Performance of PCI with enoxaparin may be rea- sonable in patients either treated with upstream subcutaneous enoxaparin for UA/NSTEMI or who have not received prior antithrombin therapy and are administered IV enoxaparin at the time of PCI.646 650 (Level of Evidence: B) Class III: HARM 1. UFH should not be given to patients already receiving therapeutic subcutaneous enoxa- parin.649,665 (Level of Evidence: B) Trials of enoxaparin relevant to PCI include both studies in which patients with UA/NSTEMI were started on upstream subcutaneous enoxaparin therapy that was continued up to the time of PCI and trials in which patients who had received no prior antithrombin therapy were treated with IV enoxaparin at the time of PCI.646 650,661 663,666 In the SYNERGY (Superior Yield of the New strategy of Enoxa- parin, Revascularization and Glycoprotein IIb/IIIa Inhibi- tors) trial, there was an increased incidence of bleeding in those treated with upstream enoxaparin, later attributed at least in part to the fact that some patients being treated with enoxaparin were also administered UFH at the time of PCI (so-called stacking ).649,665 Almost all patients un- dergoing elective PCI who are administered enoxaparin (0.5 mg/kg IV) will have a peak anti-Xa level 0.5 IU/mL.647 Most clinical studies have used a regimen of 0.5 to 0.75 mg IV.667 Several studies have used this regimen in elective patients and those with STEMI.646 Patients who have received multiple doses of subcutaneously adminis- tered enoxaparin who undergo PCI within 8 hours of the last subcutaneous dose generally have adequate degrees of anticoagulation to undergo PCI, but the degree of antico- agulation may diminish in the 8- to 12-hour period after the last subcutaneous dose. 