Heparin

Heparin is a potent anticoagulant. It is a hetogeneous mixture of sulfated polysaccarides which bind to enfothelial cell surfaces.

Uses

 

Mechanism

Heparin's actions depends on antithrombin III, which inhibits pro-coagulant proteases by binding with them in 1:1 ratios. In the absence of heparin these reactions are slow. Heparin accelerates them by 1000x by inducing a conformational change in AT III, exposing its active site and facilitating its binding with clotting factors.

Heparin acts as a catalyst to increase AT III binding with proteases. Once this binding has occurred, heparin is released to bind furhter AT III molecules.

 

Types

 

Unfractionated

Regular, high molecular weight heparin (HMWH) is shorter acting, cheaper.

Can be stopped as it's on a drip. Can be reversed with protamine, though be cautious, as too much protamine acts as an anticoagulant.

 

Low molecular weight heparin (Enoxaparin, dalteparin)

LMWH inhibits activated factor X, but has less activity on AT III. They are effective in preventing DVT postoperatively, in the treatment of acute coronary syndromes, and fir acute venous thromboembolic disease.

LMWH have increased bioavailability and less frequent dosing (1-2x daily).

INR/PTT does not change with LMWH.

 

 

 

 

 

Dose and Half Life

 

 

return to top

 

 

Adverse Drug Reactions

The major adverse effect of heparin in bleeding, with a ~ 3% risk of hemorrhage.

 

Heparin-induced thrombocytopenia (HIT), occurring by inducing platelet activation and aggregation, occurs in ~25% of patients. It can be severe in 5% of people. It can occur with any form or route of administration, though is less common with LMWH.

 

return to top

 

 

Counter-Indications and Drug Interactions

Heparin is contraindicated in patients with:

return to top

 

 

Metabolism and Excretion

return to top