Limitations were applied as described above to match

the reported CLint,P-gp(efflux) values ( Troutman and Thakker, 2003). A Simcyp “compound file” was created based on the reported physicochemical characteristics, protein ZD1839 solubility dmso binding and blood-to-plasma ratio for the compound buspirone (Gammans et al., 1986, Gertz et al., 2011 and Shibata et al., 2002). The “compound file” was then modified and used as a template to generate a set of virtual compounds from the combinations of the aforementioned parameters. The ionic class of the virtual compounds was set to be neutral in order to simplify the analysis and to reduce the number of combinations that could be derived from accounting for the different ionic classes. The drug’s XAV-939 manufacturer dissolution rate was estimated using the diffusion layer model built-into the Simcyp® ADAM model, where the drug was assumed to be a monodispersed powder with an initial particle radius of 30 μm. Peff values were estimated from the calculated Papp,Caco-2 values using the default method in the Simcyp® simulator for passively absorbed drugs ( Sun et al., 2002), Peff was kept constant throughout all the intestinal segments. Elimination was assumed to occur only by means of CYP3A4-mediated metabolism, both in the liver and the GI tract, which was estimated from the aforementioned enzyme kinetics parameters of CYP3A4. The fraction of drug unbound

in the enterocytes (fu,gut) was assumed to be

1 as per Yang et al. (2007). The rest of the parameters were kept as Simcyp® default values. The input parameters are summarized in Table S1 of the Supplementary Material. The virtual trials were simulated assuming a representative population. The values employed were those from the “healthy volunteers” population library within Casein kinase 1 Simcyp®, assuming no Libraries variability for the system parameters. A “minimal” PBPK model was used to describe the disposition and systemic elimination of the simulated compounds (Rowland Yeo et al., 2010). The oral dose was set to 30 mg, administered under fasted conditions together with 250 mL of water; with sampling up to 36 h post dose (Sakr and Andheria, 2001a and Sakr and Andheria, 2001b). Simulations were carried out using the Simcyp® Batch processor on a Dell OptiPlex 7010 PC (Intel Core i7-3770, 16 GB Ram) running Microsoft Windows 7 Enterprise (Dell Corp. Ltd., Berkshire, UK). In order to analyse the simulated data the study tree was sub-categorized into the four classes described in the BCS, thus leading to a reduction in the number of combinations analysed (from 78,125 to 12,500) by limiting the values for solubility and permeability from five to two values each. Selection of the solubility and permeability values was based on the BCS cut-off criteria for high/low soluble and permeable compounds.