Evaluating Frequency of Anti-Xa Monitoring in Treatment of Pediatric Venous Thromboembolism

BACKGROUND/INTRODUCTION: With the rising incidence of pediatric venous thromboembolism (VTE), it is imperative that anticoagulation treatment protocols are standardized. While unfractionated heparin and warfarin were considered the standards of care, enoxaparin has now become the drug of choice in many pediatric institutions, given improved efficacy, fewer bleeding complications, and a more favorable pharmacokinetic profile. The increased bioavailability, predictable dose response, and less frequent drug monitoring have made enoxaparin popular in the adult population. In pediatrics, there are insufficient guidelines regarding frequency of enoxaparin monitoring. At Texas Children's Hospital (TCH), we titrate the enoxaparin dose during initial hospitalization to a therapeutic Anti-Xa level of 0.5 - 1.0 units/mL. Patients are instructed to return for outpatient follow-up levels within 9 days of discharge, and monthly thereafter. It is unclear whether this frequency of monitoring is optimal.

OBJECTIVES: In an effort to reduce overall patient morbidity and healthcare costs, we evaluated current Anti-Xa level monitoring practices in children with VTEs at TCH to develop recommendations for standardizing Anti-Xa level monitoring.

METHODS: Using the TCH DVT Registry, we retrospectively identified 107 subjects diagnosed with uncomplicated VTE and treated with enoxaparin. Demographic information, Anti-Xa levels, dose modifications, and outcomes were abstracted using the electronic medical record (Epic®) and analyzed.

RESULTS: 103 patients had therapeutic Anti-Xa levels at the time of hospital discharge. As instructed, 82 (80%) patients returned for follow-up within 9 days of discharge, with only 59 (72%) patients having therapeutic Anti-Xa levels. Of these 59 subjects, only 34 patients returned to clinic for their 1-month follow-up visit, of which 27 (80%) had therapeutic levels requiring no dose adjustments. Of the original 59 subjects, 29 patients returned for their 2-month follow-up, of which 26 (90%) patients continued to have therapeutic levels.

CONCLUSIONS: Initial therapeutic levels immediately post-discharge are critical to ensuring therapeutic dosing throughout the course of therapy. Once confirmed, the majority of subjects continued to have therapeutic levels at their 1-month (80%) and 2-month follow-ups (90%). Given the discomfort of laboratory testing, costs, and time to families, it may be reasonable to decrease the frequency of laboratory monitoring at these monthly visits.