Presentation Authors: Lauren E Corona*, Udit Singhal, Khaled Hafez, Lindsey Herrel, Samuel Kaffenberger, Jeffrey Montgomery, Todd M Morgan, Alon Z Weizer, Yongmei Qin, Sapan N Ambani, Ann Arbor, MI
Introduction: Empirically dosed enoxaparin is routinely given in the immediate postoperative period for venous thromboembolism (VTE) prophylaxis after radical cystectomy (RC). Although the simplicity and lack of titration of enoxaparin dosing is seen as advantageous, patient specific factors may alter its pharmacokinetics, and it is unclear whether this leads to levels sufficient to provide an anti-thrombotic effect. We sought to evaluate the variability of anti-Xa levels in a weight-based and renally dosed cohort of RC patients receiving perioperative enoxaparin prophylaxis.
Methods: Beginning in January 2018, patients undergoing radical cystectomy at a single institution were placed on a postoperative pathway that included enoxaparin for VTE prophylaxis. The standard dose was 40 mg daily, and 30 mg daily was used for creatinine clearance of 10-29 mL/min, while 40 mg twice daily was used for body mass index (BMI) >40 kg/m2. An anti-Xa level was drawn 2-4 hours after the third dose. Target range for prophylaxis was 0.2-0.5 IU/mL. The primary outcome was anti-Xa level. Demographics, operative time, hospital course, and 30-day post-operative VTE were compared according to anti-Xa level.
Results: Between January and September 2018, 145 patients underwent RC. Fifty-four patients were excluded from our analysis-29 of whom were placed on heparin prophylaxis and 25 with a missed or faulty anti-Xa level draw. There was 1 VTE event that occurred in those excluded (patient on heparin). 91 patients remained on pathway and were included in our analysis. 21 (23.1%) were below target range for VTE prophylaxis. No patients were supraprophylactic. 73% were discharged on 30 days of enoxaparin for continued VTE prophylaxis. A single VTE event (1.1%) occurred in an individual that was subprophylactic. The subprophylactic group had a significantly higher BMI (33 v 28 kg/m2, p=0.0001) than those within target range. On univariate analysis, higher BMI led to an increased risk of subprophylactic anti-Xa level (OR 1.2, 95% CI 1.1-1.4, p=0.0001). There were no differences in anti-Xa levels based on age, race, VTE history, operative time, or creatinine clearance.
Conclusions: Higher BMI was associated with subprophylactic enoxaparin dosing after RC in a weight-based and renally dosed cohort of patients. Nearly one quarter of our cohort had below target anti-Xa levels despite standard dosing. This suggests that dosing could be further individualized, providing an even wider window of efficacy. Further studies are needed to determine the implications of dose-adjusted prophylaxis on VTE prevention.