Abstract
A novel and convenient method was established for the prediction of in vivo metabolic clearance in human liver. The present method applied the in vitro-in vivo extrapolation paradigm previously established in rats to the in vitro data obtained from cryopreserved human hepatocytes. Predicted hepatic availability and clearance were compared with the reported oral bioavailability and plasma clearance in humans for 14 clinically used drugs (naloxone, buspirone, verapamil, lidocaine, imipramine, metoprolol, timolol, antipyrine, diazepam, quinidine, caffeine, propranolol, diclofenac, and phenacetin). A large interindividual variation was observed in the intrinsic metabolic clearance among separate cryopreserved preparations from different subjects. The prediction generally resulted in a marked underestimation when the biologically based scaling factor (3.1 × 109cells/kg) was used for the extrapolation of in vitro data (milliliters per minutes per cells) to in vivo value (milliliters per minutes per kilograms). Reasonably good in vitro-in vivo correlations were obtained with empirically calculated scaling factors, 8.5 × 109 (cells/kg) from 10 individual preparations and 10.8 × 109 (cells/kg) from pooled preparation of two selected lots, which were 3- to 4-fold larger than the biologically based scaling factor. These data suggested that the calibration of inherent interindividual variation of metabolic activities among different cryopreserved preparations of human hepatocytes to obtain the empirical scaling factor, which is applicable only to the preparation used, was an essential step for more reliable and quantitative prediction of in vivo metabolic activity in humans.
Footnotes
- Abbreviations used are::
- HPLC
- high-performance liquid chromatography
- LC-MS/MS
- liquid chromatography-tandem mass spectrometry
- CLint, in vitro
- in vitro intrinsic clearance observed when test compounds were metabolized by human hepatocytes suspended in human serum
- D
- cell density of hepatocytes suspended in serum
- T
- incubation time
- R
- ratio of intact drug concentration after incubation to that at time 0
- SF70+73
- scaling factor calculated from CLint, in vitro, 70+73/CLH, int, in vivo for the pooled hepatocyte preparation of lot 70 and 73
- CLH, int, in vitro, 70+73
- hepatic intrinsic clearance calculated from in vitro data using the pooled hepatocyte preparation of lot 70 and 73
- CLint, in vitro, 70+73
- in vitro intrinsic clearance observed when test compounds were metabolized in the pooled hepatocyte preparation of lot 70 and 73 suspended in human serum
- FH
- hepatic availability
- CLH, predicted, 70+73
- predicted hepatic clearance from CLint, in vitro, 70+73 and average SF70+73
- QH
- hepatic blood flow rate
- RB
- blood-to-plasma concentration ratio
- DN
- dispersion number
- CLP, in vivo
- in vivo plasma clearance
- FPO, in vivo
- oral bioavailability in humans
- CLH, int, in vivo
- hepatic intrinsic clearance calculated from FPO, in vivoby the dispersion model (using the Goal Seek method attached to Microsoft Excel)
- SFmean
- mean of scaling factor calculated from CLint, in vitro, mean/CLH, int, in vivo for 10 individual lots
- average SFmean
- average value of SFmean for seven standard compounds
- FH, predicted, 70+73
- predicted hepatic availability from CLint, in vitro, 70+73 and average SF70+73
- SFbiol
- biologically based scaling factor of hepatocellularity (3.1×109 cells/kg)
- average SF70+73
- average value of SF70+73 for seven standard compounds
- Received December 13, 2001.
- Accepted April 24, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
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