VitalsCentral

Warfarin

Coumadin | Jantoven

FDA ApprovedCardiovascular AgentsAnticoagulants
Half-life: Approximately 20-60 hoursPregnancy: Category X

Overview

Warfarin is an oral vitamin K antagonist anticoagulant used to prevent and treat thromboembolic disorders such as venous thromboembolism and stroke in atrial fibrillation.

Indications

  • Venous thromboembolism treatment and prophylaxis
  • Atrial fibrillation
  • Mechanical heart valves
  • Prevention of recurrent thromboembolism

Contraindications

  • Active bleeding
  • Pregnancy
  • Severe hepatic disease
  • Recent or planned major surgery with high bleeding risk

Classification

Cardiovascular AgentsAnticoagulantsCardiovascular System

Mechanism of Action

Inhibits vitamin K epoxide reductase, reducing the regeneration of vitamin K and impairing gamma-carboxylation of clotting factors II, VII, IX, and X and proteins C and S.

Pharmacodynamics

Produces a delayed, dose-dependent anticoagulant effect monitored by the international normalized ratio (INR). Full effect takes several days as existing clotting factors are cleared.

Pharmacokinetics

Absorption
Rapidly and completely absorbed orally.
Distribution
Highly protein bound; small volume of distribution.
Metabolism
Metabolized by hepatic CYP2C9 (S-warfarin) and CYP1A2 and CYP3A4 (R-warfarin).
Excretion
Metabolites excreted in urine and bile.
Half-life
Approximately 20-60 hours
Bioavailability
Essentially complete
Protein Binding
Approximately 99%

Dosage

Typical dosage: Individualized to a target INR, commonly 2-10 mg once daily

Available Forms

  • Tablet
  • Injection

Side Effects

Common

  • Bruising
  • Minor bleeding
  • Nausea

Serious

  • Major hemorrhage
  • Intracranial bleeding

Rare

  • Skin necrosis
  • Purple toe syndrome

Drug Interactions

Aspirinmajor

Additive bleeding risk through combined anticoagulant and antiplatelet effects.

Amiodaronemajor

Inhibits warfarin metabolism, raising INR and bleeding risk; the warfarin dose usually must be reduced.

Warnings

⚠️BLACK BOX WARNING

Warfarin can cause major or fatal bleeding. Regular monitoring of INR is essential. Patients at high risk of bleeding should be evaluated carefully, and the drug requires careful dose management.

Pregnancy

Category X

Toxicity

Overdose manifests as bleeding, hematuria, and bruising.

Overdose

Manage with vitamin K (phytonadione); use prothrombin complex concentrate or fresh frozen plasma for serious bleeding.

References

Looking for patient-friendly information? Visit RemedyDoor for easy-to-read guides about this medication.