Warfarin

Warfarin

Drug monograph · NCLEX study reference
Trade names	Coumadin
Therapeutic class	Anticoagulant
Pharmacologic class	Vitamin K antagonist (NTI)
Onset / peak / duration	Onset 24 to 72 hours; full effect 5 to 7 days; long duration.
Half-life / level	Half-life 20 to 60 hours; monitored by INR (goal usually 2 to 3, or 2.5 to 3.5 for mechanical valves).
Routes	PO (oral)
High-alert (ISMP)	Yes
Black box warning	Yes (see Safety)
Antidote / reversal	Vitamin K (phytonadione); fresh frozen plasma or prothrombin complex concentrate for urgent reversal.
Pregnancy / lactation	Contraindicated in pregnancy.

Nursing pharmacology study reference (NCLEX-style monograph). Numeric values are standard teaching ranges for study and must be verified against current manufacturer labeling before clinical use. This is educational content, not prescribing guidance.

Warfarin (brand name Coumadin) — Anticoagulant; Vitamin K antagonist (NTI).

Identification

• Therapeutic class: Anticoagulant.
• Pharmacologic class: Vitamin K antagonist (NTI).

Pharmacology

• Mechanism of action: Inhibits vitamin K-dependent clotting factors (II, VII, IX, X), reducing clot formation; full effect takes days.
• Onset / peak / duration: Onset 24 to 72 hours; full effect 5 to 7 days; long duration.
• Half-life / therapeutic level: Half-life 20 to 60 hours; monitored by INR (goal usually 2 to 3, or 2.5 to 3.5 for mechanical valves).

Clinical use

• Indications: Atrial fibrillation, venous thromboembolism, mechanical heart valves, clot prevention.
• Usual dose, route, frequency: PO once daily, dosed to INR.
• Maximum dose / adjustments: Individualized to INR; many diet and drug interactions; bridge with heparin when starting for acute clots.

Safety

• Contraindications: Active bleeding, pregnancy (teratogenic), severe hepatic disease, recent or planned major surgery.
• Black box warning: Can cause major or fatal bleeding; regular INR monitoring is essential.
• Interactions: Numerous; antibiotics and amiodarone (raise INR), vitamin K-rich foods (green leafy vegetables lower INR, keep intake consistent), NSAIDs and antiplatelets (bleeding), alcohol, many herbals (ginkgo, garlic, ginseng, St. John's wort).
• Pregnancy / lactation: Contraindicated in pregnancy.
• High-alert: Yes.

Adverse effects

• Common side effects: Bruising, minor bleeding.
• Serious effects to report: Major bleeding, skin necrosis (early), purple toe syndrome.
• Antidote / reversal: Vitamin K (phytonadione); fresh frozen plasma or prothrombin complex concentrate for urgent reversal.

Nursing process

• Assessment before administration: Baseline INR, bleeding risk, diet, interacting drugs, pregnancy status.
• Interventions during therapy: Monitor INR regularly; teach consistent vitamin K intake; review every new drug for interactions.
• Monitor: INR, signs of bleeding, hemoglobin.
• Evaluation / expected outcome: INR in range without bleeding.

Patient teaching

• Patient teaching: Keep INR appointments; keep green vegetable intake steady (do not stop, just be consistent); use a soft toothbrush and electric razor; report bleeding; tell all providers.
• Notify provider if: Unusual bleeding or bruising, black or red stools, severe headache, blood in urine.
• Administration tips: Same time daily; consistent diet; frequent INR checks.