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Warfarin Uses, Dosage, Side Effects & Warnings | DrugsAtlas

Authoritative Clinical Reference

Therapeutic Class

Anticoagulant

Subclass

Vitamin K Antagonist (Coumarin derivative)

Speciality

Cardiology

Schedule (India)

Schedule H

Routes

Oral

Formulations

Tablets: 1 mg, 2 mg, 3 mg, 5 mg
Note: Not all strengths uniformly available across all pharmacies; 2.5 mg tablets available from select manufacturers

Adult indications

INDICATIONS + DOSING — FOR CLINICIAN USE ONLY

Primary Indications (Approved / Standard in India)

1. Venous Thromboembolism (VTE) — Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE)

Parameter	Recommendation
Starting dose	5 mg once daily for first 2 days; use 2–3 mg in elderly, hepatic impairment, malnutrition, or high bleeding risk
Overlap therapy	Initiate concurrently with LMWH/UFH; overlap for minimum 5 days AND until INR ≥2.0 for at least 24 hours
Titration	Adjust based on INR response; target INR 2.0–3.0
Usual maintenance dose	2–10 mg once daily (highly variable; INR-guided)
Maximum dose	No fixed maximum; dose determined by INR target

Duration of Therapy:

Scenario	Duration
First VTE provoked by transient risk factor	3 months
First unprovoked VTE	3–6 months minimum; consider extended therapy
Recurrent unprovoked VTE	Indefinite (lifelong) with annual bleeding risk reassessment
VTE with active malignancy	LMWH preferred; warfarin if LMWH not feasible — continue while cancer active

2. Atrial Fibrillation (Valvular and Non-valvular)

Parameter	Recommendation
Starting dose	3–5 mg once daily; 2–3 mg in elderly or high-risk patients
Titration	Based on INR; check INR on day 3–5, then adjust
Target INR	2.0–3.0 for most patients
Usual maintenance dose	INR-guided (typically 2–7 mg/day)
Maximum dose	Not applicable — INR-guided

Clinical Notes:

Use CHA₂DS₂-VASc score to determine need for anticoagulation
Use HAS-BLED score for bleeding risk assessment annually
Long-term/lifelong therapy in most cases
Non-valvular AF: DOACs may be considered as alternative where appropriate

3. Mechanical Prosthetic Heart Valves

Valve Position	Target INR	Additional Notes
Aortic valve (bileaflet/tilting disc, no risk factors)	2.0–3.0	Lower intensity acceptable in low-risk cases
Aortic valve with risk factors (AF, LV dysfunction, prior thromboembolism)	2.5–3.5	Add low-dose aspirin (75–100 mg) in high-risk
Mitral valve (any type)	2.5–3.5	Higher thrombogenic potential
Multiple valves or older generation valves	2.5–3.5	Consult cardiology

Parameter	Recommendation
Starting dose	3–5 mg once daily
Titration	INR-guided; check frequently until stable
Usual maintenance dose	Individualised; typically 3–8 mg/day
Duration	Lifelong

Clinical Notes:

LMWH bridging required perioperatively
DOACs are contraindicated in mechanical valves
Regular dental prophylaxis advised

4. Rheumatic Mitral Valve Disease with Atrial Fibrillation

Parameter	Recommendation
Starting dose	3–5 mg once daily
Titration	INR-guided
Target INR	2.0–3.0
Usual maintenance dose	INR-guided
Duration	Long-term/lifelong

Clinical Notes:

Classified as valvular AF; DOACs not recommended
Warfarin remains standard of care in India for rheumatic valvular disease

Secondary Indications — Adults (Off-label)

Indication	Dose	Duration	Notes
Antiphospholipid Syndrome (APS) with thrombosis	Target INR 2.0–3.0 (standard); INR 3.0–4.0 in recurrent arterial events (controversial)	Lifelong	OFF-LABEL — Specialist only; evidence from international guidelines and Indian rheumatology practice
Cardioembolic Stroke (secondary prevention)	Target INR 2.0–3.0	Long-term based on aetiology	OFF-LABEL — Initiate 4–14 days post-stroke depending on infarct size and haemorrhagic transformation risk; specialist decision
Left Ventricular Thrombus post-MI	Target INR 2.0–3.0	3–6 months or until thrombus resolution on imaging	OFF-LABEL — Used in Indian cardiology practice; echocardiographic follow-up required
Dilated Cardiomyopathy with severe LV dysfunction and AF/thrombus	Target INR 2.0–3.0	Long-term	OFF-LABEL — Specialist only

