C. J. Pannucci1, K. I. Fleming1, L. Moulton2, A. Prazak3, T. K. Varghese2 1University Of Utah,Division Of Plastic Surgery,Salt Lake City, UTAH, USA 2University Of Utah,Division Of Cardiothoracic Surgery,Salt Lake City, UTAH, USA 3University Of Utah,Department Of Pharmacy,Salt Lake City, UTAH, USA
Introduction:
Thoracic surgery patients, particularly those with malignancy, are at elevated risk for perioperative venous thromboembolism (VTE). Enoxaparin prophylaxis prevents VTE amongst surgical patients. However, emerging literature demonstrates that enoxaparin is not a “one size fits all” intervention, and inadequate enoxaparin dosing has been associated with downstream VTE events in other surgical subspecialties. We examined the pharmacodynamics of enoxaparin 40mg per day in VATS patients with an emphasis on 1) dose adequacy, measured by peak and trough anti-Factor Xa (aFXa) levels and 2) the association between gross weight and peak aFXa level.
Methods:
We prospectively enrolled patients after VATS procedures into this ongoing clinical trial (NCT02704052). All patients received enoxaparin prophylaxis at 40mg once per day, initiated at 12-18 hours after their surgical procedure. Steady-state peak and trough aFXa levels, which mark enoxaparin effectiveness and safety, were drawn. Goal peak and trough aFXa levels were 0.3-0.5 IU/mL and 0.1-0.2 IU/mL, respectively. Patients with out of range peak aFXa levels had real time enoxaparin dose adjustment based on a written protocol, followed by repeat aFXa levels. Stratified analyses examined variation in peak aFXa by patient’s gross weight.
Results:
To date, 21 patients who received enoxaparin 40mg once daily after VATS surgery have been enrolled. 28.6% of patients had initial in range peak aFXa levels. 19.0% of patients had any detectable aFXa activity at 12 hours. Real time enoxaparin dose adjustment was performed based on peak aFXa levels, and 100% of patients in whom repeat labs were drawn had in-range levels. Gross weight was associated with peak steady state aFXa level in patients who received fixed dose prophylaxis (Figure 1). Patients with gross weight over 150 pounds were significantly more likely to have inadequate aFXa levels when compared to patients ≤150 pounds (86.7% vs. 33.3%, p=0.031).
Conclusion:
Enoxaparin 40mg once daily provides adequate prophylaxis for a minority of patients (28.6%) after VATS surgery. 19% of patients had any detectable aFXa activity at 12 hours. Thus, for a medication administered daily, four out of five patients receive chemoprophylaxis for less than 12 hours per day. Patients with gross weight >150 pounds were significantly more likely to have inadequate aFXa levels in response to fixed dosing. These preliminary findings support an individualized and possibly weight based approach to post-VATS chemoprophylaxis. Further research from this ongoing study will 1) correlate aFXa levels with downstream VTE and bleeding events and 2) examine additional patient-level predictors of enoxaparin metabolism after VATS.
