Warfarin 🩸
Concise reference for warfarin: indications, INR targets, monitoring, interactions, and safety. Use the embedded tool for elevated INR/bleeding management.
About Warfarin (Quick Overview)
- Vitamin K antagonist (VKA) used for prevention/treatment of thromboembolism (e.g., AF, VTE, some mechanical valves).
- Narrow therapeutic index — dosing individualized; always follow local protocols and anticoagulation clinic guidance.
- Embedded tool below covers elevated INR and bleeding management including PCC dosing.
INR Targets & Monitoring (check local policy)
- Typical targets: AF/VTE usually INR 2.0–3.0; some mechanical heart valves 2.5–3.5 (valve-specific).
- Initiation/stability: frequent INR checks (daily–every few days) until stable, then usually every 4–8 weeks.
- After any reversal or major change (drug/diet/illness), recheck INR sooner (often within 24–72 h) per local guidance.
Key Interactions & Factors
- ↑ INR (bleeding risk): macrolides, azoles, metronidazole, trimethoprim–sulfamethoxazole, amiodarone, many antibiotics; acute alcohol binge; liver disease.
- ↓ INR (clotting risk): rifampicin, carbamazepine, phenytoin (variable), St John’s wort; high vitamin K intake changes.
- Diet: keep vitamin K intake consistent (leafy greens). Illness (vomiting/diarrhoea), fever, thyroid/liver disease can shift INR.
Patient Advice & Safety
- Missed dose: take when remembered on the same day; if next day, skip — do not double. Record and inform clinic.
- Warning signs: unusual bruising/bleeding, black stools, haematuria, severe headache/neuro signs — seek urgent review.
- Pregnancy: generally contraindicated — urgent specialist advice if pregnancy planned or suspected.
- Carry an anticoagulant alert card/bracelet and keep an up-to-date medication list.
🔗 Related & Resources
Warfarin Bleeding & Reversal Tool
For trained clinicians. Always follow local/hospital protocols.
Bleeding Risk Factors
Higher risk when INR >5:
- Age >70
- Previous bleeding complications
- GI ulcers/haemorrhage
- Prior CVA
- Recent surgery
- Uncontrolled blood pressure
- Recent initiation of anticoagulants
Reversal Plan
Warfarin – Reversal & Bleeding Plan
No bleeding.
Enter INR to view specific actions.
No intervention required until further information; continue routine INR monitoring per local protocol.
Additional Information
Most over‑anticoagulated patients return to therapeutic range within ~3 days of stopping warfarin.
Monitor: repeat INR per above; more frequent if PCC given (30–60 min, ~6 h, then as guided).
Follow local policy; doses may vary by hospital protocol. Discuss prosthetic valve cases with cardiology/haematology.
Warfarin Dosing Tool
Initiation & maintenance dosing guidance
Dosing Plan
Warfarin Initiation Plan
Day: 1
Sensitive: No
INR: —
Suggested dose: 5–7.5 mg
Rules: if INR ↑ >0.5 consider ↓ dose; if INR ↑ ≥1.0 consider holding 1 dose.
Guidance tool only. Individualise per clinical scenario. Prefer home tablet strength at discharge; if changed, counsel and update pharmacy records.