Acute toxicity studies rodents

Test System (Animal) Several mammalian species are used for acute toxicity studies, but the rat is the preferred rodent species. The body weight variation in test animals should not exceed 20% of the mean weight. At least 10 rodents (5 females, 5 males) should be used at each dose level, and females should be nulliparous and nonpregnant. 

The EMTD is determined on the basis of a subchronic toxicity study in which small groups of test animals are exposed to a fairly broad dose range of the test substance for a period of approximately 10% of the life span of the animals (90 days for rodents). In turn, the dose levels which are tested in the 90 day subchronic study are themselves based on information generated in acute toxicity studies of the type described in the preceeding chapter. In addition to providing the EMTD the acute and subchronic tests also are utilized to obtain information on the metabolism of the test substance, the extent to which the test substance and its metabolites are distributed and bioaccumulated in the host, and which host organ systems may be affected by exposure. This information may be of importance in choosing the species or strains to be used in the chronic study as well as the route of administration. 

Acute toxicity Acute toxicity studies are required for all drugs. These studies involve administration of single doses of the agent up to the lethal level in at least two species, eg, one rodent and one nonrodent. 

The discrepancies between the ICH and MHW documents will be remedied when the latter is revised in the near future. In the meantime the situation in Japan has changed greatly since the survey was conducted. For example, some companies have only used rodents for acute toxicity studies, and all other tests were carried out in primates, the only species that expressed the relevant receptors. 

The traditional acute, subchronic, and chronic toxicity studies performed in rodents and other species also can be considered to constitute multiple endpoint screens. Although the numerically measured continuous variables (body weight, food consumption, hematology values) generally can be statistically evaluated individually by traditional means, the same concerns of loss of information present in the interrelationship of such variables apply. Generally, traditional multivariate methods are not available, efficient, sensitive, or practical (Young, 1985). 

Guzman, A., Garcia, C., and Demestre, I. Acute and subchronic toxicity studies of the new quinoline antibacterial agent irloxacin in rodents, Arzneim. Forsch., 49(5) 448-456, 1999. 

In rodent studies iron pentacarbonyl was found to have approximately one-third the acute toxicity of nickel carbonyl. At 33 ppm for 5.5 hours three of eight rats died at 18 ppm four of eight died after two 5.5-hour exposures. Multiple 5.5-hour exposures at 7ppm caused no apparent effects. 

Comprehensive toxicity studies are carried out by animal testing in order to ascertain whether the product exhibits any short-term or long-term toxicity. Acute toxicity is usually assessed by administration of a single high dose of the test drug to rodents. Both rats and mice (male and female) are usually employed. The test material is administered by two means, one of which should represent the proposed therapeutic method of administration. The animals are then monitored for 7-14 days, with all fatalities undergoing extensive post-mortem analysis. 

IPEC-Europe (intended clinical route)b ADME Acute toxicity (intended route) and skin sensitization. Ames, chromosome damage and micronucleus. Four weeks toxicity (2 species by intended route) Short-term use studies. Three-month toxicity (most appropriate species). Teratology (rat and rabbit). Genotoxicity assays Short-/midterm studies. Segment I reproduction. Six to nine months toxicity (rodent and nonrodent), segment III reproduction, and carcinogenicity (conditional)... 

FDA (intended Standard safety Acute toxicity (rodent and Short-term use studies Short-/midterm studies... 

In the evaluation of toxic characteristics of any environmental chemical, determination of oral toxicity using repeated doses may be performed after obtaining initial acute toxicity data. This provides information on possible adverse effects that may arise from repeated exposures to the test chemical over a limited period of time. Although there are major similarities in the 28-day and 14-day oral toxicity studies on rodents, the main difference lies in the time over which the dose is administered and the extent of the clinical and pathologic investigations that might be necessary for the shorter period of test. 

