Warfarin (or) Coumadin

Warfarin has a long half-life (i.e. 40 hours) therefore higher loading doses are required if a pharmacological effect is required quickly.

Phytomenadione (Vitamin K) and Menadiol Sodium phosphate (water soluble synthetic Vitamin K derivate) antagonises the effects of warfarin.

Indications:

• (bioprosthetic) valve > no need for warfarin > long term aspirin
• (bioprosthetic) valve + DVT > if given warfarin (here would be second line after DOAC) > INR 2.5
• DVT recurrence or DVT while on warfarin > INR 3.5
• Metallic aortic valve > warfarin INR 3.0

Contraindications

• Hypersensitivity
• Haemorrhagic stroke
• Clinically significant bleeding
• Pregnancy ( especially during the first and third trimester)
• Severe liver disease
• Severe renal impairment
• Within 72 hours of major surgery with severe risk of bleeding
• Within 48 hours postpartum

Warfarin is administered orally and metabolised in the liver by Cytochrome P450 enzymes.

Increased INR