Low molecular weight heparin (LMWH)

Low molecular weight heparin (LMWH)

In infants and children, the LMWH of choice at Starship is enoxaparin (Clexane®).

In patients with renal impairment it may be advisable to check the anti-Xa levels prior to surgery. Discuss with a senior medical officer.

Indications

Treatment and prophylaxis of venous thromboembolism such as deep vein thrombosis, pulmonary embolism and sinus venous thromboses.

The decision to use LMWH instead of standard/unfractionated heparin or warfarin depends on the clinical scenario and individual patient factors such as bleeding risk or ease of venous access.

Prescription and Administration

• Obtain baseline FBC, APTT, PT and renal function prior to commencing.
  

• Timing of commencement, and duration of therapy, should be individualised and discussed with a paediatric haematologist.
  

• The prescribed dose should be calculated according to the table below, depending upon the patient’s age and whether LMWH is indicated for the treatment or prevention of thrombosis.

Dose

Round dose to the nearest prefilled syringe size where able (20 mg, 40 mg, 60 mg, 80 mg, 100 mg, 120 mg, 150 mg available).

♦ Require 50% larger doses possibly due to larger volume of distribution and/or reduced antithrombin levels.

# Prophylactic LMWH: Further studies are required to define the highest risk groups in paediatrics and the potential benefits of prophylaxis but in the absence of such data prophylaxis should be considered on an individual basis, particularly in older children with multiple recognised risk factors.

Administration

LMWH is administered via the subcutaneous route (SC). This can be achieved by either rotating injection sites or by injecting into a subcutaneous injection port.

Direct subcutaneous injection should be given into a subcutaneous tissue skinfold of the abdomen or the upper-outer aspect of the thigh. The skinfold should be held throughout the injection. After removal of the needle, do not rub the site. Rather, place firm, even pressure to the site of injection for 1-5 minutes. This aids in minimizing the size of the bruise that may develop at the injection site.

To enable multiple injections without repeatedly puncturing the skin, Enoxaparin can be administered via the I-Port Advance injection port in infants and children with sufficient subcutaneous tissue.

I-Port Advance subcutaneous device and Unisharp 31G x8mm syringe/needle (pink)

1. Select appropriate enoxaparin syringe (e.g. 20mg/0.2mL, 40mg/0.4mL or 60mg/0.6mL) for dose required.

2. Remove the plunger from the Unisharp syringe.

3. Add the contents of the enoxaparin to the Unisharp syringe.

   1. Aim the enoxaparin needle at the side of the Unisharp syringe when instilling to reduce the number of potential air bubbles. (The narrow syringe makes the Clexane more viscous with development of air bubbles which are difficult to disperse resulting in loss of medication).

   2. Replace the syringe plunger and select desired dose (mg) by discarding enoxaparin until the plunger reaches the equivalent dose in mL.

      • The Unisharp syringe is 0.3mL with 0.01mL increments allowing administration of small volumes without requiring dilution

      • To administer doses greater than 30mg (0.3mL), prepare 2 syringes.

Direct subcutaneous injection

There are no graduations on the 20 mg /0.2 mL and 40 mg/0.4 mL prefilled syringe therefore to administer any doses less than 20 mg or between 21 and 39 mg see below:

1. To administer a dose less than 10 mg:

   • Draw 0.8 mL sodium chloride 0.9% into a 2 mL syringe and then pull the plunger back to 1.1 mL (this will allow for excess air to be expelled).

   • Remove the needle cap from the enoxaparin 20 mg/0.2 mL prefilled syringe and inject the contents into the sodium chloride 0.9% syringe and mix well.

   • This gives a concentration of 20 mg/ mL.

   • Verify the dose required and discard the excess volume.

2. To administer a dose between 10 mg and 20 mg:

   • Obtain a 1 mL syringe and pull the plunger back to the 0.3 mL mark (this will allow for excess air to be expelled).

   • Remove the needle cap from the enoxaparin 20 mg/0.2 mL prefilled syringe and inject the contents into the 1 mL syringe.

   • Verify the dose required and discard the excess volume.

3. To administer a dose between 21 mg and 39 mg, use a 60 mg/0.6 mL graduated prefilled syringe and discard excess volume.

Monitoring and adjusting LMWH (Treatment)

Ensure the sample is not taken from a heparin contaminated line.

Obtain anti-Xa assay 3.5-4 hours post morning dose and adjust as follows:

• The APTT does not give any indication about degree of anticoagulation with LMWH.

• A platelet count should be obtained weekly for the first month. If there is an abrupt decrease in platelet count (approximately 50%) consider heparin induced thrombocytopaenia (HIT) and discuss with paediatric haematologist.

Note:

• Avoid IM injections and arterial puncture during anticoagulant therapy. When such procedures are clinically necessary, ensure adequate external pressure is applied post-procedure.

• Avoid aspirin and other anti-platelet medications unless directed otherwise as this can potentiate the anticoagulant effect of LMWH.

For monitoring of LMWH (Prophylatic) please discuss with paediatric haematologist.

Complication

The major adverse event related to treatment with LMWH is bleeding. If a patient on LMWH develops a major bleed, withhold further doses and seek an urgent paediatric haematology consult.

Rarely, LMWH therapy can cause alopecia. The extent of hair loss can vary greatly. All cases of LMWH-related alopecia have resolved upon cessation of therapy.

The antidote for LMWH is Protamine sulphate. This reverses most, but not all, of the effects of LMWH. The dose of protamine sulphate given is dependent upon the dose of LMWH administered and the time of administration. Protamine is only prescribed in consultation with paediatric haematologist or intensivist. Protamine is administered by slow IV infusion (over 10 mins) to avoid a hypotensive reaction.