In addition to the rodent bioassay, the aromatic amines have been studied in the shorter term test Salmonella typhimurium mutagenicity as well as in a variety of acute toxicity assays. A number of QSARs have been generated from such data. The work of Hansch in recent years has demonstrated that the comparison of the QSAR models obtained in different systems, by putting them in a wider perspective, can provide useful clues in the study of the mechanisms of action of individual chemical classes, and can give precious hints on how appropriate the specific models and parameters selected are (Hansch, 2001 Hansch et al., 2002). An exercise of the mechanistic comparison of QSARs has been performed on aromatic amines (Benigni and Passerini, 2002). The results are detailed below. 

Acute toxicology studies in rodent and nonrodent These studies are used to identify doses causing no adverse effects and doses causing significant life-threatening effects. In addition to toxicity these studies frequently include toxicokinetics to identify the disposition of the test article in the rodent and nonrodent. These studies also provide additional support for the dose levels to be used in longer term studies. 

These segments can be tested separately or in a combined manner. All stages of development from conception to maturity and the detection of acute and delayed effects of exposure through one complete life cycle should be examined. The standard species are rodents, rats as the preferred rodent species for all study types and, the rabbit as the second nonrodent species for the embryo-toxicity studies. In some rare cases mice or monkeys are used too, if special conditions - usually kinetic data - justify such species. 

The use of a rat study for developing an RfD for GA is complicated by the fact that rodents have a much lower RBC-AChE activity level compared to humans (Ellin, 1981). By itself, this could cause rats to be relatively more sensitive than humans to anticholinesterase compounds however, the lower RBC-AChE activity may be offset by the presence of ahesterases in the blood of rats. Aliesterases, which are not found in human blood plasma, are known to bind to and, therefore, reduce the toxicity of GB, and a similar mechanism may operate in the case of GA. Other species differences, such as in the rates of aging of the GA-ChE complex, in the rates of synthesis of plasma-ChE in the liver, and in the levels of AChE in the nervous system (see Ivanov et al., 1993) may also result in difference between species in sensitivity to GA. Data are insufficient to more fuUy evaluate these possibihties. There is httle human acute toxicity data that can be compared with the available rat data however, acute toxicity data for primates in general (see Table 2) suggests that humans are likely to be more sensitive than rats. Therefore, for the purpose of this assessment, the standard EPA method will be followed which assumes that humans can be as much as ten times more sensitive to a chemical than laboratory animals. 

The conduct of animal toxicity studies proceeds concurrently with and in advance of clinical studies. A certain amount of animal toxicity data is required for the IND. This often includes acute toxicity in two rodent species, mutagenicity screening studies, and one-month toxicity studies in a rodent and non-rodent species. After the clinical studies have begun, further animal studies are conducted, usually until the time for the NDA. These would include further mutagenicity studies, reproductive toxicity studies, and long-term toxicity studies, possibly including carcinogenicity studies. 

Cocaine metabolism and disposition following acute ethanol administration were studied in the rat to determine if the in vitro effects of ethanol on cocaine methyl esterase and ethyl transferase activities had significance in vivo (Zachman et al. 1993). The rat was used as it possesses both ethyl transferase and methyl esterase activities, is frequently employed for behavioral and toxicity studies of cocaine, and the size provides sufficient tissue for anal 4 ical work. This study was designed to address three questions. First, do significant concentrations of cocaethylene form and accumulate in tissues with controlled coadministrations of cocaine and alcohol Second, does ethanol administration significantly diminish the hydrolysis of cocaine to benzoylecgonine and methanol, as occurs in vitro when cocaine and ethanol are coincubated with purified human liver carboxylesterase (Brzezinski et al. 1994 Dean et al. 1991) Third, does ethanol inhibition of cocaine methyl ester hydrolysis increase the N-oxidative metabolism of cocaine, as noted when rodents are pretreated with nonspecific esterase inhibitors (Thompson etal. 1979) ... 

V. Because pharmaceuticals are normally tested for toxicity in rodent repeated dose toxicity tests and because there is no longer a requirement for an acute high dose rodent toxicity test, the assessment of genotoxicity (e.g., bone marrow micronucleus test or other tissue/endpoint) should be integrated, if feasible, into the rodent repeated dose toxicity study to optimize animal usage. 

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