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). Several types of LMWH are available (Table 5).
Danaparoid sodium (Orgaran) is an alternative anticoagulant for individuals 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.
The most commonly studied LMWH for the prophylaxis of VTE post SCI is enoxaparin, which was the first used in the United States. 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).
Discussion
Several studies have examined the independent thromboprophylactic effectiveness of LMWH on the incidence of DVT and PE in acute SCI. Various forms of LMWH have been investigated including Enoxaparin, Dalteparin, and Tinzaparin.
Two studies compared the effectiveness of Enoxaparin versus Dalteparin in preventing VTEs. Chiou-Tan et al. (2003) conducted an RCT in which acute SCI individuals (<3 months post-SCI) were randomized to receive either 30 mg Enoxaparin every 12 hours or 5000 IU Dalteparin once daily. The authors found that 6% of individuals receiving Enoxaparin and 4% of individuals receiving Dalteparin developed DVTs (p=0.51); however, no individuals developed PE. A case control study conducted by Slavik et al. (2007) also compared the efficacy of Enoxaparin and Dalteparin. Individuals were studied within 72 hours post-SCI and received either 30 mg Enoxaparin twice daily or 5000 IU Dalteparin once daily. No significant difference regarding the incidence rate of DVT or PE was found between these groups, indicating equivalent prophylactic efficacy.
A case control study by Marciniak et al. (2012) compared the effect of Enoxaparin versus Tinzaparin on incidence of VTE events. All individuals were within 3 months of sustaining an SCI and were admitted to inpatient rehabilitation at a median of 15 days after injury. Individuals received either 5000 IU Enoxaparin, 4500 IU Tinzaparin (high-dose), or 3500 IU Tinzaparin (low-dose). The results revealed that individuals who received either Enoxaparin or the high dose of Tinzaparin had a significantly reduced risk of developing VTE complications compared with individuals receiving 3500 IU Tinzaparin. The authors indicated that uncontrolled factors may have affected this result, although these were not specified. The findings suggested an association between developing VTE and having had no prophylaxis prior to admission to inpatient rehabilitation, despite using prophylaxis after admission. Prophylaxis prior to admission may be protective of VTE, with no particular type of prophylaxis being significantly different in terms of protective efficacy.
A case control study by Hebbeler et al. (2004) compared two dosages of Enoxaparin. Individuals were within 2 months of sustaining SCI and received either 40 mg once daily or 30 mg twice daily of Enoxaparin. There were no significant differences found in DVT or PE incidence between groups and therefore the prophylactic efficacy of Enoxaparin was equivalent between the two dosages studied.
In a case series by Harris et al. (1996), individuals who were hospitalized for an average of 19 days following injury received 30 mg of Enoxaparin every 12 hours from admission. No individuals developed DVT in this study population. In a recent observational study, DiGiorgi et al. (2017) found that just 6.1% of their sample experienced a DVT and 4.1% a PE after 40 mg daily enoxaparin administration.
One systematic review evaluated the ideal time for initiating DVT treatment with LMWH. Christie et al. (2011) concluded that LMWH prophylaxis for DVT should be administered within 72 hours post-SCI. However, this conclusion should be interpreted with caution, as it was based on a single, small (N=5) systematic review.
Conclusion
There is level 1b evidence (from one RCT and one case control: Chiou-Tan et al. 2003; Slavik et al. 2007) that 30 mg twice daily Enoxaparin and 5000 IU daily Dalteparin are equally effective as prophylaxis for venous thromboembolism in acute SCI individuals.
There is level 4 evidence (from one case control: Hebbeler et al. 2004) that twice daily 30 mg Enoxaparin is equally as effective as 40 mg daily Enoxaparin as prophylaxis for venous thromboembolism in acute SCI individuals.
There is level 4 evidence (from two observational studies: DiGiorgio et al. 2017; Harris et al. 1996) that 40 mg daily enoxaparin is effective in reducing risk of thromboembolism.
