Novel anticoagulants (warfarin)

Question 1

Indications

Answer 1

1. To prevent clot extension and recurrence in DVT and PE (VTE)
2. To prevent embolic complications of AF
3. To prevent embolic complications for heart valve replacement

Only to prevent venous thrombosis (arterial driven by platelets)

Question 2

Mechanism of action

Answer 2

Inhibits hepatic production of Vit K-dependent clotting factors.

Inhibits vitamin K epoxide reductase

Question 3

Adverse effect

Answer 3

Bleeding

Question 4

Warnings

Answer 4

Low therapeutic index

Question 5

Interactions

Answer 5

Cytochrome P450 oxidase inhibitors (macrolides etc) decrease warfarin metabolism and increase bleeding risk.

Cytochrome P450 inducers (phenytoin, carbamazepine etc) increase warfarin metabolism.

Many abx increase anti-coagulation in patients on warfarin by killing gut flora which synthesise Vit K.

Question 6

Prescribing

Answer 6

PO once daily

Dose guided by INR

Question 7

Administration

Answer 7

Usually taken each day at 18:00

Question 8

Communication

Answer 8

Advise patients that warfarin treatment is a balance between benefits and risks

Question 9

Monitoring

Answer 9

INR