Effect of Exogenous Antithrombin Administration on Anti-Xa Levels in Infants Treated With Enoxaparin

Determine the effect of exogenous antithrombin III administration on low molecular weight heparin anti-Xa levels in the context of enoxaparin dosing in infants.

A retrospective chart review of infants receiving concomitant antithrombin III and enoxaparin. The primary objective of this study was to determine the median change in anti-Xa level with antithrombin III supplementation. Secondary objectives were to analyze the median change in antithrombin III levels after administration of exogenous antithrombin III, the dosing of antithrombin III, and the dose of enoxaparin throughout therapy. For a safety analysis, any bleeding events were recorded.

The study included 17 patients who received a total of 33 doses of antithrombin III. The median change in anti-Xa levels in infants receiving exogenous antithrombin III was 0.2 units/mL (p < 0.001). The median dose of antithrombin III was 50 units/kg and was administered when patients were receiving a median enoxaparin dose of 1.71 mg/kg. The median increase in antithrombin III levels was 16.5% (p < 0.001).

These results demonstrated that administration of exogenous antithrombin III to infants who were being treated with enoxaparin results in a significant increase in anti-Xa levels. At this time, there is insufficient evidence to recommend routine administration of antithrombin III to infants on enoxaparin. However, antithrombin III supplementation could be considered a potential option for patients who are unable to adequately achieve therapeutic anti-Xa levels with enoxaparin alone.