What are the key factors to consider when adjusting warfarin doses based on INR results?

When adjusting warfarin doses based on international normalised ratio (INR) results, key factors to consider include the current INR value relative to the therapeutic range, the trend of INR values over time, and the patient's clinical context including bleeding and thrombotic risks.

Specifically, dose adjustments should be guided by whether the INR is below, within, or above the target therapeutic range, typically 2.0 to 3.0 for most indications, but this may vary depending on the clinical scenario ¹.

Repeated INR values outside the therapeutic range, such as two INR values above 5 or one above 8 within six months, or two values below 1.5, indicate poor anticoagulation control and necessitate dose reassessment and possible intervention ².

Other important considerations include patient adherence to warfarin, concurrent illnesses, interacting medications, dietary vitamin K intake, and alcohol consumption, all of which can affect INR stability and warfarin metabolism ¹,².

When adjusting doses, it is essential to follow locally agreed protocols or specialist advice, considering the medicine’s summary of product characteristics (SPC) and individual patient factors such as renal function, cancer status, and body weight extremes ¹.

Calculating the time in therapeutic range (TTR) over a maintenance period of at least six months using validated methods (e.g., Rosendaal method) helps assess overall anticoagulation control and guides dose adjustments ².

In cases of poor INR control despite addressing modifiable factors, alternative anticoagulation strategies should be evaluated and discussed with the patient ².

Recent literature emphasizes the importance of individualized warfarin management, including careful monitoring and dose adjustments based on INR trends rather than isolated values, and highlights the need for patient education to improve adherence and reduce variability in INR (Witt et al., 2016).