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In vitro correction factors
In addition to the application of scaling factors, the accurate extrapolation of in vitro data to whole organ clearance requires the use of relevant correction factors.
When using data obtained with microsomes (HLM, rCYP, rUGT), an estimate of the free fraction in the microsomal incubation matrix (fumic) is required to correct for non-specific binding. A similar correction factor (fuinc) can also applied to data generated using cells.
When using data obtained with recombinant enzymes, it is also necessary to allow for any difference in activity per unit enzyme relative to that of the native enzyme within an organ. This is achieved by applying an Intersystem Extrapolation Factor (ISEF).
Protein scalars for cytosol and S9 in the liver and intestine are provided within the Simulator and in-house scaling values can be used for kidney cytosyol or S9 CLint data.
