Superiority of enoxaparin versus unfractionated heparin for unstable angina/non-Q-wave myocardial infarction regardless of activated partial thromboplastin time

Background Whether the clinical superiority of enoxaparin versus unfraction ated heparin (UFH) depends on a more stable antithrombotic effect or the pr oportion of patients not reaching the therapeutic level with UFH has not be en addressed. Methods All patients participating in the Thrombolysis In Myocardial Infarc tion 11B trial who received UFH and had sufficient activated partial thromb oplastin time (aPTT) data (n = 1893) were compared with patients who receiv ed enoxaparin (n = 1938). Patients receiving UFH were divided into 3 catego ries depending on mean aPTT values throughout 48 hours: subtherapeutic, for those in whom the average aPTT fell below 55 seconds; therapeutic, between 55 and 85 seconds; and supratherapeutic, longer than 85 seconds. Events an d bleeding rates were determined at 48 hours. Results A small portion of patients (6.7%) had a subtherapeutic average aPT T value (n = 127). Forty-seven percent of patients (n = 891) fell within th e therapeutic range, and 46% were in the supratherapeutic level (n = 875). Event rates were 7.0% in the UFH group versus 5.4% with enoxaparin (P= .039 ). Events rates were higher in every aPTT strata compared with enoxaparin a nd statistically significant in the supratherapeutic group (odds ratio 0.65 ; 95% confidence interval, 0.47-0.89). Major bleeding rates were 0%, 0.6%, and 0.9% for the subtherapeutic, target, and supratherapeutic strata, respe ctively, and 0.8% with enoxaparin. Minor hemorrhages occurred in 5.1% of pa tients receiving enoxaparin versus 3.9%, 2%, and 2.3%, respectively, for th e UFH subgroups (P < .001 for all UFH groups vs enoxaparin). Conclusions Enoxaparin showed a better clinical profile compared with every level of anticoagulation with UFH. Potential mechanisms for enoxaparin sup eriority are stable antithrombotic activity, lack of rebound thrombosis, an d intrinsic superiority.