In vivo animal data

Because DMPK properties vary among different species, in vitro human and animal data and in vivo animal data cannot always be extrapolated to human in vivo responses. The three main reasons that drugs fail during clinical trials are (1) lack of efficacy, (2) unacceptable adverse effects, and (3) unfavorable ADME properties. Hence, clinical development is necessary to establish solid experiment-based human exposure and safety data through both short- and long-term monitoring. 

In which the terms Ha refers to the number of free electron pairs, MW is the molecular weight, and clogP is the computed lipophilicity. While this method could be stated to be "partially in silico" because it utilizes some chemical descriptors, the need for in vivo animal data and their dominance in the individual terms really makes this approach more of an animal-human correlation than an in silico method. Finally, in the same report, the authors describe a regression based solely in animal data. Overall, the performance of these... 

Figure 12 In vitro permeation through human skin and in vivo animal data after dermal application of fentanyl MDTS. (a) Absorption of fentanyl across human epidermis. Comparison of a fentanyl MDTS and Duragesic 50 TS. (b) Mean plasma concentration of fentanyl after a fentanyl MDTS and Duragesic 50 TS in male pigs (n = 7).

The landscape of pharmaceutical research has changed. There is increased pressure to discover medicines and to get those medicines into patient populations as quickly and inexpensively as possible. This pressure drives efforts to predict ADME properties in humans with human in vitro metabolism data, and correlations between in vitro and in vivo animal data. These same factors, speed and cost, also fuel research to use in vitro data alone to predict in vivo ADME properties in animals. While the exclusive use of in vitro data would... 

Genotoxicity. Data on the genotoxicity of ammonia in humans are limited to a study of workers at a fertilizer factory that found an increase in clastogenic effects (Yadav and Kaushik 1997). In vivo animal data consist of a study in mice that found alterations in the occurrence of micronuclei (Yadav and Kaushik 1997) and several studies in Drosophila melanogaster that resulted in a positive response for mutagenic lethality (Lobasov and Smirnov 1934), but negative responses for sex-linked recessive lethal... 

Genotoxicity. Studies of miners and other populations exposed to radon and radon daughters showed an increased occurrence of chromosomal abnormalities. However, because exposure-effect relationships have not yet been established and the biological significance of these chromosomal effects is uncertain, further studies should be performed. In vitro studies using human cell lines could help determine a dose-response for exposure to radon and radon daughters and increased chromosomal abnormalities. Such relationships may be difficult to establish because of possible interactions with other substances, i.e., uranium ore dust. There are no in vivo animal data to support the observed increase in chromosomal abnormalities in human populations. Further observations in laboratory animals are needed to explain these effects. 

A significant proportion of the research on flavonoids has concentrated on their antioxidant actions, and their capacity to act as antioxidants remains their best described biological property to date. Their antioxidant ability is well established in vitro, and in vivo animal data also suggest that consumption of compounds such as rutin or red wine extracts, tea, or fruit juice lowers oxidative products such as protein carbonyls, DNA damage markers, and malonaldehyde levels in blood and a range of tissues. 

Data on safety have been obtained from in vitro as well as in vivo animal and human studies (see also Section 10.4). About 50 years ago, Australian farmers observed an infertility syndrome in sheep associated with the consumption of clover species (Bennets et al., 1946). The clover compounds shown to cause the infertility (genistein, daidzein, equol, biochanin A, formononetin) were members of the isoflavone family (Bradbury and White, 1951 Shutt and Braden, 1968), raising the question of whether soy might cause infertility in humans (see also Section 10.4.9). A variety of reports further supported adverse effects of isoflavones on animal reproductive systems (Santell et al., 1997 Flynn et al., 2000a,b). 

Rules and filters do exceptions exist Off course they do. Common sense is required. There is a natural priority order in drug discovery decision making. Clinical information trumps all. Next in importance is high quality experimental evidence, e.g., in vivo animal experiments. Rules and filters come into play when clinical and experimental data is lacking. 

A lead is variously defined in the pharmaceutical industry as a compound derived from a hit with some degree of in vitro optimization (potency in primary assay, activity in functional and/or cellular assay), optimization of physical properties (solubility, permeability), and optimization of in vitro ADME properties (microsomal stability, CYP inhibition). Moreover, a lead must have established SAR/SPR around these parameters such that continued optimization appears possible. A lead may also have preliminary PK and in vivo animal model data. However, it is the task of the lead optimization chemist to improve PK and in vivo activity to the levels needed for identification of a clinical candidate. 

