Warfarin Dosing and Management

Dose Adjustment by INR

• <1.5: Increase weekly dose by 20%

• 1.5–1.9: Increase weekly dose by 10%; repeat INR in 1 week

• >3: Decrease dose or omit next dose based on elevation and clinical context

Screening Questions

• Changes in diet (e.g., green leafy vegetables affecting vitamin K)

• New medications (e.g., antibiotics, NSAIDs, SSRIs)

• Recent illnesses (e.g., liver disease, thyroid dysfunction)

Factors Affecting INR

Increase INR:

• Reduced vitamin K intake, liver disease, hyperthyroidism, heart failure, infections

• Drugs: Doxycycline, omeprazole

Decrease INR:

• Increased vitamin K intake, hypothyroidism

• Drugs: Antihistamines, penicillins

When to Suggest Vitamin K

• INR >10 (no bleeding): 1–5 mg orally

• INR 4.5–10 + High Bleeding Risk: 1–2 mg orally or IV, recheck in 24 hrs

• Active Bleeding (any INR): Immediate reversal with IV vitamin K + prothrombin complex concentrate (PCC)

Indications for Warfarin Therapy

• Stroke Prevention: AF with CHADS2 score ≥2

• Venous Thromboembolism: Treatment and secondary prevention

• Prosthetic Heart Valves: Mechanical valves or rheumatic mitral stenosis

• Post-MI Thromboembolism Prophylaxis: Mural thrombus, LV dysfunction

CHADS2 Scoring to decide warfarinisation in AF

• CHF (1), Hypertension (1), Age ≥75 (1), Diabetes (1), Stroke/TIA (2)

• Score 0: No anticoagulation or aspirin

• Score 1: Consider aspirin or warfarin

• Score ≥2: Warfarin strongly indicated

Contraindications

Absolute

• Active bleeding or recent major haemorrhage

• Severe bleeding disorders (e.g., haemophilia)

• Severe liver disease, platelets <50 x 10⁹/L

• Pregnancy

Relative

• High falls risk

• Poor adherence or limited INR access

• Severe uncontrolled hypertension

Additional Notes

• Educate patients on recognising bleeding, dietary consistency, and monitoring adherence

• Regular INR monitoring is critical to optimise therapy and minimise bleeding risk