Low molecular weight heparin

Background

A class of anticoagulant medications. These drugs are used for treating deep vein thrombosis, pulmonary embolism when it is located in the veins, or heart attacks and strokes when located in the arteries. LMWHs cannot be acceptably measured using the partial thromboplastin time (PTT) or activated clotting time (ACT) tests. Rather, LMWH therapy is monitored by the anti-factor Xa assay, measuring anti-factor Xa activity.

Types

LMWH	Average molecular weight	Ratio anti-Xa/anti-IIa activity
Bemiparin	3600	8.0
Nadroparin	4300	3.3
Reviparin	4400	4.2
Enoxaparin (Lovenox)	4500	3.9
Parnaparin	5000	2.3
Certoparin	5400	2.4
Dalteparin	5000	2.5
Tinzaparin	6500	1.6

Differences from unfractionated heparin

Differences from heparin (i.e. "unfractionated heparin") include:

• Average molecular weight: heparin is about 15 kDa and LMWH is about 4.5 kDa.
• Less frequent subcutaneous dosing than for heparin for postoperative prophylaxis of venous thromboembolism.
• Once or twice daily subcutaneous injection for treatment of venous thromboembolism and in unstable angina instead of intravenous infusion of high dose heparin.
• No need for monitoring of the APTT coagulation parameter as required for high dose heparin.
• Possibly a smaller risk of bleeding.
• Smaller risk of osteoporosis in long-term use.
• Smaller risk of heparin-induced thrombocytopenia, a potential side effect of heparin.
• The anticoagulant effects of heparin are typically reversible with protamine sulfate, while protamine's effect on LMWH is limited.
• Has less of an effect on thrombin compared to heparin, but about the same effect on Factor Xa.

Indications

• DVT
• PE
• NSTEMI
• STEMI

Background

Enoxaparin (Lovenox)

1. Similar mechanism of action as heparin but with predictable effect
2. LMWHs are defined as heparin salts having an average molecular weight of less than 8000 Dalton. LMWHs inhibit the coagulation process through binding to antithrombin which in turn inhibition activated factor X.
3. Advantages over unfractionated heparin:
   1. More reliable level of anticoagulation
   2. No need for monitoring w/ PTT
   3. Decreased incidence of HIT
   4. Can give as oupt
4. Disadvantages compared to unfractionated heparin:
   1. Renally excreted; may accumulate in pts w/ renal impairment leading to bleeding
   2. Longer half-life

Dosing

1. Renal impairment (Cr clearance <30)
   1. Use 50% of usual dose or use UFH instead
2. Obesity
   1. Weight-based dosing safe up to 190kg (no data available thereafter)

Indications

• DVT
• PE
• NSTEMI
• STEMI

Complications

1. Bleeding
   1. Less common than with UFH
   2. Treatment
      1. Protamine
         1. Does not completely reverse LMWHs
         2. Carries significant anaphylaxis risk (0.2%); only use for major bleeding
         3. Dosing
            1. For Enoxaparin: protamine 1mg IV for every 1mg of enoxaparin given in previous 8h
               1. If 8–12h since last enoxaparin dose give 0.5mg IV for every 1mg of enoxaparin given
2. Pruritus
3. Local skin reaction

See Also

• Heparin (Unfractionated)
• Coagulopathy (Main)