title: Allometric scaling of pharmacokinetic parameters in drug discovery: can human CL, Vss and t1/2 be predicted from in-vivo rat data?
abstract: In a drug discovery environment, reasonable go/no-go human in-vivo pharmacokinetic (PK) decisions must be made in a timely manner with a minimum amount of animal in-vivo or in-vitro data. We have investigated the accuracy of the in-vivo correlation between rat and human for the prediction of the total systemic clearance (CL), the volume of distribution at steady state (Vss), and the half-life (t1/2) using simple allometric scaling techniques. We have shown, using a large diverse set of drugs, that a fixed exponent allometric scaling approach can be used to predict human in-vivo PK parameters CL, Vss and t(1/2) solely from rat in-vivo PK data with acceptable accuracy for making go/no-go decisions in drug discovery. Human in-vivo PK predictions can be obtained using the simple allometric scaling relationships CL(Human) approximately = 40 CL(Rat) (L/hr), Vss(Human) approximately = 200 Vss(Rat) (L), and t1/2(Human) approximately = 4 t1/2(Rat) (hr). The average fold error for human CL predictions for N = 176 drugs was 2.25 with 79% of the drugs having a fold error less than 3. The average fold error for human Vss predictions for N = 144 drugs was 1.85 with 84% of the drugs having a fold error less than 3. The average fold error for human t1/2 predictions for N = 145 drugs was 2.05 with 76% of the drugs having a fold error less than 3. Using these simple allometric relationships, the sorting of drug candidates into a low/medium/high/very high human classification scheme was also possible from rat data. Since these simple allometric relationships between rat and human CL, Vss, and t1/2 are reasonably accurate, easy to remember and simple to calculate, these equations should be useful for making early go/no-go in-vivo human PK decisions for drug discovery candidates.
authors.affiliation: Johnson & Johnson Pharmaceutical Research and Development, L.L.C. Drug Discovery, Spring House, PA 19477, USA.
authors.forename: Gary W
authors.initials: GW
authors.lastname: Caldwell
authors.forename: John A
authors.initials: JA
authors.lastname: Masucci
authors.forename: Zhengyin
authors.initials: Z
authors.lastname: Yan
authors.forename: William
authors.initials: W
authors.lastname: Hageman
mesh_terms: D000465:Algorithms; D000818:Animals; D015195:Drug Design; D006207:Half-Life; D006801:Humans; D010599:Pharmacokinetics; D011237:Predictive Value of Tests; D051381:Rats; D012044:Regression Analysis; D013045:Species Specificity