(192) Evaluation of Unfractionated Heparin Dosing in Non-Obese Versus Obese Patients for VTE

Introduction: The pharmacokinetic profile of unfractionated heparin (UFH) may result in supratherapeutic anti-Xa levels using actual weight-based protocols for the treatment of venous thromboembolism (VTE) in obese patients. Previous literature has been limited by choice of monitoring assay and inconsistent dosing strategies. The goal of this study was to evaluate safety and efficacy outcomes of an anti-Xa based UFH VTE protocol in obese vs. non-obese patients.

Methods: This was a single center, retrospective study of adult patients with an acute VTE treated with our institution specific UFH VTE protocol. Patients were screened from the preceding 3 years for inclusion into the obese (BMI ≥30 kg/m2) or non-obese (BMI < 30 kg/m2) groups. The primary outcome was the weight-based rate of UFH required to attain a therapeutic anti-Xa level. Other outcomes included weight-based rate to attain steady state, proportion of anti-Xa levels being within sub-, supra-, and therapeutic ranges, and rates of major and non-major bleeding.

Results: The primary outcome of weight-based rate at first therapeutic anti-Xa level was significantly lower in the obese group, and this was consistent for attainment of steady state, as well (14 vs. 16 units/kg/hour, p= < 0.001). Patients in the obese group had significantly more supratherapeutic anti-Xa levels within 24 hours (50% vs. 33%, p< 0.0001) and for the total duration of UFH therapy (40% vs. 25%, p< 0.0001). No significant difference in adjusted bleeding rate was found.

Conclusions: Obese patients required a lower weight-based rate of UFH to attain therapeutic anti-Xa levels for the treatment of VTE. Future studies should focus on dosing strategies that improve attainment of therapeutic anti-Xa levels in obese patients.