Heparin and Warfarin - Sydney South West Area Health Service

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Sydney South West Area Health Service Guideline No: SSW_GL2007_010 Date issued: November 2007 Notes: Based on creatinine clearance calculated using the COCKCROFT – GAULT EQUATION • Estimate calculated creatinine clearance rate (eCl CR ) = (140-age) x weight in kg 0.814 x creatinine in umol/l Multiply the result by 0.85 for females. These estimates of Glomerular Filtration Rate (GFR) are unreliable in very obese or oedematous patients. Formal assessment of renal function is recommended in these patients. 3. Management of Bleeding on Intravenous Standard and Low Molecular Weight (LMW) Heparin 3.1 Intravenous Unfractionated Heparin • For bleeding which is non-life threatening, heparin can be ceased. Given the short half-life of 60 minutes, there will be rapid normalisation of the aPTT within 2-3 hours. • For potentially life threatening bleeding, administration of protamine may be appropriate. 50 mg protamine will neutralise 5,000 units of heparin, and would be the appropriate dose if the patient has received a bolus in the last hour. For infusions of heparin, give 30 mg protamine for a typical infusion rate of 1250 units/hour (30,000 units per 24 hours), with proportionately more or less for the actual infusion rate. 3.2 Low Molecular Weight (LMW) Heparin • Neutralisation of LMW heparins is incomplete with protamine, with neutralisation of only ~ 60% of the anti-Xa activity occurring. • The suggested dosage of protamine is 1 mg protamine for each 100 anti- Xa units of LMW heparin (1 mg Enoxaparin = 100 anti-Xa units) given in the previous 8 hours. A second dose of 0.5 mg protamine per 100 units of LMW heparin can be considered if severe bleeding continues. • If the last dose of LMW heparin was > 8 hours, a smaller dose should be given (e.g. 0.5 mg protamine per mg of Enoxaparin). • Protamine may not be beneficial if the last dose of LMW heparin was > 12 hours ago and renal function is normal. 3.3 Precautions with protamine: • Excess protamine may have an anticoagulant effect and should be avoided. • Adverse reactions may occur including anaphylaxis, hypotension, dyspnoea and bradycardia. Fatal reactions have been reported. Protamine should be administered slowly over 10 minutes. Adverse reactions are said to be more common in insulin dependent diabetics, patients who have had previous vasectomy, and those with fish allergies. These patients should be pre-medicated with Phenergan 12.5 mg IVI and hydrocortisone 100 mg IVI. Compliance with this guideline is recommended Page 10 of 24
Sydney South West Area Health Service Guideline No: SSW_GL2007_010 Date issued: November 2007 Reference: Hirsh J & Raschke R. The Seventh ACCP Conference on antithrombotic and thombolytic therapy. Chest 2004; 126: 188S-203S Enoxaparin prescribing information (Aventis Pharma Ltd) via MIMS Online, July 2006 4. Initiation of Warfarin Therapy 4.1 Before Starting Treatment Check baseline INR, PT, aPTT, FBC and LFTs. A pregnancy test is recommended in women of childbearing age. 4.2 Commencement of Therapy Assess that the benefit outweighs the risk. Risk factors for bleeding include: • Age over 65 years (especially the frail). • Recent surgery and antibiotic therapy. • Weight less then 50 kg. • Concomitant drugs inhibiting warfarin metabolism (see below). • Poor diet. • Any other bleeding risks. • Patients with abnormal liver function tests. Guidance should be sought from Senior Medical Staff if there is any uncertainty or if there are multiple risk factors for prescribing anticoagulant medication. If no risk factors exist and the patients does not have a previous known stable dose: Commence therapy at 5 mg daily with daily INR monitoring. This will attain INR of approximately 2.0 in 4-5 days. If no risk factors exist and the patient has a previous known stable dose of Warfarin: Recommence on the same dose that the patient previously had a stable therapeutic INR, assuming that no new risk factors exist. No “loading” dose is required in this situation. If risk factors exist (see above): A reduction of the commencement dose to 3mg daily should be considered, if the patient has never taken Warfarin, and reduction from the previous known stable dose by 1-2 mg, if the patient has previously taken Warfarin. Warfarin dose should usually be charted at 4 PM for inpatients (morning INR ~ 16 hours after a dose), depending on the timetable of the individual ward. For outpatients the timing of Warfarin dosing may be left to patient and physician preference. • Warfarin may be commenced on day 1 or 2 of heparin therapy. • Overlap warfarin with heparin (LMWH or UFH): The consensus guidelines suggest a minimum 5 days of heparin therapy, with four days of overlapped heparin plus Warfarin. Compliance with this guideline is recommended Page 11 of 24
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Heparin and Warfarin - Sydney South West Area Health Service

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