WARFARIN

Question 1

Warfarin - what type of medication is this?

Answer 1

Anticoagulant

Question 2

Warfarin - indications

Answer 2

Treatment and prevention of recurrence of Venous thromboembolism (VTE)
Initial concomitant (alongside, combined) therapy of warfarin with heparin required; alternatively DOACs can be used 

To prevent arterial embolism in patients with atrial fibrillation (AF) or prosthetic heart valves
For non-valvular AF, DOACs are alternatives
For prosthetic heart valves, treatment is short term (after tissue valve replacement) and life-long (after mechanical valve replacement)

Question 3

Warfarin - what is the alterative to warfarin in patients with non-valvular AF?

REMEMBER:
valvular AF = warfarin
(v next to w in alphabet)

Answer 3

DOACs

Question 4

Warfarin - administration

Answer 4

Taken each day at same time (6pm)

Question 5

Warfarin - MOA

Answer 5

1) inhibits vitamin K epoxide reductase
2) this inhibits hepatic production of vitamin K dependent coagulation factors (factors II, VII, IX and X and proteins C and S)
3) this makes your blood clot more slowly

remember
WaVER - warfarin inhibits vit k epoxide reductase

Question 6

Warfarin - adverse effects

Answer 6

→ The main adverse effect of Warfarin is bleeding

→ Minor over use can increase the risk of bleeding from a minor trauma (e.g.- minor head injury) and in existing abnormalities (e.g.- peptic ulcers)

→ Severe over use can trigger spontaneous bleeding such as epistaxis or retroperitoneal haemorrhage

Question 7

Warfarin - how can the adverse effects of warfarin reversed?

Answer 7

Adverse effect of warfarin can be reversed with phytomenadione (Vitamin K1) or dried prothrombin complex

Question 8

Warfarin - contraindications (avoid entirely)

Answer 8

AVOID:
→ In patients at immediate risk of haemorrhage (including after trauma and in patients requiring surgery)
→ In first trimester of pregnancy
Why? Risk of teratogenicity (cardiac and cranial abnormalities)
→ Later in pregnancy
Why? Risk of peripartum haemorrhage

Question 9

Warfarin - caution

Answer 9

CAUTION:
→ In patients with liver disease
Why? Less able to metabolise drug = increase risk of side effect

Question 10

Warfarin - interaction

Answer 10

CAUTION with:
→ Cytochrome P450 (CYP) inhibitors 
Why? Decreases warfarin metabolism and increases bleeding risk 
Examples:
Fluconazole 
Macrolides 

→ CYP inducers 
Why? Increases warfarin metabolism and risk of clots 
Examples:
Phenytoin 
Carbamazepine 
Rifampicin