Oral anticoagulants

Question 1

What is an example

Answer 1

Warfarin

Question 2

What is the indication for use

Answer 2

• DVT + PE (collectively VTE) - prevent clot extension + recurrence
• Prevent embolic complications in AF
• Prevent embolic compl after heart valave replacement (life long if mechanical + not tissue)

Question 3

Why is warfarin not used for arterial thrombosis

Answer 3

e.g. MI, thrombotic stroke

Bc this is driven by platelet aggregation (use aspirin + clopidogrel)

Question 4

What is the mechanism of action

Answer 4

• Inhibits hepatic production vitamin K-dependent coagulation factors + cofactors
• inhibits Vit K epoxide reductase –> prevents reactivation Vit K + coagulation factor synthesis

Question 5

What are the side effects

Answer 5

• Bleeding

Question 6

What are the contra-indications

Answer 6

• Narrow therapeutic index
• Immediate risk haemorrhage (trauma + surgery pt)
• Liver disease (less able to metabolise drug)
• pregnancy (1st trimester + near term - may cause maternal haemorrhage at birth)

Question 7

What are the interactions

Answer 7

• Cytochrome P450 inhibitors e.g. fluconazole, macrolides) decrease warfarin metabolism + ^ risk bleed
• Cytochrome P450 inducers (e.g. carbamazepine, phenytoin, rifampicin) increase warfarin meta + 6 risk clots