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

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

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

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)

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

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

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

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

Table 7.37 Management of bleeding or elevated INR

*Injectable form of vitamin K can be taken orally