Warfarin

Question 1

mechanism of warfarin ?

Answer 1

inhibits epoxide reductase which prevents the reduction of vitamin K to its active hydrochloroquine form
which is required for the carboxylation of clotting factors II, VII, IX, X and protein C

Question 2

what can potentiate warfarin ?

Answer 2

cranberry juice
liver disease
drugs which induce P450 enzyme:
- amiodarone
- ciprofloxacin 
antiplatelets i.e. NSAIDS
drugs which displace warfarin from albumin i.e. NSAIDS

Question 3

what are side effects of warfarin ?

Answer 3

haemorrhage
teratogenic
purple toes
skin necrosis (due to initial prothrombotic state due to inhibition of protein C = thrombus formation in venules)

Question 4

is safari safe to use during pregnancy and breastfeeding?

Answer 4

teratogenic but safe during breastfeeding

Question 5

what is the target INR when on warfarin ?

Answer 5

2.5

(with valve surgery INR is based individually. Mitral valve requires a higher INR)

(INR 3.5 is recurrent PE/DVT)

Question 6

how is INR calculated ?

Answer 6

patients prothrombin (PT) divided by normal PT

Question 7

management of a patient with major haemorrhage who is on warfarin ?

Answer 7

stop warfarin
IV 5mg vitamin K
prothrombin complex (FFP if unavailable)

continue warfarin when INR < 5

Question 8

management of a patient with an INR > 8 with minor bleeding?

Answer 8

stop warfarin
give IV 1-3mg vitamin K
repeat if still raised > 24 hours

continue warfarin when iNR < 5

Question 9

management of a patient with INR > 8 but no bleeding ?

Answer 9

stop warfarin
give oral 1-3mg vitamin K

continue warfarin when INR < 5

Question 10

management of a patient with INR 5-8 but no bleeding ?

Answer 10

withhold 1-2 doses of warfarin and reduce subsequent doses

Question 11

management of a patient with INR 5-8 with minor bleeding ?

Answer 11

stop warfarin
give IV 1-3mg vitamin K

continue warfarin when INR < 5