What is the procedure for starting patients on Coumadin (warfarin)?

Starting Patients on Coumadin (Warfarin)

Initial Dosing Strategy

For outpatients sufficiently healthy to be treated outside the hospital, start warfarin at 10 mg daily for the first 2 days, then adjust based on INR measurements. 1

• This 10 mg loading approach achieves therapeutic INR faster than 5 mg initiation (4.2 vs 5.6 days mean time to therapeutic range), with 86% of patients therapeutic by day 5 compared to only 45% with 5 mg dosing 1
• However, for elderly, debilitated, or high bleeding-risk patients, start with lower doses of 2-4 mg daily 2
• The American College of Cardiology notes that elderly patients require approximately 1 mg/day less than younger individuals due to higher bleeding risk 3
• A standard 5 mg daily starting dose is also acceptable and produces satisfactory anticoagulation within 4-6 days for most patients 2

Concurrent Heparin Bridging

When rapid anticoagulation is required, start heparin (unfractionated or LMWH) concurrently with warfarin on day 1 and continue for at least 4-5 days until therapeutic INR is achieved. 1, 2

• Warfarin should be initiated on the first or second day of heparin therapy rather than waiting, which shortens hospital stays without increasing thromboembolism risk 1
• Early warfarin initiation (day 1-2 of heparin) reduces hospital utilization by approximately 4 days compared to delayed initiation 1
• Continue heparin overlap until INR is therapeutic (≥2.0) for at least 24 hours and preferably 2 consecutive days 1

INR Monitoring Schedule

Check INR daily until therapeutic range (2.0-3.0 for most indications) is reached and sustained for 2 consecutive days. 2

• After achieving stable therapeutic INR, monitor 2-3 times weekly for 1-2 weeks 2
• Once stable on maintenance dose, check INR every 3-4 days initially 3
• Long-term stable patients can have INR checked as infrequently as every 4 weeks 2, 3

Target INR Ranges

For most indications including atrial fibrillation, venous thromboembolism, and stroke prevention, target INR 2.0-3.0. 3

• Mechanical prosthetic valves may require higher intensity (INR 2.5-3.5 or 3.0-4.0 depending on valve type and position) 1, 3
• Higher intensity anticoagulation (INR 3.0-4.5) is dangerous for secondary stroke prevention and should be avoided 3

Special Population Considerations

Chronic Kidney Disease/ESRD

• Patients with CKD stages 3-5 and ESRD require approximately 20% lower warfarin doses compared to those with normal kidney function 4
• These patients may achieve therapeutic INR faster than those with normal renal function 4

Pregnancy

• Warfarin is absolutely contraindicated in pregnancy due to teratogenic effects and fetal hemorrhage risk 5
• For pregnant patients with mechanical heart valves, if warfarin dose ≤5 mg/day, continuation throughout pregnancy may be reasonable after informed consent (embryopathy risk <3%) 2, 3
• If warfarin dose >5 mg/day, switch to dose-adjusted LMWH during first trimester due to >30% fetal loss/embryopathy risk 2, 3

Critical Pitfalls to Avoid

Do not use loading doses when restarting warfarin after interruption, as this increases hemorrhagic risk without providing faster protection. 3

• Unexpected INR fluctuations commonly occur due to changes in diet (especially vitamin K intake), concurrent medications, poor compliance, or alcohol consumption 2
• A disproportionate number of thromboembolic and bleeding events occur when INR is outside therapeutic range 2
• Avoid high-dose vitamin K (>5 mg) in patients with high thromboembolic risk, as it causes prolonged warfarin resistance 3
• Avoid subcutaneous vitamin K due to unpredictable and delayed absorption 3
• Reserve IV vitamin K for life-threatening bleeding only due to anaphylaxis risk 3

Contraindications

Warfarin is contraindicated in: pregnancy, active bleeding, recent CNS/eye surgery, hemorrhagic tendencies, inadequate laboratory monitoring facilities, unsupervised patients with senility/alcoholism/psychosis, and spinal procedures 5