Warfarin Dose Adjustment for INR 3.4
Withhold warfarin for 1 dose, then restart at 4 mg daily (20% dose reduction from the current 5 mg), and recheck INR in 3-5 days. 1, 2
Immediate Management
Stop warfarin immediately until the INR falls below 3.5, as the current INR of 3.4 is above your goal range of 2-2.5 and increases bleeding risk 1, 2
Do not administer vitamin K at this INR level—vitamin K is reserved for INR >4.5-5.0 without bleeding, or lower levels with active bleeding 1
The American College of Chest Physicians guidelines specifically recommend that when INR is above therapeutic range but <5, and the patient has no clinically significant bleeding, simply reduce or omit the next dose and resume at a lower dose when INR approaches the desired range 1
Dose Adjustment Algorithm
Reduce the weekly warfarin dose by 20%: From 5 mg daily (35 mg/week) to 4 mg daily (28 mg/week) 2
The American Society of Hematology/International Society on Thrombosis and Haemostasis specifically recommends restarting at 80% of the previous dose (20% reduction) when INR exceeds 3.5 2
This 1 mg/day reduction is clinically significant—studies demonstrate that even a 1 mg/day difference in warfarin dosing substantially affects bleeding risk when targeting INR ranges 1
Monitoring Protocol
Recheck INR in 3-5 days after restarting warfarin at the reduced dose 2
Continue monitoring every 3-7 days until INR stabilizes within the 2-2.5 range 1
Once stable in therapeutic range for 2 consecutive measurements, monitoring frequency can be gradually extended to weekly, then up to every 4 weeks 1
Why This Approach
INR 3.4 carries increased bleeding risk: The risk of major bleeding increases exponentially above INR 3.0, with intracranial hemorrhage risk particularly elevated above 3.5 1
Your goal INR of 2-2.5 is lower than standard: Most guidelines target 2.0-3.0 (aiming for 2.5), but your narrower range of 2-2.5 suggests either increased bleeding risk factors or specific clinical circumstances requiring tighter control 1
Vitamin K would overshoot: At INR 3.4, vitamin K administration would likely drop the INR below therapeutic range and create a period of inadequate anticoagulation, plus cause warfarin resistance for several days 1
Common Pitfalls to Avoid
Do not restart at the same 5 mg dose—this will result in recurrent supratherapeutic INR within days 2
Do not give vitamin K intravenously unless life-threatening bleeding occurs, as anaphylactic reactions occur in 3 per 100,000 IV doses 2
Do not make dose adjustments based on a single INR once stable—but at 3.4 with goal 2-2.5, action is warranted 3
Avoid loading doses or large dose changes—most adjustments should alter weekly dose by 5-20%, and the 20% reduction here is appropriate 3
Risk Factors Requiring Extra Vigilance
Age >65 years, history of prior bleeding (especially gastrointestinal or intracranial), renal insufficiency, anemia, concomitant antiplatelet agents, or mechanical heart valves all increase bleeding risk at this INR level 1, 2
If any of these factors are present, consider holding warfarin for 2 doses instead of 1 before restarting at 4 mg daily 1