Paediatric indications

PAEDIATRIC DOSING (Specialist Only)

Primary Indications

Approved uses: Mechanical prosthetic heart valves, VTE treatment/prophylaxis, Fontan circulation, cardiac shunts, Kawasaki disease with coronary aneurysms

Age Group	Starting Dose	Titration	Target INR	Monitoring
Neonates (<1 month)	0.2 mg/kg once daily	Adjust based on INR; check day 2–3	Indication-dependent	INR every 1–2 days initially
Infants/Children (1 month – 12 years)	0.2 mg/kg once daily (max initial dose 5 mg)	Adjust based on INR	VTE: 2.0–3.0; Mechanical valve: 2.5–3.5	INR every 2–3 days → weekly → monthly
Adolescents (>12 years)	3–5 mg once daily (similar to adult)	INR-guided	As per indication	As per adult protocol

INR Targets by Indication (Paediatric):

Indication	Target INR
VTE (primary or secondary)	2.0–3.0
Mechanical mitral valve	2.5–3.5
Bioprosthetic valve (first 3 months)	2.0–3.0
Fontan/cavopulmonary shunt	2.0–3.0
Kawasaki with giant aneurysms	2.0–3.0 (often with aspirin)

Safety and Monitoring:

Monitor INR every 2–3 days until stable, then every 1–2 weeks, then monthly
Educate caregivers on bleeding signs, dietary consistency, drug interactions
Vitamin K intake counselling essential
Liquid formulations not commercially available; extemporaneous preparation may be needed

Secondary Indications — Paediatrics (Off-label)

Indication	Dose	Duration	Notes
Antiphospholipid syndrome (paediatric)	0.1–0.2 mg/kg/day; target INR 2.0–3.0	Long-term	OFF-LABEL — Specialist only; managed by paediatric rheumatology/haematology
Catheter-related thrombosis (prolonged)	Weight-based; INR 2.0–3.0	3–6 months post catheter removal	OFF-LABEL — Specialist only

Age Restriction Statement:

NOT RECOMMENDED in neonates <1 month except under experienced paediatric haematology or cardiology specialist supervision
Extreme caution required in preterm infants due to immature hepatic metabolism

Renal Adjustments

Renal Function	Recommendation
Mild-moderate CKD (eGFR 30–60)	No specific dose adjustment; monitor INR more frequently due to increased bleeding risk
Severe CKD (eGFR <30)	Use with caution; increased bleeding tendency; INR may be less stable
ESRD / Haemodialysis	Warfarin is NOT dialysed; can be used in dialysis patients with mechanical valves or valvular AF; preferred over DOACs in this population
Peritoneal dialysis	No adjustment; INR monitoring as usual

Clinical Note: Warfarin preferred over DOACs in patients with eGFR <15 mL/min or on dialysis requiring anticoagulation for valvular indications.

Hepatic adjustment

Contraindications

Active clinically significant bleeding (GI, intracranial, retroperitoneal, etc.)
Haemorrhagic stroke (recent or ongoing)
Severe uncontrolled hypertension (>180/110 mmHg)
Pregnancy — 1st trimester (teratogenic) and last 4 weeks (delivery-related bleeding risk)
Known hypersensitivity to warfarin or any coumarin derivative
Inability to monitor INR reliably (non-compliance, remote access issues)
Severe thrombocytopenia (<50,000/μL)
Recent or planned neurosurgical, ophthalmic, or spinal procedures (within 72 hours)
Unsupervised alcoholism with poor compliance

Cautions

Hepatic disease — enhanced anticoagulant effect
Malnutrition or vitamin K deficiency — increased sensitivity
Congestive heart failure — may affect hepatic metabolism
Hyperthyroidism — increases warfarin catabolism of clotting factors; may need dose adjustment
Elderly with fall risk — increased intracranial bleeding risk
Recent surgery or trauma
Active peptic ulcer disease (even if not currently bleeding)
Polypharmacy — multiple drug interactions affecting INR
Inconsistent dietary vitamin K intake
Diarrhoeal illness — may alter vitamin K absorption and warfarin effect
Protein C or S deficiency — risk of warfarin-induced skin necrosis at initiation; bridge with heparin

