Warfarin (Coumadin)
Vitamin K antagonist oral anticoagulant; racemic mixture of (R)- and (S)-enantiomers where (S)-warfarin is 3-5x more potent. Competitively inhibits VKORC1, reducing synthesis of active clotting factors (II, VII, IX, X). Rapidly absorbed (tmax ~4h), highly protein-bound (~99%), metabolized primarily by CYP2C9 with genetic polymorphisms causing dose variability. Narrow therapeutic window (INR 2-3); requires frequent monitoring. Long onset (24-72h) and offset (2-5 days). Extensive drug interactions with NSAIDs, SSRIs, antibiotics, statins, and other CYP450 substrates. Genetic testing (CYP2C9, VKORC1) increasingly recommended for dosing.
Projected serum levels — 5 mg, once daily
Maintenance schedule: 5 mg once daily (oral).
Loading schedule: 13.0 mg on day 1, then 5 mg once daily — reaching therapeutic levels sooner.
Modeled steady state after ~4 days: peak ≈ 12.0 mg, trough ≈ 7.9 mg body load. Population-based estimate over 15 days for a 5 mg dose at a 70 kg reference body mass — the interactive app scales curves to your doses, timing, and body mass.
Key facts
- Category
- Anticoagulant
- Route modeled
- Oral
- Model confidence
- inferred
- Half-life
- 36 h
- Common dose
- 5 mg
- Suggested maximum
- 15 mg/day
- Reference dose range
- 1–15 mg (single dose)
- Suggested cadence
- once daily
- Validated against
- 10 mg oral — Cmax 1.5 mg/L at 4 h
Documented interactions
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danger
Apigenin + Warfarin (Coumadin)
Apigenin may displace Warfarin (Coumadin) from plasma protein binding sites, transiently raising free drug concentration. This drug has a narrow therapeutic index; free concentration changes can…
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danger
Aripiprazole (Abilify) + Warfarin (Coumadin)
Aripiprazole (Abilify) may displace Warfarin (Coumadin) from plasma protein binding sites, transiently raising free drug concentration. This drug has a narrow therapeutic index; free concentration…
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danger
Astaxanthin + Warfarin (Coumadin)
Astaxanthin may displace Warfarin (Coumadin) from plasma protein binding sites, transiently raising free drug concentration. This drug has a narrow therapeutic index; free concentration changes can…
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danger
Atomoxetine (Strattera) + Warfarin (Coumadin)
Atomoxetine (Strattera) may displace Warfarin (Coumadin) from plasma protein binding sites, transiently raising free drug concentration. This drug has a narrow therapeutic index; free concentration…
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danger
Atorvastatin (Lipitor) + Warfarin (Coumadin)
Atorvastatin (Lipitor) may displace Warfarin (Coumadin) from plasma protein binding sites, transiently raising free drug concentration. This drug has a narrow therapeutic index; free concentration…
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danger
Black Seed Oil (Nigella sativa / Thymoquinone) + Warfarin (Coumadin)
Black Seed Oil (Nigella sativa / Thymoquinone) may displace Warfarin (Coumadin) from plasma protein binding sites, transiently raising free drug concentration. This drug has a narrow therapeutic…
Serum checks 178 modeled interaction pairings for warfarin (coumadin) across your whole stack — absorption conflicts, enzyme inhibition, and nutrient depletion included.
Research behind this entry
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Comparative pharmacokinetics of vitamin K antagonists: warfarin, phenprocoumon and acenocoumarol
Comparative PK study showing warfarin has shortest half-life (40h) among vitamin K antagonists and highest variability in dose-response due to CYP2C9/VKORC1 polymorphisms.
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American Heart Association/American College of Cardiology Foundation Guide to Warfarin Therapy
Comprehensive clinical guideline establishing warfarin dosing strategies, monitoring requirements, INR targets by indication, and management of drug interactions and bleeding.
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Warfarin and vitamin K intake in the era of pharmacogenetics
Meta-analysis demonstrating CYP2C9 and VKORC1 genetic variation explains ~50% of warfarin dose variability and pharmacogenetic testing can improve dosing accuracy.
3 published studies referenced in the app, each with a plain-language summary.