Weight-Based Dosing for Once-Daily Enoxaparin Cannot Provide Adequate Anticoagulation for Venous Thromboembolism Prophylaxis

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Background:Surgeons commonly provide enoxaparin prophylaxis to high-risk patients to decrease venous thromboembolism risk. The authors’ prior work demonstrated that most patients receive inadequate venous thromboembolism prophylaxis, based on anti–factor Xa level, when enoxaparin 40 mg/day is provided and that peak anti–factor Xa level correlates with weight. This study models a weight-based strategy for daily enoxaparin prophylaxis and its impact on anti–factor Xa levels.Methods:The authors enrolled plastic surgery patients who received enoxaparin 40 mg/day and had anti–factor Xa levels drawn. The enoxaparin dose of 40 mg was converted to a milligram-per-kilogram dose for each patient. Stratified analysis examined the milligram-per-kilogram dose that produced low, in-range, and high anti–factor Xa levels to identify the appropriate milligram-per-kilogram dose to optimize venous thromboembolism prevention and bleeding events.Results:Among 94 patients, weight-based dosing ranged from 0.28 to 0.94 mg/kg once daily. For peak and trough anti–factor Xa levels, there was nearly complete overlap for milligram-per-kilogram dosing that produced low versus in-range anti–factor Xa levels. For peak anti–factor Xa, there was nearly complete overlap for milligram-per-kilogram dosing that produced in-range versus high anti–factor Xa levels. Mean milligram-per-kilogram dose was not significantly different between patients who did or did not have postoperative venous thromboembolism (0.41 mg/kg versus 0.52 mg/kg; p = 0.085) or clinically relevant bleeding (0.48 mg/kg versus 0.51 mg/kg; p = 0.73).Conclusions:Alterations in enoxaparin dose magnitude based on patient weight cannot allow a high proportion of patients to achieve appropriate anti–factor Xa levels when once-daily enoxaparin prophylaxis is provided. Future research should examine the impact of increased enoxaparin dose frequency on anti–factor Xa levels, venous thromboembolism events, and bleeding.CLINICAL QUESTION/LEVEL OF EVIDENCE:Therapeutic, IV.

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