Comparison between the apparent permeability measured with the standard and the modified MDCK-MDR1 assay for a chemical series (N = 39). The standard permeability assay was performed as described in Section 2.3. The modified permeability assay with prolonged preincubation time is described above. All Papp values represent mean values of duplicates. Papp,Intrinsic ratio is calculated by dividing Papp,Intrinsic from the modified assay by Papp,Intrinsic from the standard assay. (A) Papp,Intrinsic values from the modified assay were plotted against Papp,Intrinsic values from the standard assay. Solid line shows 1:1 correlation. (B) Ratios between Papp,Intrinsic values from standard and modified assays were plotted against cLogP.