Weight-Based Enoxaparin Dosing and Real-Time Dose Adjustment in Orthopaedic Trauma

The rates of Venous thromboembolism (VTE) after orthopedic surgery are as high as 40-60% without prophylactic measures. Enoxaparin, a low-molecular-weight heparin, produces an anticoagulant effect by binding antithrombin, thereby accelerating antithrombin's inactivation of coagulation factor Xa (FXa), thus decreasing the likelihood of clot formation. Despite standard dosing enoxaparin prophylaxis, VTE rates in post-operative orthopedic trauma patients remain as high as 12.2%.The investigators will examine enoxaparin pharmacokinetics and test whether a clinical protocol for real-time enoxaparin dose adjustment can favorably alter the proportion of patients with in-range anti-Factor Xa (aFXa) levels. Outcomes will include peak and trough steady-state aFXa levels in response to standard and escalated doses of enoxaparin and the incidence of venous thromboembolism and bleeding events post-surgery. In the trauma and orthopaedic populations, patients with low initial aFXa levels are significantly more likely to develop deep venous thrombosis. Thus, this study has important implications for appropriate enoxaparin dose magnitude and frequency, and may ultimately help to decrease the substantial morbidity and mortality associated with post-operative VTE.

Eligible patients will have steady state peak and trough anti-Xa levels drawn after the third enoxaparin dose. For patients in-range (levels 0.2-0.4 IU/mL), no intervention will be undertaken. For patients out of range, enoxaparin dose will be adjusted according to an established dose adjustment algorithm. Repeat levels will be checked after the third administration of the new dose.

Enrolled patients will receive real-time monitoring of peak and trough steady state anti-Xa levels. Out-of-range patients will receive real time dose adjustment of Enoxaparin using a clinical protocol developed with our inpatient pharmacists.

Any symptomatic venous thromboembolism events, including deep venous thrombosis or pulmonary embolus occurring within 90 days of surgery

Inclusion Criteria: Receiving orthopedic trauma surgery Able to have enoxaparin initiated within 36 hours after procedure Exclusion Criteria: Intracranial bleeding/stroke bleeding disorder heparin-induced thrombocytopenia creatinine clearance < 30 mL/minute epidural catheter serum creatinine > 1.6 mg/dL