Home Drug Guide Warfarin Potassium

Drug Guide

Generic Name

Warfarin Potassium

Brand Names Athrombin-k

Classification

Therapeutic: Anticoagulant

Pharmacological: Vitamin K Antagonist

FDA Approved Indications

Prevention and treatment of venous thromboembolism (deep vein thrombosis, pulmonary embolism)
Prevention of stroke and systemic embolism in patients with atrial fibrillation

Mechanism of Action

Warfarin inhibits vitamin K epoxide reductase, leading to decreased synthesis of vitamin K-dependent clotting factors II, VII, IX, and X, thus impairing blood coagulation.

Dosage and Administration

Adult: Dosage varies based on indication; typically, initial dose is 2-5 mg once daily, adjusted based on INR.

Pediatric: Use is limited; dosing is individualized based on INR measurements.

Geriatric: Start at lower end of dosing range due to increased bleeding risk.

Renal Impairment: Adjustments generally not required, but monitor closely.

Hepatic Impairment: Use with caution; hepatic function affects coagulation factors.

Pharmacokinetics

Absorption: Well absorbed orally.

Distribution: Wide distribution; crosses the placenta and is present in breast milk.

Metabolism: Hepatic metabolism mainly via CYP2C9.

Excretion: Metabolites excreted in urine and feces.

Half Life: Approximately 20-60 hours, varies among individuals.

Contraindications

Known hypersensitivity to warfarin
Active bleeding, including bleeding peptic ulcers
Pregnancy (especially during the first trimester)

Precautions

Use with caution in hepatic or renal impairment, hypertension, alcoholism, or in elderly patients; monitor INR regularly. Risk of bleeding.

Adverse Reactions - Common

Bleeding (Common)
Bleeding gums (Common)

Adverse Reactions - Serious

Hemorrhage (e.g., intracranial, gastrointestinal) (Serious but less common)
Skin necrosis (Rare)
Purple toe syndrome (Rare)

Drug-Drug Interactions

Antiplatelet agents, NSAIDs, other anticoagulants, certain antifungals, antidepressants, antibiotics that inhibit CYP2C9

Drug-Food Interactions

Foods high in vitamin K (e.g., green leafy vegetables) can decrease efficacy

Drug-Herb Interactions

St. John’s Wort, ginkgo biloba, garlic, ginseng (may increase bleeding risk)

Nursing Implications

Assessment: Assess for bleeding, monitor INR regularly, assess dietary vitamin K intake.

Diagnoses:

Risk for bleeding

Implementation: Administer with consistent vitamin K intake, adjust dose based on INR, educate patient on bleeding precautions.

Evaluation: Maintain INR within therapeutic range (typically 2.0–3.0) for the indication.

Patient/Family Teaching

Report unusual bleeding or bruising immediately.
Maintain consistent intake of vitamin K-rich foods.
Avoid alcohol and herbal supplements without consulting healthcare provider.
Use soft toothbrush and electric razor to minimize bleeding risk.

Special Considerations

Black Box Warnings:

Significant and sometimes fatal bleeding risk.
Pregnancy category X: contraindicated during pregnancy—especially during the first trimester—due to risk of fetal bleeding and teratogenicity.

Genetic Factors: CYP2C9 and VKORC1 genetic variations affect dosing.

Lab Test Interference: Warfarin affects INR, which is used to monitor therapy.

Overdose Management

Signs/Symptoms: Excessive bleeding, hematuria, hematomas, hemoptysis.

Treatment: Discontinue warfarin; administer vitamin K (phytonadione); in severe cases, consider fresh frozen plasma or prothrombin complex concentrates.

Storage and Handling

Storage: Store at room temperature, protected from light and moisture.

Stability: Stable under recommended conditions, check expiration date.