Antithrombotic Agents

Heparin Therapy

Heparin mediates its activities through catalysis of the natural inhibitor AT. The activities of heparin are considered anticoagulant and antithrombotic. The antithrom-botic activities of heparin are influenced by plasma concentration of AT. In the presence of heparin, thrombin generation is decreased in young children compared to adults. Clearance of heparin is also faster in the young. For this reason the optimal dosing of heparin is different in children from adults. In pediatric patients APTT values correctly predict heparin therapy only 70% of the time. The following dosage schedule is utilized for heparinization:

• Loading dose: 75 units/kg IV over 10 minutes

• Initial maintenance dose:

<1 year of age: 28 units/kg/h >1 year of age: 20 units/kg/h

• Repeat APTT 4 hours after administration of the heparin loading dose and monitor heparin dose to maintain an APTT at 2.5 times normal for the reference laboratory as follows:

APTT times of normal

Bolus (units/kg)

Dose change (units/kg/hour) (increase or decrease of bolus dose)

Intervals of testing APTT (hours)

<2

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