Warfarin

Question 1

How long does it take for warfarin’s anticoagulant effect to work

Answer 1

48 to 72 hours for the effect to fully develop

Question 2

What are the target INR for indications?

Answer 2

1. 1 or below in healthy people
2. 5 in most indications
3. 5 recurrent DVT or PE

Question 3

What is the duration of use of warfarin for isolated calf vein DVT and venous thromboembolism provoked by surgery and unprovoked proximal DVT or PE

Answer 3

Isolated calf- 6 weeks
Venous thromboembolism 3 months
unprovoked proximal DVT or PE: at least 3 months

Question 4

List the warning signs of that require immediate reporting to a doctor

Answer 4

• Haemorrhage- reversed with phytomenadione (nosebleeds, bleeding from wounds, bruising
• DVT/Pulmonary embolism (pain, swelling, tenderness in calf, skin redness, chest pain, SOB)
• Haemorrhagic stroke (headaches, confusion)
• Rash, skin necrosis, purple toes
• Diarrhoea and vomiting (poor absorption)

Question 5

What should you monitor for in warfarin

Answer 5

• INR: on alternate days in early treatment days, then at longer intervals of 12 weeks
• LIVER FUNCTION
• RENAL FUNCTION
• FBC
• BLOOD PRESSURE
• THYROID function

Question 6

What are the pregnancy implications of warfarin

Answer 6

Teratogenic- avoid in pregnancy especially in first or third trimesters- risk of congenital malformations, placental and foetal or neonatal haemorrhages

Question 7

What are the breast feeding implications of warfarin

Answer 7

Significant amounts of warfarin are not present in breast milk so should be safe

But increased risk of haemorrhage especially in vitamin K deficiency

Question 8

What are the common interactions with certain drugs and warfarin

Answer 8

Anticoagulant effects increased by:

• Enzyme Inhibitors like St Johns wort, clarithromycin, fluconazole, esomeprazole
• NSAIDs, clopidogrel, corticosteroids
• Cranberry juice

Anticoagulant effect reduced by:

• Enzyme inducers like carbmazepine, griseofulvin, mercaptopurine, phenobarbital
• VITAMIN K

Question 9

What are the implications in patients with hepatic impairment in using warfarin

Answer 9

Use with caution in mild to moderate impairment: avoid in severe impairment

Question 10

What are the implications in patients with renal impairment in using warfarin

Answer 10

Use with caution in mild to moderate impairment: in severe impairment monitor INR more frequently