Optimal Dosing of Prophylactic Enoxaparin after Surgical Procedures: Results of the Double-Blind, Randomized, Controlled FIxed or Variable Enoxaparin (FIVE) Trial

Abstract

P annucci et al. 1 conclude that prescribing enoxaparin 0.5 mg/kg twice daily is effective and safe for venous thromboembolism prevention. 1 The authors measure anti-factor Xa levels. These levels reflect enoxaparin activity, not the anticoagulation effect. 2 Weight-based dosing was found to be superior to fixed doses in avoiding overdoses (9.4 percent versus 17.8 percent, p = 0.046) when controlling for patient age and central lines. The effect of either variable on antifactor Xa levels is unexplained.The authors reference an earlier study 3 suggesting that patients with low anti-factor Xa levels are more likely (p = 0.041) to develop venous thromboembolism. Three of the five cases of venous thromboembolism in that underpowered study (n = 94) represented upper extremity thromboses in patients with central catheters. 3 Such thromboses have a different etiology (i.e., intimal trauma rather than venous stasis). Patients with low anti-factor Xa levels who developed venous thromboembolism also received extra doses of enoxaparin, which would theoretically remedy the low anti-factor Xa levels.Pannucci et al. 4 previously reported a 6.8 percent risk of clinically relevant bleeding in patients who received enoxaparin 40 mg twice daily.