Time to Target Anti-Xa Level in Obese Vs Nonobese Patients Using an Adjusted Body Weight Heparin Infusion Protocol for the Treatment of Venous Thromboembolism

Background: Unfractionated heparin (UFH) is a first-line option for the acute treatment of venous thromboembolism (VTE). Weight-based dosing protocols have demonstrated a decreased time to therapeutic anticoagulation, however, there are limited data on their utilization in obese patients, including the type of weight used. Objective: The purpose of this study was to determine equivalency in time to reach target antifactor-Xa (anti-Xa) for obese and nonobese patients using the same adjusted body weight (AdjBW)-based UFH infusion protocol. Methods: This was a single-center retrospective study of patients aged 18 years or older receiving an infusion of UFH for the treatment of VTE. The primary outcome was the median time to first target anti-Xa. Secondary outcomes included the percentage of first anti-Xa levels at 6 hours that were within, below, or above the target range and the median time to the second consecutive anti-Xa level within the target range. The safety outcome of evidence of major bleed was also evaluated. Results: Of the 166 patients assessed (75 obese and 91 nonobese), there was no observed difference in median time to first target anti-Xa in obese vs nonobese patients when using an AdjBW UFH protocol (12.45 vs 13.03 hours, P = 0.49). The percentage of patients achieving a target anti-Xa at first evaluation did not differ between obese and nonobese groups (32.0% vs 34.07%, P = 0.78). A total of 14 patients across groups experienced evidence of major bleed, with no observed difference between obese and nonobese groups (8.00% vs 8.89%, P = 0.84). Conclusions and Relevance: There was no observed difference in median time to first target anti-Xa in obese vs nonobese patients when using an AdjBW heparin infusion protocol, with no observed difference in evidence of major bleed. Our findings support the use of AdjBW in weight-based UFH dosing.