The use of IBH-5 decreased the kdeg values and increased the half-life of the compounds PNZ, TCP, Cpd I and Cpd II with kdeg values of 1.10 × 10-4 s- 1 (t1/2 = 115 min), 4 × 10-5 s-1 (t1/2 = 289 min), 4 × 10-5 s-1 (t1/2 = 289 min), and 3 × 10-5 s-1 (t1/2 = 385 min) respectively, compared to kdeg values of 1.25 × 10-2 s-1 (t1/2 = 0.9 min), 1.1 × 10-4 s-1 (t1/2 = 105 min), 1.0 × 10-3 s-1 (t1/2 = 11.5 min) and 4.5 × 10-4 s-1 (t1/2 = 26 min) in FBHThe use of lower temperature (4 °C) for the determination of fu,brain in this study is not successful due to the instability of the compounds during longer equilibration times required at lower temperatures.The fu,brain values for a set of 15 CNS drugs determined in FBH and IBH-5 using HT-dialysis were similar and are consistent with the literature values. The use of IBH-5 led to the determination of fu,brain for unstable compounds that could not be determined by other methods.The use of IBH-5 is an easy and convenient method to determine the fu,brain of unstable compounds in FBH during drug discovery and development.
Keywords: Fraction unbound; brain homogenate; equilibrium dialysis; inactivated brain homogenate; unstable.