Toxicity studies animal numbers

A novel approach to the problem of amiaoglycoside nephrotoxicity has been to search for compounds that can inhibit toxicity without compromising efficacy. A number of agents have been reported to reduce amiaoglycoside toxicity ia animal models the most extensively studied of these is sodium polyaspartate (103—107). 

Animal studies indicate that nutritional deficiencies in a number of essential elements (e.g., calcium, iron, zinc, copper, phosphorus) may impact the toxicokinetic and toxicological behavior of lead (ATSDR 1993 Chaney et al. 1989). In infants and children, lead retention has been shown to be inversely correlated with calcium intake (Johnson and Tenuta 1979 Sorrell et al. 1977 Ziegler et al. 1978). Zinc has been shown to have a protective effect against lead toxicity in a number of animal species (Goyer 1986 Haeger-Aronsen et al. 1976 Brewer et al. 1985 Cerklewski and Forbes 1976). 

TABLE 2.8. Numbers of Animals per Dosage Group in Systemic Toxicity Studies... 

Chronic and subchronic toxicity studies are conducted to define the dose level, when given repeatedly, that cause toxicity, and the dose level that does not lead to toxic findings. In Japan, such studies are referred to as repeated-dose toxicity studies. As with single-dose studies, at least two animal species should be used, one rodent and one nonrodent (rabbit not acceptable). In rodent studies, each group should consist of at least 10 males and 10 females in nonrodent species, 3 of each sex are deemed adequate. Where interim examinations are planned, however, the numbers of animals employed should be increased accordingly. The planned route of administration in human subjects is normally explored. The duration of the study will be dictated by the planned duration of clinical use (Table 2.14). 

DePass, L., Myers, R., Weaver, E. and Weil, C. (1984). An assessment of the importance of number of dosage levels, number of animals per dosage level, sex, and method of LD50 and slope calculations in acute toxicity studies. In Acute Toxicity Testing Alternative Approaches, Vol 2 (Goldberg, A., ed.). Mary Ann Liebert, Inc. New York, pp. 139-153. 

Metabolism and pharmacokinetic studies have greater relevance when conducted in both sexes of young adult animals of the same species and strain used for other toxicity tests with the test substance. The number of animals used in metabolism and pharmacokinetic studies would be sufficient to reliably estimate population variability. This usually means a separate (but parallel) set of groups of animals in rodent studies. A single set of intravenous and oral dosing results from adult animals, when combined with some in vitro kinetic results, may provide an adequate data set for the design and interpretation of short-term, subchronic and chronic toxicity studies. 

Chronic in vivo toxicity studies are generally the most complex and expensive studies conducted by a toxicologist. Answers to a number of questions are sought in such a study, notably if a material results in a significant increase in mortality or in the incidence of tumors in those animals exposed to it. But we are also interested in the time course of these adverse effects (or risks). The classic approach to assessing these age-specific hazard rates is by the use of life tables (also called survivorship tables). 

A number of clinical chemistry parameters are commonly determined on the blood and urine collected from animals in chronic, subchronic, and occasionally, acute toxicity studies. In the past (and still, in some places), the accepted practice has been... 

These so-called subacute or subchronic toxicity studies involve the repeated application of a test substance to animals, typically for a period of 30 or 90 days. The time pattern is thus an intermediate one between acute and chronic toxicity. To test a substance for subacute or subchronic toxicity, it is mainly applied by ingestion or inhalation. Not one out of the large number of organic pigments which have thus been tested has demonstrated any irreversible toxic effect. No toxic response was observed in rats which were fed either Pigment Yellow 1 or Pigment Yellow 57 1 for 30 days [22],... 

The combined repeated dose toxicity study with the reproduction/developmental toxicity screening test (OECD TG 422, US-EPA OPPTS 870.3650) comprises a basic repeated dose toxicity study and a fertility/developmental toxicity screening test and, therefore, can be used to provide initial information on possible effects on a limited number of reproductive performance parameters. The test does not provide complete information on all aspects of reproduction, has a relatively short period of exposure, and does not provide evidence for dehnite claims of no reproductive effects, while positive results are useful for initial hazard assessment. Furthermore, results regarding repeated dose toxicity are influenced by the pregnant state of the female animals (see also Sections 4.7.3.1 and 4.7.5.2.2). 

The only real advantage of the combined study is a reduction in the number of animals required in comparison with separate fertility and embryo-fetal developmental toxicity studies. However, this is only true if male fertility is also assessed in the same investigation. If this is the case, the number of animals is reduced to approximately 100 males and 100 females compared with at least 80 males and 180 females in separate studies. If male fertility has to be assessed separately (see Subheading 1), there is no particular advantage since untreated females would also have to be procured for mating. 

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