How long does it take for warfarin’s anticoagulant effect to work
48 to 72 hours for the effect to fully develop
What are the target INR for indications?
- 1 or below in healthy people
- 5 in most indications
- 5 recurrent DVT or PE
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
Isolated calf- 6 weeks
Venous thromboembolism 3 months
unprovoked proximal DVT or PE: at least 3 months
List the warning signs of that require immediate reporting to a doctor
- 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)
What should you monitor for in warfarin
- INR: on alternate days in early treatment days, then at longer intervals of 12 weeks
- LIVER FUNCTION
- RENAL FUNCTION
- FBC
- BLOOD PRESSURE
- THYROID function
What are the pregnancy implications of warfarin
Teratogenic- avoid in pregnancy especially in first or third trimesters- risk of congenital malformations, placental and foetal or neonatal haemorrhages
What are the breast feeding implications of warfarin
Significant amounts of warfarin are not present in breast milk so should be safe
But increased risk of haemorrhage especially in vitamin K deficiency
What are the common interactions with certain drugs and warfarin
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
What are the implications in patients with hepatic impairment in using warfarin
Use with caution in mild to moderate impairment: avoid in severe impairment
What are the implications in patients with renal impairment in using warfarin
Use with caution in mild to moderate impairment: in severe impairment monitor INR more frequently
