Generic Name

Warfarin Sodium

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Classification

FDA Approved Indications

• Prevention and treatment of venous thromboembolism (deep vein thrombosis, pulmonary embolism)
• Atrial fibrillation with embolization risk
• Mechanical heart valve thromboembolism prevention

Mechanism of Action

Warfarin inhibits hepatic synthesis of vitamin K-dependent clotting factors II, VII, IX, and X, leading to anticoagulation.

Dosage and Administration

Adult: Initial dose usually 2-5 mg daily, adjusted based on INR; maintenance varies.

Pediatric: Use is limited; dosing individualized.

Geriatric: Start at lower doses due to increased bleeding risk; monitor closely.

Renal Impairment: Adjust dose based on INR; no specific dose reduction common.

Hepatic Impairment: Use with caution; start at lower doses; monitor INR closely.

Pharmacokinetics

Absorption: Well absorbed orally

Distribution: Widely distributed; crosses placenta and enters breast milk

Metabolism: Extensively metabolized in the liver via CYP2C9 and other isoenzymes

Excretion: Metabolites excreted in urine and feces

Half Life: Approximately 20-60 hours (variable)

Contraindications

• Recent or potential hemorrhagic tendencies
• Ongoing serious bleeding
• History of warfarin-induced skin necrosis

Precautions

• Use with caution in pregnancy (category X), bleeding disorders, uncontrolled hypertension, recent surgery, severe hepatic/renal impairment, alcohol use, elderly, frail patients

Adverse Reactions - Common

• Bleeding (Very common)
• Bruising (Common)
• Nausea or vomiting (Less common)

Adverse Reactions - Serious

• Hemorrhage (major bleed) (Serious and potentially life-threatening)
• Purple toe syndrome (Rare)
• Warfarin-induced skin necrosis (Rare)

Drug-Drug Interactions

• NSAIDs, antiplatelet agents, other anticoagulants, certain antibiotics (e.g., sulfamethoxazole, metronidazole), amiodarone, phenobarbital

Drug-Food Interactions

• High intake of vitamin K-rich foods (e.g., leafy greens) can reduce efficacy

Drug-Herb Interactions

• Ginseng, ginkgo, St. John’s Wort may affect anticoagulation

Nursing Implications

Patient/Family Teaching

• Take medication exactly as prescribed.
• Report any bleeding, bruising, or unusual symptoms.
• Maintain consistent intake of vitamin K-containing foods.
• Use soft toothbrush and electric razor to prevent bleeding.

Special Considerations

Black Box Warnings:

• Major or fatal bleeding may occur; use cautiously.

Genetic Factors: CYP2C9 and VKORC1 gene polymorphisms can affect dose requirements.

Lab Test Interference: Warfarin can interfere with some coagulation assays.

Overdose Management

Signs/Symptoms: Excessive bleeding, hematuria, gastrointestinal bleeding, intracranial hemorrhage

Treatment: Administer vitamin K (phytonadione) IV or oral; fresh frozen plasma or prothrombin complex concentrates in severe cases; discontinue warfarin.

Storage and Handling

Storage: Store at room temperature away from moisture and light.

Stability: Stable when stored properly; verify expiration date.