Biopharmaceutics Classification System permeability measurements

Bioavailability depends not only on having the drug in solution, but also on the drug s permeability. A jejunal permeability of at least 2-4 x 10 4cm/s, measured in human subjects by intubation, is considered high [97]. For many drugs and other substances, this permeability corresponds to a fraction absorbed of 90% or better. Amidon et al. [97] thus proposed a Biopharmaceutics Classification System (BCS) for drugs based on the above definitions of these two parameters. Table 3 defines the BCS and includes some drugs representative of each class. 

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