A Sequential Ultrafiltration Method to Enhance the Accuracy and Throughput in Plasma Protein Binding Tests

Objectives: Ultrafiltration (UF) is widely accepted as a method for assessing the plasma protein binding (PPB) of drugs. However, it is vulnerable to non-specific binding (NSB) to the device, which can result in inaccuracies. This study presents a straightforward, high-throughput modified UF method aimed at minimizing bias due to NSB. Methods: The modified UF method, sequential UF, features the addition of a 2 min pre-UF phase designed to saturate the NSB in the device, followed by the main 20 min UF procedure, compared to the conventional UF method. To evaluate the feasibility of this sequential UF method, we measured the PPB of nine compounds using sequential UF and compared these results to those obtained with the conventional mass balance UF method, recognized as a standard for NSB correction. Results: The PPB values determined through sequential UF were generally consistent with those derived from the mass balance UF method. The fold differences ranged from 97.9% to 113.8%, with an average of 103.5%. No significant differences were observed between the two methods for all compounds, with the exception of quercetin, which showed an unusually high PPB. Conclusions: Sequential UF was effective in correcting NSB to the device while providing advantages in terms of simplicity and efficiency.