Adjustment of dosage was originally regulated by the determination of the prothrombin time. This was replaced by the INR more than a decade ago. The INR is main¬tained at 2–3 for most cases of thrombosis. Bleeding due to oral anticoagulant activity is reversed by vitamin K1.
D. Heparin
1. Unfractionated Heparin
Heparin is a glycosaminoglycan composed of chains of alternating residues of D-glucosamine and uronic acid. Heparin has a molecular weight of 15,000 with approxi¬mately 50 monosaccharide chains.
This well known intravenous anticoagulant has been used worldwide for many years and has now been partially replaced by low molecular weight heparin (LMWH) given subcutaneously. These new preparations have shown to be as effective as unfractionated intravenous heparin. They substantially reduce hospitalization costs because patients are able to administer these agents subcutaneously at home and avoid hospitalization.
The anticoagulant activity of heparin requires a cofactor, antithrombin III. A pentasaccharide sequence randomly distributed along one-third of the heparin chains mediates the interaction between heparin and antithrombin. The heparin antithrombin complex inactivates thrombin and thus prevents thrombin-induced activation of factors V and VII.

Страницы: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12