No abstract

ABSTRACT:The disposition of atorvastatin, cerivastatin, and indomethacin, established substrates of rat hepatic basolateral uptake transporters, has been evaluated in suspended rat hepatocytes. Cell and media concentration-time data were simultaneously fitted to a model incorporating active uptake, permeation, binding, and metabolism. Use of the model to estimate the ratio of intracellular to extracellular steadystate free drug concentrations demonstrated the strong influence of active uptake on the kinetics of atorvastatin (18:1) and cerivastatin Isolated hepatocytes are an important in vitro system for studying the disposition of drugs, reflecting both the key role of the liver in the elimination of foreign compounds and also the ability of isolation and maintenance procedures to retain the integrity of many functional hepatic components (Li et al., 1999;Soars et al., 2007). Pharmacokinetic models can be applied to study the movement of molecules in and out of cells and to quantify their intracellular binding and metabolism. This approach has been used extensively to study the kinetics of compounds within the whole organ (Goresky and Schwab, 1988;Sirianni and Pang, 1997;Liu and Pang, 2005) but can also be applied to derive a greater understanding of the behavior of drugs in isolated hepatocytes, thereby exploiting this model system.Hepatocyte intrinsic metabolic clearance (CL int,met ) can be obtained from in vitro metabolism experiments by sampling a homogeneous hepatocyte suspension over time and either dividing the rate of metabolite formation by the initial substrate concentration (Houston et al., 2003) or by estimating the depletion rate of parent compound; for both methods, a correction is made to the clearance from the incubation (CL inc ) for the fraction unbound in the incubation (fu inc ). This latter approach has been used widely in the industry for the last 5 to 10 years Houston, 2004, 2005;McGinnity et al., 2004;Riley et al., 2005;Soars et al., 2007) and is referred to as the "standard method" in the manuscript. For many highly permeable drugs, where the intracellular concentration of free drug can be assumed to be equal to that in the plasma, relatively simple liver models can be used to estimate intrinsic metabolic clearance in the liver (CL int,L ) from in vitro data (Houston and Carlile, 1997;Lau et al., 2002;McGinnity et al., 2004). CL int,L can also be estimated from in vivo data by correcting plasma concentration-time data for plasma protein binding (Houston, 1994).However, where the intracellular concentration of free drug is likely to be significantly different to that in the media (for example, diffusion-limited or uptake transporter protein mediated kinetics), more Article, publication date, and citation information can be found at http://dmd.aspetjournals.org. doi:10.1124/dmd.107.019455.□ S The online version of this article (available at http://dmd.aspetjournals.org) contains supplemental material.ABBREVIATIONS: CL int,met , unbound metabolic intrinsic clearance; CL inc , clearance f...

We present herein a QSAR tool enabling an entirely in silico prediction of human and rat steady-state volume of distribution (Vss), to be made prior to chemical synthesis, preceding detailed allometric or mechanistic assessment of Vss. Three different statistical methodologies, Bayesian neural networks (BNN), classification and regression trees (CART), and partial least squares (PLS) were employed to model human (N=199) and rat (N=2086) data sets. The results in prediction of an independent test set show the human model has an r2 of 0.60 and an rms error in prediction of 0.48. The corresponding rat model has an r2 of 0.53 and an rms error in prediction of 0.37, indicating both models could be very useful in the early stages of the drug discovery process. This is the first reported entirely in silico approach to the prediction of rat and human steady-state volume of distribution.

ABSTRACT:Identifying any extrahepatic excretion phenomenon in preclinical species is crucial for an accurate prediction of the pharmacokinetics in man. This understanding is particularly key for drugs with a small volume of distribution, because they require an especially low total clearance to be suitable for a once-a-day dosing regimen in man. In this study, three animal scaling techniques were applied for the prediction of the human renal clearance of 36 diverse drugs that show active secretion or net reabsorption: 1) direct correlations between renal clearance in man and each of the two main preclinical species (rat and dog); 2) simple allometry; and 3) Mahmood's renal clearance scaling method. The results show clearly that the predictions to man for the methods are improved significantly when corrections are made for species differences in plasma protein binding. Overall, the most accurate predictions were obtained by using a direct correlation with the dog renal clearance after correcting for differences in plasma protein binding and kidney blood flow (r 2 ‫؍‬ 0.84), where predictions, on average, were within 2-fold of the observed renal clearance values in human.