What is the initial dosing of warfarin (Coumadin) in pediatric patients?

From the Guidelines

The starting dose of warfarin in children is typically 0.2 mg/kg orally on the first day, with subsequent dose adjustments made according to an INR nomogram, as recommended by the American College of Chest Physicians evidence-based clinical practice guidelines 1.

Key Considerations

• The dose is lower than adult dosing due to children's different pharmacokinetics and pharmacodynamics.
• For neonates and infants under 12 months, an even more conservative approach is recommended, but the initial dose is still 0.2 mg/kg orally on the first day if the baseline INR is 1.0 to 1.3 1.
• After initiating therapy, frequent INR monitoring is essential, typically checking the INR after 3-5 days and adjusting the dose accordingly to reach the target INR (usually 2.0-3.0 for most indications) 1.
• Dose adjustments should be made in small increments of 10-20% of the total weekly dose.
• Factors that may affect warfarin dosing in children include age, weight, diet (especially vitamin K intake), concurrent medications, and underlying medical conditions.
• Parents should be educated about maintaining consistent vitamin K intake through diet, avoiding medications that interact with warfarin (such as NSAIDs), and recognizing signs of bleeding.
• Warfarin comes in multiple tablet strengths, allowing for precise dosing adjustments.

Dose Adjustment Guidelines

• If the INR is 1.1-1.3, repeat the initial loading dose 1.
• If the INR is 1.4-1.9, give 50% of the initial loading dose 1.
• If the INR is 2.0-3.0, give 50% of the initial loading dose 1.
• If the INR is 3.1-3.5, give 25% of the loading dose 1.
• If the INR is >3.5, hold dosing until INR is <3.5, then restart at 20% less than the last dose 1.

From the FDA Drug Label

PEDIATRIC USE Safety and effectiveness in pediatric patients below the age of 18 have not been established, in randomized, controlled clinical trials. However, the use of warfarin sodium tablets in pediatric patients is well-documented for the prevention and treatment of thromboembolic events. Difficulty achieving and maintaining therapeutic PT/INR ranges in the pediatric patient has been reported. More frequent PT/INR determinations are recommended because of possible changing warfarin requirements. The FDA drug label does not answer the question.

From the Research

Starting Dose of Warfarin in Children

• The initial dosage of warfarin in children is recommended to be 0.1 mg/kg/d, as stated in the study 2.
• This dose is intended to provide anticoagulation without significant adverse effects, and dosing should be adjusted to achieve a target international normalized ratio (INR) 2.
• The target range for INR values in children is not well established, but values of 1.5-3 are recommended for most patients, with higher values used in children with prosthetic cardiac valves and hereditary clotting disorders 2.
• Factors such as age, clinical condition, and route of administration of warfarin can influence the response to oral anticoagulation in children, and may require adjustments to the starting dose or maintenance dose 3.
• The use of computerized software programs to assist with warfarin dosing can improve the percentage of time that children with cardiac disease remain within the target therapeutic range, and may help to reduce the risk of adverse events 4.