Warfarin Dosing
Induction & Maintenance Calculator
⚠️ Clinical Safety Warning: Warfarin has a narrow therapeutic index. This tool provides guidance based on standard protocols (Coventry/BSH). Individual patient factors (bleed risk, interacting meds like Amiodarone/Antibiotics) must be considered. Always follow your local anticoagulation policy.
Initiation Phase
Dosing Protocols
Loading (Rapid Induction)
Based on the modified Fennerty/Oates protocol. Standard start is 10mg Day 1, 10mg Day 2 (unless INR rises rapidly). Reduce starting dose to 5mg for elderly (>75), low weight, or high bleeding risk.
Maintenance Adjustment
Adjustments are typically made by calculating the Total Weekly Dose (TWD).
- INR Low: Increase TWD by 5-20%.
- INR High (3.0-4.5): Decrease TWD by 5-10%.
- INR > 5.0: Omit doses and recheck.
- INR > 8.0: Stop, check for bleeding, consider Vitamin K (1-5mg oral).