Bozovich, G. E., Gurfinkel, E. P., Antman, E. M., McCabe, C. H., Mautner, B. Superiority of enoxaparin versus unfractionated heparin for unstable angina/non-Q-wave myocardial infarction regardless of activated partial thromboplastin time Am Heart J. 2000;140(4):637-42.

BACKGROUND: Whether the clinical superiority of enoxaparin versus unfractionated heparin (UFH) depends on a more stable antithrombotic effect or the proportion of patients not reaching the therapeutic level with UFH has not been addressed.

METHODS: All patients participating in the Thrombolysis In Myocardial Infarction 11B trial who received UFH and had sufficient activated partial thromboplastin time (aPTT) data (n = 1893) were compared with patients who received enoxaparin (n = 1938). Patients receiving UFH were divided into 3 categories 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 and bleeding rates were determined at 48 hours.

RESULTS: A small portion of patients (6. 7%) had a subtherapeutic average aPTT value (n = 127). Forty-seven percent of patients (n = 891) fell within the 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 and 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, respectively, and 0.8% with enoxaparin. Minor hemorrhages occurred in 5.1% of patients receiving enoxaparin versus 3.9%, 2%, and 2.3%, respectively, for the 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 superiority are stable antithrombotic activity, lack of rebound thrombosis, and intrinsic superiority.

Trial: TIMI 11B