Comments on "a mathematical description of the functionality of correction factors used in allometry for predicting human drug clearance".

In a recent paper, Tang and Mayersohn [(2005) Drug Metab Dispos 33:1294-1296] mathematically described the functionality of the correction factors (CFs), maximum life-span potential (MLP), and brain weight (BrW) used in allometric scaling for the prediction of human drug clearance. They found that there is an intrinsic defect in using correction factors because different combinations of species will produce different prediction results. Analysis with real examples reveals that different predicted clearance values observed with different combinations of animal species, with or without CFs, are not due to the intrinsic defect of the correction factors; rather, it is the effect of the species, observed clearance values in the species, and the range of the body weights. Even if one does not use the CF, the predicted clearance by the simple allometry will still vary by severalfold, depending on the species used in the scaling.