In vitro data

In recent years, several types of in vitro approaches have been developed to assess the absorption and metabolic pathways of substances. Except for the OECD TG 428, Skin Absorption In Vitro Method, none of these test methods have yet been adopted as a test guideline method. 

Ex vivo systems derived from animals and from human organs can be used to investigate the in vitro metabolism of xenobiotics. Cell lines, which are transfected to express species-specific metabolic enzymes, can also be used to identify the enzymes involved in the metabolism of a specific substance. Blocking the metabolism by an enzyme specific substrate or by antibodies is also helpful for the identification of the enzymes involved in the metabolism of a substance. 

Toxicological Risk Assessments of Chemicals A Practical Guide 

The in vitro approaches may give qualitative and under special circumstances, also, quantitative information. Information from in vitro experiments, in particular data on in vitro metabolism, has been used in PBTK models (Section 4.3.6). The use of data derived from in vitro test systems should be very carefully considered in the risk assessment until such approaches have been appropriately validated. 

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Cefpimizole (51) appears to be less active in vitro than cefotaxime and cefoperazone and to have a somewhat narrower activity spectrum although some strains of Pseudomonas are susceptible. It is not orally active, but its performance in vivo appears superior to what would be expected from its in vitro data. Its synthesis begins by acylation of cephaloglycin (48) with the bis acid chloride of imidazole-4,5-dicarboxylic acid (49) to give amide 50. The acetyl moiety at C-3 of this intermediate is displaced with 4-pyridineethanesulfonic acid and sodium iodide to give cef-pimazole (51) [16]. 

In the case of dmg interactions involving metabolic inhibition, little increase in the substrate concentration is expected when the inhibition constant (K ) determined in in vitro studies using human liver samples is larger than the inhibitor concentration in vivo. Various approaches have been adopted using mathematical models in attempts to quantitatively predict in vivo dmg interactions from in vitro data [5]. 

The chapter covers end points in the same order they appear within the Discussion of Health Effects by Route of Exposure section, by route (inhalation, oral, dermal) and within route by effect. Human data are presented first, then animal data. Both are organized by duration (acute, intermediate, chronic). In vitro data and data from parenteral routes (intramuscular, intravenous, subcutaneous, etc.) are also considered in this chapter. If data are located in the scientific literature, a table of genotoxicity information is included. 

Various antimalarial drugs have been studied in biodegradable delivery systems. Wise (89) reported the use of a lactide/glycolide copolymer and also poly(L-lactic acid) for release of drugs such as quinazoline and sulfadiazine. Although in vitro data and experiments in mice were somewhat encouraging, these early formulations failed to reach significant clinical status. 

The in vitro measurements of permeability by the cultured-cell or PAMPA model underestimate true membrane permeability, because of the UWL, which ranges in thickness from 1500 to 2500 pm. The corresponding in vivo value is 30-100 pm in the GIT and nil in the BBB (Table 7.22). The consequence of this is that highly permeable molecules are (aqueous) diffusion limited in the in vitro assays, whereas the membrane-limited permeation is operative in the in vivo case. Correcting the in vitro data for the UWL effect is important for both GIT and BBB absorption modeling. 

Grass, G. M., Simulation models to predict oral drug absorption from in vitro data, Adv. Drug. Del. Rev. 23, 199-219 (1997). 

As noted earlier, osmotic systems have been shown to provide good in vitro-in vivo correlations between the observed release rates. This has been shown explicitly for the core I devices described above [33], The data are shown in Figure 16, where the in vitro data are plotted along with the release curves from six devices administered to dogs. The animals were in the fed state at the time of administration and maintained that way throughout the duration of the experiment via the administration of —50 g of dog chow before device administration and every hour thereafter. The individual release curves shown in Figure 16 were obtained by numerical deconvolution of the plasma data with an oral solution dose given to the same dog. Clearly the in vivo and in vitro data are... 

In assessing animal data, careful attention must be paid to the quality of the data, the incidence of spontaneous tumors in the control population, consistency if more than one study is available, and statistical validity. If the exposure route and experimental regimen employed do not agree with the most likely mode(s) of human exposure (e.g., intramuscular injection), the data must be interpreted cautiously. Consideration should be given to data on metabolism of the compound by the animal species tested, as compared with metabolism in humans if this information is known. If only in vitro data are available, only qualitative estimates may be possible because of uncertainties regarding the association between in vitro results and human or animal effects. The availability of associated pharmacokinetic data, however, may allow development of a rough quantitative estimate. 

QSAR models with a regulatory purpose should mimic the in vivo (and occasionally, in vitro) data, which are typically used in the context identified by the law. As a consequence it should be very much preferable that also the data on the basis of the QSAR models are experimental data suitable for the regulation. In any case, their quality should be very high, and a check should be done on it. 

EEG slow waves. The differential EEG and ACh responses to dialysis delivery of AF-DX 116 (M2/M4) versus pirenzepine (M1/M4) supports the conclusion that, in B6 mouse, postsynaptic muscarinic receptors of the Ml subtype form one receptor mechanism by which ACh activates the EEG (Douglas et al, 2002a). The data summarized in Fig. 5.11 provide direct measures of G protein activation in basal forebrain and prefrontal cortex by muscarinic cholinergic receptors (DeMarco et al, 2004). The in vitro data of Fig. 5.11A indicate the presence of functional muscarinic receptors in regions of B6 mouse prefrontal cortex where in vivo microdialysis studies (Douglas et al, 2002a, b) revealed modulation of ACh release and EEG by pre- and postsynaptic muscarinic receptors (Figs. 5.9 and 5.10). 

Quantitative Prediction of in vivo Disposition from in vitro Data... 

Ueda, K., Kato, Y., Komatsu, K., Sugiyama, Y., Inhibition of biliary excretion of methotrexate by probenecid in rats quantitative prediction of interaction from in vitro data, J. Pharmacol. Exp. Ther. 2001,... 

In spite of its limitations, the ACAT model combined with modeling of saturable processes has become a powerful tool in the study of oral absorption and pharmacokinetics. To our knowledge, it is the only tool that can translate in vitro data from early drug discovery experiments all the way to plasma concentration profiles and nonlinear dose-relationship predictions. As more experimental data become available, we believe that the model will become more comprehensive and its predictive capabilities will be further enhanced. 

This model integrates existing in vitro data, such as Caco-2 permeability (Papp) and metabolic stability in liver S9 or microsomes, to estimate bioavailability as being either low, medium, or high. Oral bioavailability predictions for not only humans but also other species can be made by using the metabolic stability values of drugs in liver microsomal enzyme preparations from that species. A premise of this model is that metabolic clearance is more important than renal or biliary clearance in determining bioavailability. However, despite the lack of in vitro renal... 

This model uses in vitro data to estimate the oral bioavailability ranges of chemically diverse compounds in a range of species, and represents a potentially powerful tool when combined with high-throughput in vitro screening. 

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