Obach et al. [27] proposed a model to predict human bioavailability from a retrospective study of in vitro metabolism and in vivo animal pharmacokinetic (PK) data. While their model yielded acceptable predictions (within a factor of 2) for an expansive group of compounds, it relied extensively on in vivo animal PK data for interspecies scaling in order to estimate human PK parameters. Animal data are more time-consuming and costly to obtain than are permeability and metabolic clearance data hence, this approach may be limited to the later stages of discovery support when the numbers of compounds being evaluated are fewer. 

The guideline acknowledges that there could be very unusual cases in which the thorough QT/QTc study is negative but the available nonclinical data are strongly positive (e.g. hERG positive at low concentrations and in vivo animal model results... 

The degree of exposure of the fetus to a particular substance can be best assessed in human subjects, but concerns of fetal safety have restricted the use of this approach. Moreover, clinical studies cannot elucidate the various mechanisms that contribute to transplacental transport of a particular compound. There are many structural differences between the human placenta and the placenta of other mammalian species, which complicates extrapolation of data obtained from in vivo animal models to humans [7], Thus, several ex vivo and in vitro techniques have been developed to study the placental role in drug transfer and metabolism during pregnancy and there are some excellent articles that discuss these systems in detail [7], Both isolated tissues and various cell culture techniques are currently in use and these have been summarized below. 

The preliminary models can be used to select compounds for synthesis and to determine which data is most important to generate to understand the PK properties of a particular compound or series. As compounds are generated and at first low-throughput and then high-throughput data become available, the model can be updated and when possible validated against in vivo PK data in animals. Mismatches between model predictions and data indicate missing mechanisms or inadequate data. If the model prediction does not match the data, the model can be used to develop... 

Therefore in practice, normally, animal toxicity data is required (see above). Of course, the differences between humans and other species must always be recognized and taken into account (see below). It may be possible to use in vitro data both from human cells and tissues as well as those from other animals to supplement the epidemiological and animal in vivo toxicity data. However, at present such data cannot replace experimental animal or human epidemiological data. The predictive use of structure-activity relationships is also possible, and it is an approach, which is becoming increasingly important. 

We had sought to address two questions (a) what is the elimination half-life of DS-96 in the murine model, and does the tV2 correspond to pharmacodynamic data shown in Fig. 12.19 (b) what is the therapeutic plasma concentration of DS-96 that corresponds to full protection against endotoxemic challenge in mice. DS-96 at a dose of 200 (xg/mouse (8 mg/kg) was administered to CF1 mice via i.p. and i.v. routes. Plasma concentrations of DS-96 were determined by LC-MS/MS using a deuterated DS-96 internal standard (Nguyen et al., 2008 Shrestha et al., 2008). The elimination tV2 in mice is about 400 min (Fig. 12.22), which is consistent with the observed pharmacodynamic (in vivo efficacy) data shown in Fig. 12.19. The observed concentration-versus-time profile of DS-96 in the mouse i.p. model suggests that a plasma concentration of 0.5-1.5 txg/mL corresponds to complete protection by a dose of 200 ng/animal of LPS in the D-galactosamine-primed model of endotoxin-induced lethality. 

This chapter provides an overview of factors affecting dermal absorption. Factors influencing absorption are among others related to the skin (e.g. anatomical site, difference between species, metabolism, etc.) and the exposure conditions (e.g. area dose, vehicle, occlusion and exposure duration). In order to provide relevant information for the risk assessment of pesticides, dermal absorption studies should take these aspects into account. With respect to the methods being used nowadays for the assessment of dermal absorption, it is important to realize that neither in vitro nor in vivo animal studies have been formally validated. Available data from various in vitro studies, however, indicate that the use of the total absorbed dose (i.e. the amount of test substance in the receptor medium plus amount in the skin) could be used in a quantitative manner in risk assessment. Tape stripping of the skin can be adequate to give a good indication of test chemical distribution, and hence its immediate bioavailability. 

Elaboration of toxicokinetic data of chemical warfare agents is essential for designing effective antidotes, improving first aid, and optimizing therapeutic regimen and medical care. It has to be eonsidered that data obtained from in vitro or in vivo animal studies need earefiil extrapolation to humans whieh, at least, requires sophisticated mathematical models to eonsider basie interspecies differenees (Langenberg et ah, 1997 Levy et ah, 2007 Sweeney et al, 2006 Worek et al, 2007). 

Development and validation of in vitro and/or in vivo animal models for rapid screening of molecular hbraries to identify potential medical countermeasures is another priority of the CounterACT program. These models include seizures in small mammals, models of direct lung injury from an inhaled source, animal models of cyanide intoxication, and medium throughput models of dermal or ocular injuries. It is important that models be amenable to use under GLP methodology so that the data generated are acceptable to the FDA. Since adherence to GLP standards may be expensive, earher screens to identify potential hits are usually performed under non-GLP conditions. 

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