What CYP2C9 and VKORC1 variants reduce warfarin dose requirements?

CYP2C9*2, *3 reduce warfarin metabolism (require 15-50% dose reduction); VKORC1-1639A (low expression haplotype) reduces VKORC1, increasing warfarin sensitivity (30-50% dose reduction); Asian patients often need lower doses.

How should warfarin be adjusted for supratherapeutic INR without bleeding?

INR 3-5 (target 2-3): hold 1-2 doses, resume at 10-20% lower dose; INR 5-9: hold, consider 1-2.5 mg vitamin K1 PO if bleeding risk elevated; INR >9: hold, 2.5-5 mg vitamin K1 PO, recheck in 24h.

What is a good time in therapeutic range (TTR) target?

TTR ≥70% is a target for well-controlled warfarin; TTR <65% suggests poor control and consideration of DOAC if eligible; Rosendaal method calculates TTR from consecutive INR values over time.

Which drugs cause the most significant warfarin interactions?

Major potentiators: amiodarone, metronidazole, fluconazole, trimethoprim-sulfamethoxazole, clarithromycin; major inhibitors: rifampin, carbamazepine, nafcillin, chronic alcohol use; always check before adding any new medication.

What diet instructions should warfarin patients receive?

Consistent vitamin K intake (not elimination); dark green vegetables can be eaten regularly; sudden large changes in vitamin K intake affect INR more than steady consumption; alcohol in moderation.

Warfarin Dose Adjustment and INR Management Calculator

Guides warfarin dose adjustment based on current INR, target INR range, time in therapeutic range (TTR), and CYP2C9/VKORC1 pharmacogenomics to optimize anticoagulation with bleeding risk assessment.

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Frequently Asked Questions

What CYP2C9 and VKORC1 variants reduce warfarin dose requirements?

How should warfarin be adjusted for supratherapeutic INR without bleeding?

What is a good time in therapeutic range (TTR) target?

Which drugs cause the most significant warfarin interactions?

What diet instructions should warfarin patients receive?