Warfarin Management Algorithm

Initial Dosing Strategy

Elderly patients require approximately 1 mg/day less than younger individuals due to higher bleeding risk, according to the American College of Cardiology 1

For most indications including atrial fibrillation, venous thromboembolism, and stroke prevention, the American College of Cardiology recommends targeting INR 2.0-3.0 2
Mechanical prosthetic valves may require higher intensity anticoagulation (INR 2.5-3.5 or 3.0-4.0 depending on valve type and position), as suggested by the American College of Cardiology 2
Higher intensity anticoagulation (INR 3.0-4.5) is dangerous for secondary stroke prevention and should be avoided, according to the American College of Cardiology 3

Once stable on maintenance dose, the American College of Cardiology recommends checking INR every 3-4 days initially 1
Long-term stable patients should have their INR checked every 4 weeks, as recommended by the American College of Cardiology 2

For INR above therapeutic range but <5.0, the American College of Cardiology suggests reducing or omitting the next dose and resuming at a lower dose when INR approaches therapeutic range 2
For INR 5.0-9.0 without bleeding, the American College of Cardiology recommends omitting the next 1-2 doses of warfarin and giving oral vitamin K₁ 1-2.5 mg if the patient has bleeding risk factors 2
Oral vitamin K₁ 1 mg reduces INR to <4 in 85% of patients within 24 hours, according to the American College of Cardiology 2

The American College of Cardiology recommends restarting warfarin immediately at 50-75% of the previous maintenance dose once INR normalizes, with close monitoring 1
The American College of Cardiology suggests not using loading doses when restarting warfarin, as this increases hemorrhagic risk without faster protection 1

The American College of Cardiology advises against using high-dose vitamin K (>5 mg) in patients with high thromboembolic risk, as it causes prolonged warfarin resistance 2
The American College of Cardiology recommends avoiding subcutaneous vitamin K, as absorption is unpredictable and delayed 2
The American College of Cardiology suggests reserving IV vitamin K for life-threatening bleeding only, due to the risk of anaphylaxis 2

The American College of Cardiology recommends that warfarin ≤5 mg/day throughout pregnancy has <3% embryopathy risk 6
The American College of Cardiology suggests switching to dose-adjusted LMWH if warfarin >5 mg/day in the first trimester, due to >30% fetal loss/embryopathy risk 6

The American College of Cardiology states that warfarin is safe during breastfeeding, as it does not induce anticoagulant effect in the infant 3