Warfarin Flashcards
What is the main use for warfarin?
Used as an anticoagulant
Mechanism of action for warfarin?
Inhibits vitamin K
Factors II (prothrombin), VII, IX and X (+ protein C and protein S) require vitamin K for the final carboxylation step, this is essential for function.
Contraindications and cautions of warfarin?
Warfarin has a narrow therapeutic window - need to monitor therapy using INR.
What is INR?
The international normalised ratio (INR) blood test tells you how long it takes for your blood to clot.
It is used to test clotting times in people taking warfarin (a medicine used to treat and prevent blood clots).
INR result is used to work out what dose of warfarin you should take.
Adverse effects of warfarin?
Major adverse effect of warfarin is haemorrhage.
Bleeding complications
What are factors that may increase bleeding risk?
Intensity of anticoagulation
Associated clinical disorders
Associated use of other medications
Drug interactions
Quality of management
What are examples of mild bleeding complications?
Skin bruising
Epistaxis
Haematuria
What are examples of severe bleeding complications?
Gastrointestinal
Intracerebral
Significant drop in Hb
If reversal of warfarin complications required, what are the options?
Action is dependant on bleeding severity and INR
- No action
- Omit warfarin dose
- Administer oral vitamin K (works in 6 hours)
- Administer clotting factors (works immediately)
- Clinical and laboratory assessment of response
- Prothrombin complex concentrate (PCC): contains vitamin-K dependent clotting factors; PCC containing factors II, VII, IX and X is known as 4-factor PCC whilst PCC without factor VII is known as 3-factor PCC.
- If PCC unavailable, give fresh frozen plasma (FFP) which contains normal levels of all coagulation factors
Administration of warfarin?
PO (orally)
Dose should be taken at same time every day (6pm is recommended)
What is the INR?
The INR (international normalised ratio) is used to assess how anticoagulated the patient is by warfarin.
The INR calculates the patient’s prothrombin time compared with the prothrombin time of an average healthy adult.
How long can warfarin take to bring INR to therapeutic range?
Around 5 days
What is therapeutic range for INR for someone with AF?
Normal value = around 1.1
Therapeutic range for AF = 2-3
Slightly higher range for valve replacement and can vary depending on valve.
What are the various indications for warfarin?
Treatment of venous thromboembolism (deep vein thrombosis and pulmonary embolism)
Atrial fibrillation: if anticoagulation is indicated for prophylaxis of systemic embolisation
Rheumatic heart disease: for prophylaxis of systemic embolisation
Mechanical heart valves: for prophylaxis of systemic embolisation and valve thrombosis
Mitral valve disease, irrespective of valve replacement, for prophylaxis of systemic embolisation
Inherited, symptomatic thrombophilia
What are the various contraindications for warfarin?
Malignancy (heparin or a DOAC must be used in this instance)
Known hypersensitivity to warfarin or its ingredients
Haemorrhagic stroke
Clinically significant bleeding
Potential bleeding lesions (e.g. active peptic ulcer, oesophageal varices)
Uncorrected major bleeding diathesis (e.g. haemophilia, chronic kidney disease)
Pregnancy, due to the risk of congenital malformations and foetal death (breastfeeding is allowed)
Within 72 hours of major surgery with the risk of severe bleeding
Within 48 hours postpartum
Uncontrolled severe hypertension
Patient factors (e.g. uncooperative, unreliable and/or high risk of repeated falls)
Drugs with which there is a significantly increased risk of bleeding (e.g. antiplatelet drugs, non-steroidal anti-inflammatory drugs, and enzyme inhibitors)
