criteria: Contraindication to systemic anticoagulation History of endovascular procedure or open vascular surgery on the index limb within the past 30 days History of significant acute or chronic kidney disease that would preclude contrast angiography Known allergy to contrast agents History of heparin induced thrombocytopenia Participation in any study of an investigational device, medication, biologic, or other agent within 30 days prior to randomization Any thrombolytic therapy within 5 days prior to randomization Past participation in any alfimeprase trial Pregnant, lactating, or actively menstruating women or women of childbearing potential who are not using adequate contraceptive precautions Investigator inability to advance guidewire through index occlusion Any other subject feature that in the opinion of the investigator should preclude study participation