Warfarin Flashcards
What class of medication is warfarin?
Vitamin K antagonist
What is the mechanism of action of warfarin?
Prevents the formation of clotting factors 2, 7, 9, and 10, by competitive inhibition of the vitamin K epoxide reductase enzyme
What are the clinical indications for warfarin?
Prophylaxis of embolization in rheumatic heart disease and AF
Prophylaxis after insertion of prosthetic heart valve
Prophylaxis of VTE and PE
TIA
What is the typical dose of warfarin?
Loading dose 5-10mg OD, by mouth
Maintenance dose 3-9mg, at the same time each day
What are the common adverse effects of warfarin?
Haemorrhage
Bruising
What are the important side effects of warfarin?
Hypersensitivity
Skin necrosis
Liver dysfunction
Jaundice
Pyrexia
What are the contraindications to warfarin?
Pregnancy - first trimester
48 hours postpartum
Haemorrhagic stroke
Significant bleeding
What are the cautions for warfarin?
Recent surgery
Recent ischaemic stroke
Uncontrolled hypertension
Bacterial endocarditis
History of GI bleed
Peptic ulcer
How is warfarin monitored?
Baseline INR should be determined
INR should be taken daily or every other day initially until stabilised
INR should then be monitored up to every 12 weeks
What information should be communicated to patients taking warfarin?
Do not take with any OTC medications without checking with a pharmacist
Inform anyone that starts you on a new medication that you are taking warfarin
Use reliable contraception while on warfarin, if a woman of child bearing age
Avoid drinking cranberry juice, and avoid major changes to diet
Avoid excessive alcohol consumption whilst on warfarin
Take warfarin at the same time every day
How is major bleeding whilst on warfarin managed?
Stop warfarin
Give IV vitamin K 5mg
Give prothrombin complex concentrate
How is INR > 8 with minor bleeding managed?
Stop warfarin
Give IV vitamin K 1-3mg
Repeat dose of vitamin K if INR is still high after 24 hours
Restart warfarin when INR < 5
How is INR > 8 with no bleeding managed?
Stop warfarin
Give IV vitamin K 1-5mg
Restart warfarin when INR <5
How is INR 5-8 with minor bleeding managed?
Stop warfarin
Give IV vitamin K 1-3mg
Restart when INR <5
How is INR 5-8 with no bleeding managed?
Withold 1 or 2 doses of warfarin
Reduce subsequent maintenance dose
