Oral Anticoagulant

Question 1

What is the brand name for warfarin?

Answer 1

Coumadin and Marevan

Question 2

What type of drug is warfarin?

Answer 2

Oral anticoagulant

Question 3

How does warfarin work?

Answer 3

Inhbitor of vitamin K epoxide reductase
Vitamin K1 cant be turned back into vitamin K
Vitamin K dependent clotting factors cannot be made (2,7,9 and 10)

Question 4

What happens to the PTT on warfarin?

Answer 4

Increases

Question 5

What INR range do you aim for?

Answer 5

2-3 (usually 1 in normal patients)

Question 6

What are the common uses for warfarin?

Answer 6

1. Prophylaxis and treatment of VTE
2. Prophylaxis for stroke in AF or rheumatic heart disease
3. Prophylaxis for stroke in heart valve replacement

Question 7

Why is warfarin not used in arterial thrombosis?

Answer 7

e.g. MI and thrombotic stroke

These are driven by platelet aggregation not clotting factors and are therefore treated with aspirin and clopidogrel

Question 8

What are the contraindications of using warfarin?

Answer 8

Immediate risk of haemorrhage (trauma and surgery)
Pregnancy (teratogen)
Bleeding disorders (haemophilia and thrombocytopenia)
Peptic Ulceration

Question 9

When should you use warfarin with caution?

Answer 9

Liver disease (less able to metabolise the drug therefore over anticoagulation is a risk)

Question 10

What are some interactions with warfarin?

Answer 10

CYP450 inducers (increase clotting)
CYP450 inhibitors (increase bleeding)
Antibiotics (kill gut flora that synthesise vitamin k and increase risk of bleeding)
Vitamin K

Question 11

What are the common side effects of warfarin?

Answer 11

Haemorrhage 
Hypersensitivity (Mac pap rash)
Alopecia 
Diarrhoea 
Hepatic dysfunction

Question 12

How is warfarin eliminated?

Answer 12

Metabolised by CYP450 with variable half life

Question 13

How long does it take for warfarin to work?

Answer 13

Peak concentration within the blood is within an hour of dose but peak pharmacological effect occurs 2/7 later.
This is because warfarin inhibits only the formation of new clotting factors whose half lives are up to 72 hours and so it takes time to act.

Question 14

Why is warfarin often given with heparin?

Answer 14

Heparin works immediately whilst warfarin is taking time to work (withdrawn when INR is correct)

Question 15

How long is warfarin usually given for VTE prophylaxis and treatment?

Answer 15

A single episode of VTE is usually treated with 3-6 months

Lifelong may be needed for recurrent episodes or cardiac disease

Question 16

When is warfarin usually taken?

Answer 16

18:00

Question 17

How is warfarin monitored?

Answer 17

INR

Patients have a yellow book (anticoagulation book to record when tablets are taken and blood test results)