Warfarin Dosing Calculator
Calculate Coumadin dose adjustments based on INR levels and target ranges
Warfarin Dose Adjustment Calculator
FOR HEALTHCARE PROFESSIONALS ONLY
Warfarin dosing requires careful monitoring. Bleeding risk increases with high INR. Always follow ACCP/ASH guidelines and institutional protocols.
Latest INR measurement from blood test
Therapeutic target range for condition
Some patients don't take warfarin every day
Bleeding status affects dosing recommendations
Clinical Example
Case: Atrial Fibrillation Patient
Patient: 65-year-old with atrial fibrillation
Target INR: 2.0-3.0
Current dose: 35 mg/week (5 mg daily)
Current INR: 4.2
Recommendation
Action: Hold warfarin or decrease dose by 5-20%
New weekly dose: 28-31.5 mg/week
Follow-up: INR check in 1 day
Monitor: Signs of bleeding, patient compliance
INR Target Ranges
INR 2.0-3.0
- • Atrial fibrillation
- • Deep vein thrombosis
- • Pulmonary embolism
- • Cardiomyopathy
- • Stroke prevention
INR 2.5-3.5
- • Mechanical heart valves
- • High-risk thrombosis
- • Recurrent VTE on warfarin
Bleeding Risk Factors
- • Age >75 years
- • History of bleeding
- • High INR (>4.0)
- • Comorbid conditions
- • Drug interactions
- • Poor anticoagulation control
- • Excessive alcohol use
Factors Affecting INR
Increase INR:
- • Antibiotics (metronidazole)
- • Decreased vitamin K intake
- • Liver disease
- • Illness with poor oral intake
- • Drug interactions
Decrease INR:
- • Increased vitamin K intake
- • Non-compliance
- • Drug interactions
- • Malabsorption
- • Enzyme inducers
Understanding Warfarin Dosing and INR Management
What is Warfarin?
Warfarin (Coumadin) is an oral anticoagulant that prevents blood clot formation by inhibiting vitamin K-dependent clotting factors (II, VII, IX, X). It's commonly used for stroke prevention in atrial fibrillation and treatment of venous thromboembolism.
Why Monitor INR?
- •INR measures anticoagulation effect
- •Prevents both clotting and bleeding
- •Guides safe and effective dosing
- •Detects drug/food interactions
Dosing Principles
Warfarin dosing follows evidence-based guidelines from ACCP and ASH:
- •Small dose adjustments (5-20%)
- •Weekly dose calculations
- •Frequent INR monitoring
- •Patient education and compliance
Important: Always consider patient-specific factors including age, comorbidities, drug interactions, and bleeding risk.
INR Adjustment Guidelines
| INR Range (2-3) | INR Range (2.5-3.5) | Recommended Action |
|---|---|---|
| <1.5 | <2.0 | Increase dose 5-20%, consider booster |
| 1.5-1.9 | 2.0-2.4 | Increase dose 5-15%, consider booster |
| 2.0-3.0 | 2.5-3.5 | Therapeutic range - no change |
| 3.1-3.2 | 3.6-3.7 | Consider omitting dose or decrease 5-10% |
| 3.5-3.9 | 4.0-4.4 | Omit dose or decrease 5-15% |
| >4.0 | >4.5 | Hold warfarin, decrease dose 5-20% |
⚠️ CRITICAL ANTICOAGULATION DISCLAIMER
FOR HEALTHCARE PROFESSIONALS ONLY. Warfarin is a high-risk medication requiring careful monitoring and dosing. This calculator provides guidance based on established guidelines but cannot replace clinical judgment.
BLEEDING RISK: Warfarin can cause serious or fatal bleeding. Always assess bleeding risk, drug interactions, patient compliance, and individual factors before making dosing decisions.
Healthcare providers must verify all calculations independently and follow institutional protocols. Always consult ACCP/ASH guidelines and consider hematology consultation for complex cases or bleeding events.
EMERGENCY SITUATIONS: For serious bleeding or supratherapeutic INR with bleeding, immediately discontinue warfarin and consider reversal agents (vitamin K, PCC, FFP).