Warfarin. Starting warfarin. Monitoring INR

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1 Blood thinner (anticoagulant) used to stop blood clotting in people with mechanical heart valves, some clotting disorders (thrombophilias), some heart disease, eg AF Can cause life-threatening bleeding patient education important INR (international normalised ratio) Blood test used to monitor blood levels and adjust doses. Shows average warfarin dose over last 5 days High INR usually means warfarin dose needs to be reduced Low INR usually means warfarin dose needs to be increased Target INR As recommended by physician, cardiologist, cardiothoracic surgeon If mechanical mitral valve, some older mechanical aortic valves If newer mechanical aortic valve, tissue (bioprosthetic) valve, other conditions, eg DVT, AF, pulmonary embolism Starting warfarin Only start on medical advice Need to be able to monitor daily for first week, then regularly Follow Table 6.24 (p421) If INR not more than 1.5 by day 6 specialist consult Monitoring INR Use previous INR-readings and corresponding warfarin doses to guide what warfarin dose will give target INR After starting doses (first 6 days) need twice weekly testing for 4 weeks or until stable (stays in therapeutic range for 2 weeks) If stable weekly testing for 4 weeks, then monthly More frequent monitoring if Warfarin dose adjusted or change in INR over short time Stopped or started other medicine, especially if interacts with warfarin Person doesn't take warfarin regularly Other medicines Warfarin interacts with many medicines, some increase bleeding, others increase clotting If starting new medicines, including over the counter, eg aspirin, NSAIDs Check for possible interactions with warfarin Watch INR levels closely, warfarin dose may need to be adjusted 420

2 Table 6.24: Warfarin starting doses for adults Day INR Warfarin dose 1 5mg Adjusting warfarin 5mg mg mg More than mg mg mg 10mg mg mg 10mg mg mg Get specialist advice mg mg Only adjust with medical consult or in line with management plan Adjustments based on target range See Table 6.25 for target range (p422) See Table 6.26 for target range (p422) Do not make dose changes on daily basis after day 6. Will make it hard to work out stable daily dose Do not 'over-correct' single borderline abnormal INR readings by changing warfarin dose Do not adjust if bleeding or embolic/thromboembolic complications medical consult General topics 421

3 Table 6.25: Warfarin dose adjustment for target range of INR Adjustment Next INR test Increase by 20% + extra dose If heart valve medical consult. May need heparin Increase No change If stable 4 weeks If not stable 7 days Decrease by 10% Decrease by 20% + miss one dose 4.5 See Elevated INR with or without bleeding (p423) Table 6.26: Warfarin dose adjustment for target range of INR Adjustment Next INR test Increase by 20% + extra dose If heart valve medical consult. May need heparin Increase No change If stable 4 weeks If not stable 7 days Decrease by 10% Decrease by 20% + miss one dose 4.5 See Elevated INR with or without bleeding (p423) Lifestyle advice Alcohol safer drinking (p232) Some foods interact with warfarin. Avoid sudden changes in amount of these foods they eat Dark green leafy vegetables Brussels sprouts, cabbage Asparagus Broccoli Prunes Avoid contact sports, eg football, rugby Avoid traditional practices that involve breaking the skin Women using warfarin should not become pregnant. Women of childbearing age need appropriate contraception (WBM p332) 422

4 Elevated INR with or without bleeding Remember: Risk of bleeding increases when INR reaches 4.5. Table 6.27 Management of elevated INR INR Low risk of bleeding High risk of bleeding* Less than 4.5 See Adjusting warfarin (p421) Measure INR Give vitamin K every 24 hours oral 2mg Resume warfarin Measure INR at reduced dose every 24 hours when INR less than 4.5 More than 10 Give vitamin K Give vitamin K oral/iv 4mg oral/iv 4mg Measure INR in Measure INR again 6 12 hours to in 6 12 hours to make sure it is make sure it is falling, then every falling, then every 24 hours 24 hours Resume warfarin at reduced dose when INR less than 4.5 Note: Injectable form of vitamin K can be taken orally. Bleeding Control bleeding (use compression if possible) Medical consult straight away about sending to hospital Think about vitamin K IV 10mg * High risk of bleeding one or more of Over 65 years Regular heavy drinker Poorly controlled, severe high BP for long time OR current BP more than 180mmHg systolic or 110mmHg diastolic Symptomatic/active peptic ulcer disease Significant liver disease, eg cirrhosis, known oesophageal or gastric varices, Child-Pugh class B/C, previous haematemesis or melaena Low white blood cell or platelet counts (less than 50x109/L), coagulation defect Taking aspirin, clopidogrel, NSAID General topics 423

5 History of haemorrhagic stoke Ischaemic stroke within last 3 months Known brain blood vessel abnormality, eg aneurysm, AV malformation Significant closed head or facial injury within last 3 months Elevated risk of falls Pregnancy Known malignant brain tumour (primary or secondary) Major surgery in last 2 weeks 424