From the Guidelines
The recommended initial dosing for Coumadin (warfarin) is 5 mg daily, with subsequent dose adjustments based on INR results, as stated in the European Heart Journal guidelines 1. The dosing for Coumadin (warfarin) is highly individualized and requires careful monitoring.
- Initial dosing typically starts at 5 mg once daily for most adults,
- with subsequent dose adjustments based on INR (International Normalized Ratio) results. The target INR range is usually 2.0-3.0 for most indications, though some conditions like mechanical heart valves may require a higher target of 2.5-3.5.
- Dose adjustments should be made gradually,
- Warfarin requires regular INR monitoring, initially daily until the therapeutic range has been achieved, then twice or three times weekly during the first 2 weeks and then once a week or less often depending on the stability of the INR results, as recommended by the European Heart Journal guidelines 1. Many factors affect warfarin metabolism including diet (especially vitamin K intake), medications, alcohol consumption, and certain medical conditions.
- Patients should maintain consistent vitamin K intake,
- avoid alcohol excess,
- and inform healthcare providers about all medications and supplements they take. Missed doses should be taken as soon as remembered on the same day, but double doses should never be taken. Due to the risk of serious bleeding, patients should report any unusual bleeding or bruising immediately to their healthcare provider. In patients with chronic kidney disease (CKD), the dose of warfarin may need to be adjusted, typically 20% lower in severe CKD, as suggested by the Journal of the American College of Cardiology guidelines 1.
From the FDA Drug Label
The dosing of warfarin sodium tablets must be individualized according to patient’s sensitivity to the drug as indicated by the PT/INR It is recommended that warfarin sodium tablets therapy be initiated with a dose of 2 to 5 mg per day with dosage adjustments based on the results of PT/INR determinations. Most patients are satisfactorily maintained at a dose of 2 to 10 mg daily.
The recommended dosing for Coumadin (warfarin) is to initiate therapy with a dose of 2 to 5 mg per day, with subsequent dosage adjustments based on the results of PT/INR determinations. The typical maintenance dose is 2 to 10 mg daily. 2
From the Research
Recommended Dosing for Coumadin (Warfarin)
The recommended dosing for Coumadin (warfarin) varies depending on the patient's condition and the target international normalized ratio (INR) range.
- For patients with atrial fibrillation, the target INR range is typically between 2.0 and 3.0 3.
- For patients with deep vein thrombosis, the target INR range is also between 2.0 and 3.0 3, 4.
- For patients with prosthetic heart valves, the target INR range may be higher, typically between 2.5 and 3.5 3.
Initiation of Warfarin Therapy
When initiating warfarin therapy, a loading dose should be avoided, and instead, warfarin should be initiated with a 5-mg dose (or 2 to 4 mg in the very elderly) 5, 4.
- The INR should be monitored frequently, typically 2 to 4 times per week, immediately after initiation of warfarin 5.
- The interval between INR tests can be lengthened gradually, up to a maximum of 4 to 6 weeks, in patients with stable INR values 5.
Adjusting Warfarin Dose
The warfarin dose should be adjusted based on the measured INR values and clinical factors 5.
- The dose does not need to be adjusted for a single INR that is slightly out of range 5.
- Most changes should alter the total weekly dose by 5% to 20% 5.
- Patients who have an elevated INR will need more frequent testing and may also require vitamin K1 5.
Special Considerations
For patients aged over 75 years, the target INR may be reduced to 2.0-2.5, or perhaps as low as 1.5-2.0, due to the increased risk of intracranial bleeding 3.
- In patients with AF, aspirin is less effective than warfarin, and the addition of aspirin (100 mg/day) further decreases the risk of embolism but increases the risk of gastrointestinal bleeding 3.