Remote Primary Health Care Manuals

Warfarin

  • Anticoagulant (blood thinner) used to reduce risk of blood clotting and possible stroke in people with mechanical heart valves, some clotting disorders and some heart disease, eg atrial fibrillation AF
  • Can cause life-threatening bleeding — patient monitoring and education is important
  • Women on warfarin should not become pregnant — women of childbearing age need appropriate contraception
Red Flags — Urgent Medical Consult
  • Bleeding with international normalised ratio (INR) 4.5 or more
  • Pregnant woman

International normalised ratio (INR)

  • Blood test used to monitor risk of blood clotting and indicate if warfarin needs adjusting — shows average effect of warfarin over last 5 days
  • High INR usually means warfarin dose needs to be reduced — check for signs of bleeding
  • Low INR may mean person has not been taking their warfarin or dose may need to be increased

Target INR

  • Recommended by physician, cardiologist, cardiothoracic surgeon
  • Mechanical mitral valve, some older mechanical aortic valves, combined aortic and mitral valves — 2.5–3.5
  • Newer mechanical aortic valve, other conditions (eg DVT, AF, PE) — 2.0–3.0

Starting warfarin

  • Only start on medical advice
  • Need to be able to monitor every day for first 5 days THEN regularly as advised by doctor

Monitoring INR

  • Use POC Test — can adjust straight away if needed
  • Doctor will advise how often to monitor INR in management plan — more often at start of treatment until INR is stable (in therapeutic range for 2 weeks) 
    • May need twice weekly testing until stable then weekly for 4 weeks then monthly
  • More frequent monitoring if
    • Warfarin dose adjusted or change in INR over a short time
    • Stopped or started other medicine, especially if it interacts with warfarin
  • Always supply enough medicine to cover same dosing time frames as other regular medicines, eg DAAs
    • Do not use limited supply to get person back for testing — if they run out before coming back the test will be useless
  • Tell person to bring their medicines with them in case the dose needs changing 

Other medicines

  • Warfarin interacts with many medicines — some increase bleeding, others increase clotting
  • Check for possible interactions with warfarin before starting any new medicine — including over the counter and alternative therapies
  • If starting a new medicine — watch INR levels closely. Warfarin dose may need to be adjusted

Adjusting warfarin

Method for adjusting depends on a number of factors and will be advised by doctor — try to have the same doctor manage warfarin dose if possible

  • Only adjust with medical consult or in line with management plan
  • Do not over-correct single borderline abnormal INR readings by changing warfarin dose. If 0.5 or less outside range — may need to keep previous dose and retest in 2-3 days 
  • If INR outside range — check for possible cause especially if usually stable — eg new medicines, illness, change in diet, recent binge-drinking, ran out of medicines or left behind when travelling
  • Record this and advise doctor when discussing warfarin dose
  • Medical consult if
    • INR low in high risk person, eg mechanical heart valve — may need low molecular weight heparin (LMWH) injection
    • Bleeding or embolic/thromboembolic complications — do not adjust
    • Having surgery within 5 days — may need to stop temporarily

Lifestyle advice

  • Take tablets at the same time every day — when convenient for person to remember
  • Make sure the tablets are always the same brand — same colour, same dose combination
  • Make sure all people treating you are aware you are on warfarin — avoid drug interactions
  • Contraception for women of childbearing age. If pregnant or wanting to be — specialist consult 
  • Alcohol — safer drinking
  • Some foods interact with warfarin. These can be safely eaten but try to have to same amount every day — avoid sudden changes in amounts of green vegetables and salad greens
  • Avoid contact sports, eg football, rugby
  • Avoid practices that break the skin — piercings, some traditional practices
  • Be aware of signs of bleeding — bleeding gums, bruising, pink urine, dark stools

Do — if bleeding or elevated INR 

Table 7.37 Management of bleeding or elevated INR

INR/bleeding Do

Not bleeding
(INR 4.5 or more)
  • Stop warfarin
  • Medical consult — may suggest vitamin K*
    • If given — measure INR in 6–12 hours
  • Measure INR every 24 hours
  • Consider causes of high INR
  • Resume warfarin therapy at a reduced rate once INR is less than 4.5

Bleeding
(any INR)
  • Urgent medical consult about
    • Sending to hospital
    • Best warfarin reversal therapy
  • Stop warfarin
  • Control bleeding — use compression if possible

*Injectable form of vitamin K can be taken orally

Supporting resources  

  • Warfarin adjustment example
  • Adjusting INR — Queensland guidelines
  • How to manage Warfarin therapy guide