Pregnancy

Aspect	Recommendation
Risk category	Contraindicated in 1st trimester and near term (Risk category: D/X depending on timing)
Fetal risks	1st trimester: Fetal warfarin syndrome (nasal hypoplasia, stippled epiphyses, limb hypoplasia, CNS abnormalities) — risk 5–10% with exposure weeks 6–12
2nd–3rd trimester risks	Fetal/neonatal haemorrhage, CNS abnormalities
Preferred alternatives	LMWH (enoxaparin) throughout pregnancy in most cases
When warfarin may be used	High-risk mechanical heart valves where LMWH deemed inadequate — specialist decision only; typically 2nd trimester with LMWH in 1st trimester and last 4 weeks
Monitoring	Fetal anatomy scan at 18–22 weeks, serial growth scans, maternal INR, delivery planning with haematology/cardiology

Lactation

Aspect	Recommendation
Compatibility	Compatible with breastfeeding
Drug levels in milk	Minimal/negligible — warfarin is highly protein-bound; transfer to breast milk is clinically insignificant
Preferred alternatives	Not required; warfarin is considered safe
Infant monitoring	Routine observation; monitor for unusual bruising or bleeding only if mother's INR is significantly supratherapeutic

Elderly

Aspect	Recommendation
Starting dose	2–3 mg once daily (lower than standard adult dose)
Titration	Slower; assess INR more frequently (every 2–3 days initially)
Usual maintenance	Often lower than younger adults (typically 2–5 mg/day)
Special risks	Increased bleeding risk (falls, GI bleed, intracranial haemorrhage); polypharmacy; impaired renal function; cognitive impairment affecting compliance
Recommendations	Fall risk assessment; medication reconciliation; caregiver education; consider pill organizers; frequent INR checks

Major drug interactions

Drug/Class	Effect on Warfarin/INR	Mechanism	Management
Rifampicin	↓↓ INR (marked reduction)	Potent CYP2C9/CYP3A4 inducer	Avoid combination; if essential, increase warfarin dose significantly (may need 2–3x); monitor INR frequently
Phenytoin, Carbamazepine, Phenobarbital	↓ INR	CYP inducers	Monitor INR; dose adjustment required
Amiodarone	↑↑ INR (marked increase)	CYP2C9 inhibition	Reduce warfarin dose by 30–50% when adding amiodarone; monitor INR weekly for 4–6 weeks
Fluconazole, Voriconazole, Ketoconazole	↑↑ INR	CYP2C9 inhibition	Reduce warfarin dose; frequent INR monitoring
Metronidazole	↑ INR	CYP inhibition	Reduce dose or use short course with monitoring
NSAIDs (regular use)	↑ Bleeding risk	Platelet inhibition + possible GI erosion	Avoid chronic use; if needed, use lowest dose with PPI cover and closer INR monitoring
Aspirin (>100 mg/day)	↑ Bleeding risk	Additive antiplatelet effect	Avoid unless specific indication (e.g., mechanical valve with high risk)
Cotrimoxazole (TMP-SMX)	↑ INR	CYP2C9 inhibition	Reduce warfarin; monitor closely

Moderate drug interactions

Drug/Class	Effect	Management
Macrolides (Erythromycin, Clarithromycin, Azithromycin)	↑ INR	Monitor INR during antibiotic course; may need dose reduction
Fluoroquinolones (Ciprofloxacin, Levofloxacin)	↑ INR	Monitor INR; reduce warfarin if needed
Cephalosporins (especially cefoperazone, ceftriaxone)	↑ INR	Vitamin K depletion; monitor INR
Paracetamol (>2 g/day regularly)	↑ INR (modest)	Monitor INR with chronic high-dose use
Levothyroxine	↑ Warfarin effect	Potentiates vitamin K-dependent factor catabolism; monitor INR after thyroid dose changes
SSRIs (Fluoxetine, Sertraline)	↑ Bleeding risk	Platelet dysfunction + possible CYP interaction; monitor for bleeding signs
Statins (some)	Variable; usually modest ↑ INR	Monitor INR when initiating or changing statin
Omeprazole	↑ INR (modest)	CYP2C19 interaction; usually minor; monitor
Herbal products (Garlic, Ginkgo, Ginger, Ginseng)	Variable INR effects	Counsel patients to maintain consistent intake; inform physician before use
Cranberry juice (large quantities)	↑ INR	Avoid excessive consumption

Common Adverse effects

Bleeding (minor) — gum bleeding, epistaxis, easy bruising, prolonged bleeding from cuts
Haematuria (microscopic or gross)
Menorrhagia
Nausea, vomiting
Diarrhoea or abdominal discomfort
Alopecia (with prolonged use)
Skin rash

