Dalteparin

Dalteparin sodium is a **low molecular weight (fractionated) heparin (LMWH)** used primarily for the prevention and treatment of thromboembolic diseases. * **Mechanism Advantage**: Unlike unfractionated heparin (UFH), LMWHs like dalteparin have a more predictable pharmacokinetic profile and preferentially target Factor Xa over thrombin, reducing the risk of spontaneous hemorrhage. * **Veterinary Challenges**: While highly effective in humans with once or twice daily dosing, dogs and especially cats eliminate dalteparin very rapidly. This necessitates frequent subcutaneous injections (up to every 4-6 hours in cats), which can make long-term outpatient management highly impractical and expensive. * **Clinical Utility**: Often utilized in critical care settings for patients at high risk of thrombosis (e.g., immune-mediated hemolytic anemia, protein-losing nephropathy, feline aortic thromboembolism, or equine colic).

กลไกการออกฤทธิ์: Dalteparin exerts its anticoagulant effect by binding to and accelerating **antithrombin III (ATIII)**. * **Conformational Change**: Binding induces a conformational change in ATIII, significantly accelerating its ability to inactivate coagulation factors. * **Factor Xa Selectivity**: Because dalteparin consists of shorter polysaccharide chains (average molecular weight ~5000 daltons) compared to unfractionated heparin, it lacks the chain length required to simultaneously bridge ATIII and thrombin (Factor IIa). Therefore, it preferentially inhibits **Factor Xa**. * **Pathway**: Dalteparin + ATIII → **Potent inhibition of Factor Xa** → Decreased conversion of prothrombin to thrombin → Prevention of fibrin clot formation. *Clinical Pearl*: Because it minimally impacts thrombin, routine clotting times like TT or aPTT are usually unaffected and are poor monitoring tools for this drug.

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