Antithrombin Concentrate in Pediatric Patients Requiring Unfractionated Heparin Anticoagulation

OBJECTIVE: To describe antithrombin levels, altered unfractionated heparin effect (anti-factor Xa activity and activated partial thromboplastin time), and adverse effects post administration of a single high dose of antithrombin concentrate. DESIGN: Retrospective review. PATIENTS: Infants and children with antithrombin levels less than 50% and a subtherapeutic unfractionated heparin effect. SETTING: Quaternary care children's hospital with a dedicated anticoagulation program. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: A single high dose of antithrombin concentrate was administered. Antithrombin level, anti-factor Xa, and activated partial thromboplastin times were measured post antithrombin concentrate infusion and daily until stable. One hundred twenty-one patients received 246 doses of antithrombin. Patients were described using two cohorts based on the ability to obtain exact heparin doses. Cohort 1 included all patients between January 2004 and May 2008 when complete heparin dosing was unavailable. Cohort 2 included patients from May 2008 to May 2011 when heparin dose was available. Median age and weight were 3.7 months and 4.1 kg. Mean antithrombin concentrate dose was 222 IU/kg. Mean antithrombin level increased from 0.39 to 1.20 U/mL following antithrombin concentrate administration. In cohort 2, unfractionated heparin doses to achieve a target anti-factor Xa activity pre-post antithrombin concentrate were 28 and 19 U/kg/hr, respectively, for children 12 months old or younger and 25 and 19 U/kg/hr, respectively, for children older than 12 months. There were no hemorrhagic, thrombotic, or allergic events within 1 week of antithrombin concentrate administration. CONCLUSIONS: This is the largest study of antithrombin concentrate evaluation in children. Administration of antithrombin concentrate increases anti-factor Xa activity with lower administered unfractionated heparin doses.