Low MolecularWeight Heparin

The anticoagulant activities of low-molecular-weight heparin (LMWH) are also mediated by catalysis of the natural inhibitor AT. LMWHs preferentially inhibit factor Xa over thrombin due to the decreased capacity to bind both AT and thrombin simultaneously for thrombin inhibition. Preparations used for children are enoxa-parin (Lovenox; Rhone-Poulenc) and reviparin (Cloverine, Knoll Pharma). Young infants have an accelerated clearance of LMWH compared to older children.

Indications for Low-Molecular-Weight Heparin Therapy

• Patients requiring anticoagulation and deemed to be at orrhage

• Patients in whom venous access for administration and heparin therapy is difficult.

Dose (Enoxaparin) [Lovenox, Aventis]

Age (months)

Treatmenta (dose)

Prophylactic (dose)


1.5 mg/kg every 12 h SC

0.75 mg/kg every 12 h SC


1.0 mg/kg every 12 h SC

0.5 mg/kg every 12 h SC

Abbreviation: SC, subcutaneously. aMaximum dose, 2.0 mg/kg every 12 h.

Abbreviation: SC, subcutaneously. aMaximum dose, 2.0 mg/kg every 12 h.

Monitoring of Low-Molecular-Weight Heparin Therapy

• Prior to the initiation of LMWH therapy, a complete blood count, including platelet count, PT, and APTT, should be determined.

• Aspirin or other antiplatelet drugs should be avoided during the therapy.

• Intramuscular injections and arterial punctures should be avoided during the therapy.

• If the platelet count drops to 100,000/mm3 or less, heparin-induced thrombocy-topenia (HIT) must be ruled out; it rarely occurs with LMWH therapy.

• The pretreatment anti-factor Xa level should be determined; thereafter, weekly monitoring should be sufficient 4-6 hours after the SC administration of LMWH.

increased risk for hem-monitoring of standard

The therapeutic anti-factor Xa level is 0.5-1.0 units/mL and the prophylactic anti-factor Xa level is 0.1-0.3 units/mL.

• For long-term LMWH therapy, bone densitometry studies should be performed at baseline and then at 6-month intervals to assess for possible osteoporosis.

Duration of Low-Molecular-Weight Heparin Therapy

• LMWH is usually administered up to 3 months without warfarin.

• Extensive thrombus or pulmonary embolus. LMWH for 7-14 days should be administered and warfarin should be started on day 5.

• Newborns may be treated for 10-14 days with LMWH alone.

Adjusting Low-Molecular-Weight Heparin Dose

The dose of LMWH can be adjusted according to the anti-factor Xa level achieved:

Anti-factor Xa level (units/mL)a



25% increase


10% increase

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