Warfarin

Question 1

What is it?

Bleeding time

Answer 1

Warfarin is an oral anticoagulant which inhibits epoxide reductase preventing the reduction of vitamin K to its active hydroquinone form, which in turn acts as a cofactor in the carboxylation of clotting factor II, VII, IX and X (mnemonic = 1972) and protein C

Affects Prothrombin Time

Question 2

Indications and target INR

Answer 2

Venous thromboembolism: target INR = 2.5, if recurrent 3.5

Atrial fibrillation, target INR = 2.5

Mechanical heart valves = target INR depends on the valve type and location
= Mitral valves generally require a higher INR than aortic valves.

Question 3

Management of high INR

Answer 3

INR 5-8 no bleeding: withold 1-2 doses, then restart

INR 5-8 minor bleeding: withold doses, give 1 - 3mg Vitamin K IV, restart when INR < 5

INR over 8 no bleeding: withold doses, give 1 - 5 mg Vitamin K orally (use the IV med), restart when INR <5

INR over 8 minor bleeding: withold doses, give Vitamin K IV, if still high after 24 hours repeat dose, restart when INR < 5

INR over 8 major bleeding: withold doses, give prothrombin complex (or FFP if not available)

Vitamin K = phytomenadione