External Evaluation of a Bayesian Warfarin Dose Optimization Based on a Kinetic-Pharmacodynamic Model

Area of Science:

• Pharmacokinetics and Pharmacodynamics
• Drug Dose Prediction
• Clinical Pharmacology

Background:

• Warfarin, a widely used anticoagulant, exhibits significant interindividual variability in dosage requirements.
• A previously established kinetic-pharmacodynamic (K-PD) model accurately predicts warfarin dose in Swedish patients.
• The applicability of this K-PD model to Japanese patient populations remains uninvestigated.

Purpose of the Study:

• To evaluate the predictive performance of a published K-PD model for warfarin dose requirements in Japanese patients.
• To assess the model's accuracy across diverse patient characteristics and clinical factors.
• To identify specific patient subgroups where the model's predictive accuracy may be limited.

Main Methods:

• A retrospective observational study at Tokyo Women's Medical University involving adult patients initiating warfarin therapy.
• Assessment of a modified Wright and Duffull K-PD model using prediction-corrected visual predictive checks.
• Bayesian parameter estimation and analysis of prothrombin time-international normalized ratio (PT-INR) data from 232 patients.

Main Results:

• The K-PD model demonstrated a tendency for underprediction of PT-INR in the Japanese patient cohort.
• Underprediction was more pronounced in patients over 60 years, with a body mass index ≤25 kg/m², or with estimated glomerular filtration rate ≤60 mL/min/1.73 m².
• Utilizing Bayesian prediction with four prior observations mitigated the underprediction issue.

Conclusions:

• The existing K-PD model requires modification for accurate warfarin dose prediction in Japanese patients, especially in specific subgroups.
• Further research is necessary to develop a tailored model for predicting warfarin dose requirements in Japanese populations.
• Optimizing warfarin dosing in diverse ethnic groups is crucial for effective anticoagulant therapy.