Redefining the Threshold for Permeability Classification
According to the 2000 FDA BCS Guidance, a compound that is classified as Class I (highly soluble, highly permeable) is eligible for a BCS biowaiver, which means that a clinical bioequivalence study is unnecessary in case of a new formulation or a generic version of the same chemical entity, for example. Even without a formal biowaiver, the FDA has more recently taken the position that clinical drug-drug interaction studies are unnecessary for highly permeable and highly soluble compounds that are also substrates of drug efflux transporters such as P-gp.
The in vitro permeability threshold defined by Absorption Systems’ High Permeability Internal Standard (HPIS) is the lowest available. This novel internal standard has a Papp about 7-fold lower than that of metoprolol (another compound often used for the same purpose) and fraction absorbed >95% in humans. With our standard, it is more likely that your compound will be classified as highly permeable, and this can simplify and accelerate your clinical testing.