Heparin therapy
Administration and dosage
Low molecular weight heparin (LMWH)
There is increasing use of fractionated LMWH due to their efficacy in DVT and thromboembolic disease, rapid stabilisation of anticoagulant effect, greater predictability and reduced risk of bleeding complications. Caution is advised in renal failure, when measurement of anti Xa is advisable (0.6-1.0 u/ml at peak, i.e. at 3hrs).
Prophylaxis of thromboembolic disorders
Use low molecular weight heparin (Enoxaparin-Clexane), advantageous in that it requires only one injection daily and no monitoring is required.
Major surgery over age 40 yrs, obesity, malignancy or previous history of DVT or PE.
Dosage:
Pre-operative - 2 hrs before, 2000 i.u. (20mgs) sub-cutaneously, then
post-operatively - 2000 i.u. (20mg) sub-cutaneously daily for 7-10 days or until risk of thromboembolism has diminished.
Orthopaedic surgery and higher risk patients - 4000 i.u. (40mgs) daily starting dose 12 hrs before surgery then every 24 hrs for 7-10 days post-operatively.
Care of the elderly - 2000-4000 i.u. (20-40mgs), depending on risk (Enoxaparin-Clexane); longer-term heparin or oral anticoagulants may be required in certain risk cases. Consultant Haematologist will advise.
Prophylaxis in pregnancy
Previous history of DVT or PE or known thrombophilia. Cannot use warfarin in first trimester. it is teratogenic must use Low Molecular Weight Heparin (LMWH).
Warfarin may be substituted for heparin from 16-36 weeks, maintaining the INR between 2.0 and 3.0, although CNS abnormalities have been reported during this period and many authorities advocate Heparin throughout pregnancy in spite of the risk of osteoporosis (which is small). Management around the time of delivery should be discussed between consultant obstetrician and consultant haematologist. Higher dosage of Heparin is necessary in prosthetic heart valves and thrombophilia. Monitor the anti Xa level if necessary at 0.6-1 u/ml at peak, 3 hours after injection.
Treatment of thromboembolic disorders
Unstable angina and non ST elevation wave myocardial infarction
Enoxaparin 1mg/kg s.c. twice daily using pre-filled graduated syringes of 60, 80 or 100mg. If reversal is required due to bleeding, standard doses of protamine apply, i.e. 1mg/100u heparin within 15 mins: half-life of unfractionated heparin (based on anti Xa effect) is 1-2 hrs, of Enoxaparin 4hr, Tinzaparin 2hr.
Deep vein thrombosis and pulmonary embolism
Enoxaparine 1.5mgs/kg daily until oral anticoagulation control is established (at least 5 days).
Treatment of thromboembolism during pregnancy
Women should have clexane 1mg/kg BD to start with should ave levels checked within 1 week then patients should have full dose Clexane (1.5mg/kg, 150u/kg) every 24 hours. Measure pre- and 3 hour post-dose anti Xa which should be between 0.3 and 0.7 u/ml. It is very important to continue anticoagulation for at least six weeks post delivery. This may be wit LMWH or warfarin. Liaise with consultant haematologist for further advice. Continue for 6 months in total.
Unfractionated Heparin - intravenous infusion
Loading dose of 5,000 i.u., followed by 1,000 - 2,000 i.v./hr (approx. 15-30 i.u. per kg/hr), i.e. 30-40,000 i.u./24hours. Daily monitoring is advised. Also, an initial specimen should be taken after the first 4-6 hours of infusion. Give an additional 5,000 i.u., i.v. bolus if the first 4hr APTT ratio is less than 1.2.
Parenteral therapy should continue until oral anticoagulants have achieved a therapeutic effect (2-4 days) or longer in massive PE or ileofemoral thrombosis. Using the APTT ratio aim for 1.7 - 3.2 times control.
Heparin resistance - increasing rather than decreasing requirement may indicate development of heparin resistance.
Heparin induced thrombocytopenia - the development of Heparin antibodies from 5-14 days after starting, may result in thrombocytopenia and thrombosis. Please monitor platelet count from 5 days onward. Stop Heparin if the platelet count falls by 50%; send 10mls clotted blood for Heparin antibodies. Note this process in patients recently exposed to Heparin. check platelet count earlier in this group.
Reversal of Heparin - in association with excess bleeding for advice contact consultant haematologist.