Unfortunately, the information on whether intrinsic or apparent permeability is reported is not always properly described in the literature or databases (e.g., we had to implement PAMPA Pintr into MolMeDB upon preparation of this manuscript). The lack of distinction between apparent and intrinsic permeability can lead to complications, especially when comparing data from multiple papers using the PAMPA method. A similar lack of information affects cell-based methods. There is crucial information about the direction of measurement or membrane transport proteins. There are two possible directions -either from apical to basolateral (from A to B) or from basolateral to apical (from B to A). The difference of permeabilities in direction can be large, e.g. in Colabufo et al. . The direction affects the value of measured permeability because these cells have an asymmetrical expression of pharmacologically relevant proteins that influence molecular transport. These proteins are (i) efflux transporters, e.g., P-glycoprotein (MDR1, ABCB1), MRP2 (ABCC2) or BCRP (ABCG2), and (ii) uptake proteins, e.g., OCT2 (SLC22A2), OATP2B1 (SLCO2B1), or PEPT1 (SLC15A1) . In the case of these measurements, not only the direction in which the permeability is measured but also the presence of transporter inhibitors plays a role . The inhibitors increase the permeability of substrates of efflux transporters . Gene knockout techniques can also alter the expression of these transporters in the cells .