Inadequate enoxaparin dosing predicts 90-day venous thromboembolism risk among plastic surgery inpatients: an examination of enoxaparin pharmcodynamics.

Introduction: Evidence-based plastic surgery guidelines support the effectiveness of once daily enoxaparin prophylaxis. Despite prophylaxis, one in 25 highest risk patients has a VTE event. We examined the pharmacodynamics of standard enoxaparin doses in plastic surgery patients to examine whether patient-level factors predict enoxaparin metabolism, whether inadequate enoxaparin dose predicts downstream VTE events, and whether a pharmacist-driven dose adjustment protocol was effective. Methods: We recruited adult plastic surgery patients who received post-operative enoxaparin at 40mg daily. Steady state peak anti-Factor Xa (aFXa) levels, a marker of enoxaparin effectiveness and safety, were drawn. Patients with out of range aFXa levels had real-time dose adjustment based on a written protocol. Patients were followed for 90-day VTE events. Results: 94 patients were recruited, and 44% had in range peak aFXa levels in response to standard enoxaparin dosing. Patient-level factors including extent of surgical injury and gross weight were independent predictors of enoxaparin metabolism. Patients with low aFXa levels were significantly more likely to have 90-day VTE (10.2% vs. 0%, p=0.041). Real time dose adjustment allowed a significantly increased proportion of patients to have in range levels (67.1% vs. 44.3%, p=0.002). Conclusion: Based on pharmacodynamic data, the majority of plastic surgery patients receive inadequate enoxaparin prophylaxis using fixed dosing. Patient-level factors can predict how patients will metabolize enoxaparin, and patients who receive inadequate enoxaparin prophylaxis are significantly more likely to have downstream VTE events. Individualization of enoxaparin prophylaxis may minimize peri-operative VTE risk and further improve patient safety after plastic and reconstructive surgery procedures. (C)2016American Society of Plastic Surgeons

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