Warfarin: clinical use

Prescribing considerations

• Confirm the continuing indication and individual bleeding risk.
• Review comorbidities, adherence, diet, alcohol, acute illness and all prescribed, non-prescription and complementary medicines.
• Use particular caution with severe hypertension, hepatic or renal disease, previous gastrointestinal bleeding, recent ischaemic stroke, falls risk, anaemia, malignancy and haemostasis-altering medicines.
• Closely monitor INR after switching warfarin preparations.

Contraindications and cautions

• Hypersensitivity to warfarin or product excipients.
• Haemorrhagic stroke or clinically significant active bleeding.
• Recent surgery carrying severe bleeding risk and the immediate postpartum period specified by the product information.
• Any condition where haemorrhage risk outweighs potential benefit.
• Concomitant treatment producing an unacceptably high bleeding risk, including fibrinolytics.
• Pregnancy contraindications differ between the selected tablet and suspension; consult the exact product information and obtain specialist input.

Monitoring

• Obtain baseline coagulation assessment and liver function information where indicated by the product information.
• Monitor INR regularly and increase surveillance during unstable control, acute illness, adherence problems, major dietary change or interacting treatment changes.
• Investigate unexpected INR results for administration errors, interactions or changes in diet, alcohol, smoking, weight or health.
• Monitor for bleeding, anaemia, painful skin lesions and anticoagulant-related nephropathy.

Clinical pharmacology

Warfarin is a racemic coumarin anticoagulant. S-warfarin is mainly metabolised through CYP2C9 and R-warfarin through CYP1A2 and CYP3A4. It is highly protein-bound, has a plasma half-life of about 40 hours and reduces synthesis of vitamin K-dependent clotting factors.

Formulation and product differences

• The selected uncoated tablet contains lactose, is essentially sodium-free and has a score line not intended for splitting.
• The selected oral suspension contains liquid maltitol, propylene glycol and benzoic acid and is essentially sodium-free. Its excipients need additional consideration in fructose intolerance, hepatic or renal disease, pregnancy, breastfeeding and neonates.
• The selected oral suspension is licensed for adults and its product information does not recommend paediatric use.

Oral suspension

Route: Oral

Strengths: 1 mg/1 mL

Tablet

Route: Oral

Strengths: 0.5 mg, 5 mg