Predictions of the in vivo clearance of drugs from rate of loss using human liver microsomes for phase I and phase II biotransformations.
OBJECTIVE
The utility of in vitro metabolism to accurately predict the clearance of hepatically metabolized drugs was evaluated. Three major goals were: (1) to optimize substrate concentration for the accurate prediction of clearance by comparing to Km value, (2) to prove that clearance of drugs by both oxidation and glucuronidation may be predicted by this method, and (3) to determine the effects of nonspecific microsomal binding and plasma protein binding.


METHODS
The apparent Km values for five compounds along with scaled intrinsic clearances and predicted hepatic clearances for eight compounds were determined using a substrate loss method. Nonspecific binding to both plasma and microsomal matrices were also examined in the clearance calculations.


RESULTS
The Km values were well within the 2-fold variability expected for between laboratory comparisons. Using both phase I and/or phase II glucuronidation incubation conditions, the predictions of in vivo clearance using the substrate loss method were shown to correlate with published human clearance values. Of particular interest, for highly bound drugs (>95% plasma protein bound), the addition of a plasma protein binding term increased the accuracy of the prediction of in vivo clearance.


CONCLUSIONS
The substrate loss method may be used to accurately predict hepatic clearance of drugs.
Department of Drug Disposition, Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46285, USA.
Michael A
MA
Mohutsky
Jenny Y
JY
Chien
Barbara J
BJ
Ring
Steven A
SA
Wrighton
D000465:Algorithms; D001711:Biotransformation; D001798:Blood Proteins / Q000378:metabolism; D020719:Glucuronides / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D013058:Mass Spectrometry; D008657:Metabolic Clearance Rate; D008862:Microsomes, Liver / Q000378:metabolism*; D010084:Oxidation-Reduction; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D010599:Pharmacokinetics; D011237:Predictive Value of Tests; D011485:Protein Binding
D001798:Blood Proteins; D020719:Glucuronides; D004364:Pharmaceutical Preparations