DRUG OF THE DAY
warfarin
Vitamin K antagonist anticoagulant
Before opening the card, recall one use, one safety check and one counseling point.
Reveal the drug learning card
Names and formulations
- Jantoven: oral tablet
Tablet strengths are color coded, but strength should always be verified from the label; dosing is individualized to INR and clinical context.
Common use
Prevention and treatment of venous thromboembolism and thromboembolic complications associated with atrial fibrillation or cardiac valve replacement.
Mechanism of action
Inhibits vitamin K epoxide reductase, reducing synthesis of active vitamin K-dependent clotting factors II, VII, IX, and X and proteins C and S.
Important adverse effects and monitoring
- Boxed warning: can cause major or fatal bleeding; regular INR monitoring is required.
- Monitor for bleeding, interacting drugs, illness, alcohol changes, and major dietary changes; rare serious harms include skin necrosis and calciphylaxis.
- Generally contraindicated in pregnancy, with a narrow exception framework for selected patients with mechanical valves.
Patient counseling
- Keep vitamin K intake reasonably consistent rather than eliminating vitamin K-containing foods.
- Check before starting or stopping prescriptions, over-the-counter medicines, herbals, or supplements.
Interaction to recognize
With: trimethoprim-sulfamethoxazole and many other antimicrobials
Why it matters: May increase anticoagulant effect and bleeding risk.
Practical response: Coordinate closer INR monitoring and warfarin dose management when a clinically important interacting drug is started or stopped.
Check the original sources
- DailyMed — Jantoven (warfarin) prescribing information
Sections: Boxed Warning; 1 Indications and Usage; 2.1 Individualized Dosing; 5 Warnings and Precautions; 7 Drug Interactions; 12.1 Mechanism of Action; 17 Patient Counseling Information. Source checked 2026-09-13.
Selected learning points; verify current labeling for the complete prescribing information.