Caco-2 cell monolayers from a Bock et al. (14) in a 12-well, 21-day assay, b Lentz et al. in a six-well, 4-day assay (53), and c Withington (54) in a 24-well, 3-day assay. Triangle HP drugs, Circle LP drugs, Dashed line LP/HP boundary, Dotted line 90% absorption