Serious Adverse effects

Adverse Effect	Clinical Features	Management
Major haemorrhage (GI, intracranial, retroperitoneal)	Haematemesis, melaena, altered sensorium, severe headache, haematochezia, hypotension	Immediate cessation; IV Vitamin K 5–10 mg slow infusion; 4-factor PCC (preferred) or FFP; ICU admission; surgical intervention if indicated
Warfarin-induced skin necrosis	Painful purpuric skin lesions → necrosis; occurs days 3–8 of therapy; more common in protein C/S deficiency	Stop warfarin immediately; heparinisation; vitamin K; specialist dermatology/haematology input; may require debridement
Purple toe syndrome	Painful, purple discolouration of toes; cholesterol microembolism	Discontinue warfarin; supportive care
Calciphylaxis (rare, in CKD patients)	Painful, necrotic skin lesions	Stop warfarin; specialist nephrology input
Fetal warfarin syndrome	Nasal hypoplasia, skeletal abnormalities	Prevention — avoid in pregnancy

Monitoring requirements

Timing	Parameters
Baseline (before initiation)	PT/INR, aPTT, complete blood count, liver function tests, renal function, bleeding history assessment
After initiation	INR on day 2–3, day 5, then every 2–3 days until stable within therapeutic range
After dose adjustment	INR within 3–5 days of any dose change
Stable long-term therapy	INR every 2–4 weeks (depending on stability); at least monthly
Additional monitoring	Haemoglobin (periodically), signs of bleeding, medication reconciliation at each visit, dietary vitamin K consistency

INR Interpretation and Action:

INR Value	Action
<1.5	Increase dose; reassess compliance, diet, interactions
1.5–1.9	Increase dose modestly
2.0–3.0 (or target range)	Therapeutic; continue same dose
3.1–4.0	Reduce dose; recheck in 1 week; assess for bleeding
4.1–5.0	Hold 1 dose; reduce subsequent doses; recheck in 2–3 days
5.1–9.0 (no bleeding)	Hold warfarin; oral Vitamin K 1–2.5 mg if high bleeding risk; recheck daily
>9.0 (no bleeding)	Hold warfarin; oral Vitamin K 2.5–5 mg; recheck in 24–48 hours
Any INR with serious bleeding	Stop warfarin; IV Vitamin K 5–10 mg; 4-factor PCC or FFP; hospital admission

Brands in India

Warfarin Sodium Brands:

Warf (Cipla)
Sofarin (Samarth Pharma)
Uniwarfin (Unichem)
Marevan (Aspen — limited availability)
Warfarin (generic — various manufacturers)

Note:

Acitrom® contains acenocoumarol (NOT warfarin) — different VKA with shorter half-life
Do NOT interchange warfarin with acenocoumarol without re-titration of INR; different dosing and kinetics

Price range (INR)

Formulation	Approximate Price
Warfarin 1 mg tablet	₹1–2 per tablet
Warfarin 2 mg tablet	₹1.50–2.50 per tablet
Warfarin 5 mg tablet	₹2–4 per tablet

Notes:

Significantly cheaper than DOACs
Not included in NLEM 2022 (acenocoumarol is listed instead)
Available in government hospitals in most states
No NPPA price ceiling applicable

Clinical pearls

Always check baseline INR before initiating warfarin — do not assume it is normal, especially in liver disease or malnutrition.
LMWH bridging is mandatory at initiation — warfarin takes 4–5 days to achieve anticoagulant effect; continue LMWH until INR ≥2.0 for at least 24 hours on two consecutive measurements.
Dietary vitamin K counselling is essential — advise consistent (not restricted) intake of green leafy vegetables; erratic dietary changes cause INR fluctuations.
Do NOT switch between warfarin and acenocoumarol casually — different pharmacokinetics require complete INR re-stabilisation.
INR >10 without bleeding — give oral Vitamin K 2.5–5 mg and hold warfarin; do not panic or give high-dose IV vitamin K unless actively bleeding.
Perioperative management — for elective surgery, stop warfarin 5 days prior; bridge with LMWH if high thrombotic risk (mechanical valves, recent VTE); resume post-op when haemostasis secured.

Version

RxIndia v1.1 — 13 Jun 2025

Reference

CDSCO-approved prescribing information
Indian Pharmacopoeia 2022
API Textbook of Medicine (11th Edition)
AIIMS Anticoagulation Protocols
MoHFW NCD Guidelines — Atrial Fibrillation
ICMR Guidelines on Cardiovascular Disease Management
Harrison's Principles of Internal Medicine (21st Edition)
ACC/AHA Guidelines (for international reference where not conflicting with Indian practice)
NLEM 2022 (reference: acenocoumarol listed; warfarin in public hospital formularies)
Indian Society of Haematology and Blood Transfusion protocols

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