Warfarin Dose Adjustment
Enter the current INR, indication, and weekly dose to receive a suggested percentage adjustment and monitoring plan. Always confirm with institutional protocols.
Typical maintenance goal INR 2.0–3.0.
Sum of all daily doses over 7 days.
Dose Adjustment Recommendation
Adjustment
0%
Current weekly dose 35.0 mg → New target 35.0 mg/week.
Monitoring plan
Recheck INR in 7 day(s) or sooner if symptoms arise.
Suggested next steps
INR at goal. Continue current weekly dose and recheck within recommended interval (4 weeks if stable).
How to Use This Calculator
Collect accurate dosing history
Verify the total weekly warfarin dose and adherence before adjusting.
Enter the current INR and indication
The tool selects the typical therapeutic range or lets you define a custom goal.
Apply recommendations with clinical judgement
Confirm adjustments with pharmacists or anticoagulation clinic protocols and schedule appropriate follow-up.
Formula
Adjusted weekly dose = Current weekly dose × (1 + recommended % change).
Derived from ACCP Antithrombotic Therapy Guidelines (CHEST) and anticoagulation clinic dosing algorithms.
About Warfarin Dose Management
Warfarin has a narrow therapeutic index and numerous drug–food interactions. Dose adjustments are typically made on a weekly basis using percentage changes informed by the current INR relative to the therapeutic range. Minor deviations within ±0.5 of the goal often require small (5–10%) adjustments, whereas larger excursions necessitate holding doses, administering vitamin K, and closer follow-up. Always assess adherence, diet (vitamin K intake), and interacting medications (e.g., antibiotics, amiodarone) before changing the dose.
Patients with mechanical heart valves or recent thromboembolism have higher target ranges and may require bridging with parenteral anticoagulants if the INR is severely subtherapeutic. Educate patients about maintaining consistent vitamin K intake, avoiding binge alcohol consumption, and promptly reporting signs of bleeding or thrombosis.
Frequently Asked Questions
When should I bridge with LMWH or heparin?
Consider bridging for mechanical valves, recent VTE (<3 months), or high-risk patients when INR <1.5. Consult anticoagulation specialists.
How soon should INR be rechecked after a large adjustment?
Within 3–5 days for significant subtherapeutic or supratherapeutic INRs, sooner if symptoms occur.
What factors can suddenly increase INR?
Antibiotics (TMP-SMX, macrolides), amiodarone, acute illness, poor oral intake, alcohol binges, and hepatic dysfunction all increase INR.
How should I document the dosing plan?
List the daily dosing schedule explicitly (e.g., 5 mg daily except 7.5 mg on Monday) and record follow-up date and patient counseling.
What if the patient missed doses?
Assess adherence. A missed dose can explain subtherapeutic INR; correct adherence before major dose increases.