Received for publication February 10, 2005.
Revised June 2, 2005.
Accepted for publication June 2, 2005.

A Novel Model for Prediction of Human Drug Clearance by Allometric Scaling

Abstract

Sixty-one sets (61) of clearance (CL) values in animal species were allometrically scaled for predicting human clearance. Unbound fraction (f_u) of drug in plasma in rats and humans were obtained from the literature. A model was developed to predict human CL: CL = 33.35 (ml/min)x(a/Rf_u)^0.770, where Rf_u is the f_u ratio between rats and humans and a is the coefficient obtained from allometric scaling. The new model was compared with simple allometric scaling and the 'rule of exponents'(ROE). Results indicated that the new model provided better predictability for human values of CL than ROE. It is especially significant that for the first time the proposed model improves the prediction of CL for drugs illustrating large vertical allometry.

Key words: drug clearance, in vitro-in vivo scaling, pharmacokinetics, plasma protein binding

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