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Scaling factors
A strategy for the scaling of in vitro drug metabolism data to whole liver intrinsic clearance is illustrated in Figure 4.
Figure 4. Scaling procedure for converting data from various in vitro CYP enzyme systems to whole organ hepatic clearance.
The relevant scaling factors are milligrams of microsomal protein per gram of liver (MPPGL; Barter et al., 2006), hepatocellularity (HHEP; Barter et al., 2006), enzyme abundances (Rowland-Yeo et al., 2003) and total liver weight (Johnson et al., 2005).
Each of these scaling factors has been the subject of extensive, in-house meta-analysis of literature data.
They all exhibit significant inter-subject variability, including covariation with age.
