Enhances the binding of antithrombin III to factors IIa, IXa, Xa and XIIa.
Only effective if adequate AT-II present.
May also inactivate thrombin and block conversion of fibrinogen to fibrin.
The inhibition of factor XII activation prevents the formation of stable fibrin clots.
Does not significantly change the concentrations of clotting factors, nor does it lyse pre-existing clots.
Indications
Given to promote anticoagulation.
Primary uses in small animal medicine include the treatment of disseminated intravascular coagulation (DIC) and thromboembolic disease, and the maintenance of IV catheter patency. Use in DIC is controversial and information on efficacy is lacking.
100-200 units/kg IV initially; may repeat in 4 hours, then adjust dose prn and repeat SC TID. Provision of fresh or frozen plasma is required in anti-thrombin III deficient animals for heparin to be effective.
For the successful treatment of DIC heparin therapy is only one aspect. Addressing the precipitating cause, administration of fluids, blood, aspirin and diligent monitoring of coagulation tests (activated partial prothrombrin time (APTT) , OSPT ), fibrin degradation products and fibrinogen are all important factors.
For treatment of thromboembolic disease
100-200 u/kg IV as a loading dose, followed by 200-300 u/kg SC TID-QID; adjust dosage so APTT is 1.5-2.5 times normal.
The doses of heparin are controversial with some texts recommending higher doses or the use of constant IV infusions.
Use in DIC is controversial and information on efficacy is lacking.