Low-molecular-weight heparins cannot be monitored adequately by activated partial thromboplastin time, activated coagulation time, whole-blood clotting time, or thrombin time because of their high ratio of anti-Xa to anti-IIa activities. A prolonged activated partial thromboplastin time is indication of overdose; therefore an anti-Xa assay should be employed.
For deep vein thrombosis prophylaxis 2500 IU is given subcutaneously every 12 h. For anticoagulation of an extracorporeal circuit a bolus of 35 IU/kg is given intravenously followed by an infusion of 13 IU/kg. The dose is adjusted to maintain anti-Xa activity at 0.5 to 1 IU/ml (or 0.2 to 0.4 IU/ml if there is a high risk of hemorrhage).
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