Plasma protein binding can influence the tissue distribution, clearance and pharmacological effects of drugs. QPS performs plasma protein binding assays using equilibrium dialysis or ultrafiltration at the drug discovery stage, as well as more thorough studies for regulatory submissions.

Early-stage studies focus on higher assay throughout. LC/MS/MS assays based on peak area ratios without calibration curve are often used. Protein binding studies for regulatory submission purpose typically use LC/MS/MS assays with a one-day mini-validation. QPS also performs protein binding studies using radiolabeled compounds.

More thorough studies characterize the time to equilibrium, stability, volume shift, and recovery during the protein binding method establishment. The study design may include concentration-dependence, species difference, and other factors that influence protein binding results. Some sponsors choose to investigate potential drug interactions using in vitro protein binding displacement assays, and we can accommodate these as well.

Ultrafiltration is an alternative method if the test article does not have an adsorption issue; and may be useful for compound which is not stable during equilibrium dialysis.