Low-molecular-weight heparin (LMWH) is derived from standard heparin through either chemical or enzymatic depolymerization. Whereas standard heparin has a molecular weight of 5000 to 30 000 Daltons, LMWH ranges from 1000 to 10 000 Daltons. LMWH binds less strongly to protein, has enhanced bioavailability, interacts less with platelets and yields a very predictable dose response. The clinical advantages of LMWH include predictability, dose-dependent plasma levels, a long half-life and less bleeding for a given antithrombotic effect. Thrombocytopenia is not associated with short-term use of MLWH. LMWH is administered once or twice daily, both during the high-risk period when prophylaxis for DVT is recommended and also while waiting for oral anticoagulation to take effect in the treatment of DVT. The activated partial thromboplastin time does not need to be monitored, and the dose does not need to be adjusted (Rydberg et al. 1999).
Danaparoid sodium (Orgaran) is an alternative anticoagulant for patients who develop heparin-induced thrombocytopenia from heparin therapy. Danaparoid is a low-molecular-weight heparinoid. Its active components consist of heparan sulfate, dermatan sulfate and chondroitin sulfate. The major difference between danaparoid and other LMWHs is that danaparoid is devoid of heparin or heparin fragments. However, it exerts effects similarly to other LMWHs; Danaparoid acts by inactivating thrombin.
Table 4. Generic and Trade-names of Low Molecular Weight Heparin
The most commonly studied LMWH for the prophylaxis of venous thromboembolism post SCI is enoxaparin, which was the first used in the USA. The drug has a plasma half-life of 4.4 hours compared with 0.35 hours for LDUH and its subcutaneous bioavailability is 50%, compared to 20% for LDUH (Tomaio et al. 1998). In a meta-analysis, Paciaroni et al. (2008) compared the effectiveness of LDUH to that of LMWH in reducing DVT incidence in individuals post SCI. The study found no significant reduction in DVT between the LDUH group and the control group, or the LDUH group and the LMWH group. However, LMWH was reported to significantly reduce the rate of PE (p=0.04).