Enoxaparin, a low-molecular-weight heparin suppresses prothrombin activation more effectively than unfractionated heparin in patients treated for venous thromboembolism.

Although unfractionated heparin (UFH) is standard therapy for venous thromboembolism, there is a clinical failure rate of up to 10%. Newer treatment strategies include low-molecular-weight heparins (LMWH). As part of an international study comparing the efficacy and safety of enoxaparin, a LMWH versus UFH in patients with venous thromboembolism, we studied the effects of enoxaparin and UFH on the plasma concentrations of two activation peptides, fragment 1 + 2 (F1 + 2), and thrombin-antithrombin III (TAT) complexes. We hypothesized that enoxaparin would be more effective in suppressing activation of coagulation. Intravenous heparin was given by bolus injection followed by infusion. There were 2 enoxaparin treatment groups (1 mg/kg s.c., bid and 1.5 mg/kg s.c. daily). Plasma samples were obtained from 11 patients in the enoxaparin group and 6 patients in the heparin group prior to and at 6 hour intervals after initiating therapy. Clinical characteristics of the enoxaparin and UFH patient groups were similar. TAT concentrations were not statistically different between groups at any treatment interval. However, plasma F1 + 2 concentrations differed significantly (p < 0.05); concentrations in the enoxaparin group were consistently lower over time than in the UFH group. These results suggest that this LMWH is more effective in suppressing ongoing thrombosis in vivo than UFH in patients with venous thrombosis.