Comparison of postpartum anti-xa levels following enoxaparin administration to prevent venous thromboembolism using two protocols

During the puerperium enoxaparin is given to high risk women to prevent venous thromboembolism, which is the leading cause for maternal mortality. Enoxaparin activity is measured by plasma anti-Xa levels. The prophylactic range of anti-Xa is 0.2-0.6 units/ml. Values above and below this range represent overdose and suboptimal anticoagulation activity, respectively. Enoxaparin may be administered according to weight categories or as 1mg/kg/day body weight. We aimed to compare the efficacy and adverse effects of the two enoxaparin dosing protocols. A randomized open label controlled trial was conducted. Women after delivery, who were intended to receive enoxaparin, were randomized to receive either enoxaparin treatment according to weight categories (≤ 90kg - 40mg; 91-130kg - 60mg; 131-170kg - 80mg; >170kg - 100mg) or as 1mg/kg (up to 100mg) .Plasma anti-Xa levels were obtained 4 hours after the second enoxaparin injection (day 2 of enoxaparin treatment). If the woman was still hospitalized, anti-Xa levels were also obtained at day 4. Assuming that 90% and 70% of women will have anti-Xa levels within the prophylactic range (0.2-0.6 units/ml) in the 1 mg/kg and weight categories groups, respectively, 124 women were required (2-sided alpha, 80% power). The primary outcome was the proportion of women with anti-Xa levels within the prophylactic range (0.2-0.6 units/ml) at day 2. 64 and 60 women received enoxaparin according to weight categories and 1mg/kg, respectively; mean anti-Xa levels at day 2 were 0.19±0.06 and 0.34±0.09 (P< .0001) and 27 (42%) and 55 (92%) women reached the prophylactic range of anti-Xa at day 2, respectively (P< .0001). In the 25 women that had anti-Xa measurements at day 4, there was no difference in anti-Xa levels when compared to day 2. There were no adverse events or anti-Xa > 0.6 units/ml. Postpartum enoxaparin administration at 1mg/kg was superior to weight categories in reaching anti-Xa prophylactic levels without leading to overdose.View Large Image Figure ViewerDownload Hi-res image Download (PPT)