2025 Southeastern Residency Conference

Title:  Optimal Enoxaparin Dosing in Children with Congenital Heart Disease Less than 1 Year of Age 


Authors: Katelyn Price, Hania Zaki, Haseena Hussain, Jennifer Sterner Allison, Helen Giannopoulos, Gary Woods, Josh Branstetter 


Objective: Evaluate enoxaparin dosing regimens in children with congenital heart disease in patients less than 1 year of age. 


Self Assessment Question: 
Which of the following enoxaparin dosing strategies would be best to use to acheive initial therapeutic levels quicker based on the results of this study?
A. 0.75 mg/kg q12h
B. 1 mg/kg q12h 
C. 1.5 mg/kg q12h
D. 1 mg/kg q24h 


Background: Venous thromboembolism (VTE) prevalence amongst pediatric patients with congenital heart disease has increased over the years. Enoxaparin’s pharmacokinetic properties and less intensive monitoring parameters make it a desirable treatment option. Currently, reported enoxaparin dosing strategies and their correlation to therapeutic anti-Xa levels are variable for infants aged 2 to 12 months.  


Methods: This was a single center, retrospective, quasi-experimental study conducted between January 2008 and June 2023 in patients receiving therapeutic enoxaparin. Patients were divided into pre (January 2008 to December 2014) and post (June 2020 to June 2023) intervention groups, with the pre-intervention group receiving an enoxaparin dosing regimen of 1 mg/kg every 12 hours (standard dose) and post-intervention group receiving an enoxaparin dosing regimen of 1.5 mg/kg every 12 hours (high dose). Patients were included if they were between the ages of 2 to 12 months of age, admitted to the heart center, and had at least one heparin assay drawn 4-6 hours after a dose. Patients were excluded if they had thrombocytopenia defined as platelets at baseline less than 100,000 plts/µL, poor renal function defined as a creatinine clearance less than 30 ml/min, or an anti-xa goal other than 0.5 - 1 unit/ml. The primary objective was to evaluate the percent of patients who achieved initial target anti-xa levels. Secondary objectives included time to target anti-Xa level, number of dose changes needed to obtain goal anti-xa levels, and bleeding.


Results: A total of 85 patients were included in this study, 33 in the standard dose group and 52 in the high dose group. The median age was 3.73 months (IQR 3.01 to 6.53) in the standard group and 4.18 months (IQR 3.08 to 5.76) in the high dose group. There were similar demographics between both groups with the exception of more Black or African American (29 (56%) vs 8 (24%); p = 0.003) patients in the high dose group. More patients in the high dose group achieved initial therapeutic levels of enoxaparin (36 (69%) vs 5 (15%); p < 0.001).  The time between initial dose of enoxaparin and first therapeutic anti-Xa level was longer in the standard dose group compared to the high dose group, respectively (87 hrs (IQR 41 to 112) vs 24 hrs (IQR 16 to 40; p< 0.001)).  There was no difference in the incidence of minor bleeding (6 (18%) vs 5 (6%); p = 0.084) or major bleeding (1 (3%) vs 7 (13%); p = 0.14) between the standard and high dose groups, respectively. 


Conclusion: High dose enoxaparin in infants with congenital heart disease resulted in a higher percentage of initial anti-Xa target attainment and a decreased time to target anti-Xa level. There was no difference in minor or major bleeding between the standard and high dose strategies. Based on our findings, it is safe and effective to dose enoxaparin higher in infants with congenital heart disease.