Nonrodent species

Preclinical drug development also involves animal testing [61]. Data from one rodent species and one nonrodent species are usually collected to determine the absorption, metabolism, and toxicity characteristics of the compound. Both short-term (2 weeks to 3 months) and long-term (up to several years) studies are done. The long-term studies are particularly useful for... 

Chronic Toxicity. Traditionally, chronic toxicity of new pharmaceuticals in the United States was assessed in studies of one-year duration in both the rodent and the nonrodent species of choice. The European view was that studies of six months are generally sufficient. The resulting guideline (S4A) was a compromise. Studies of six months duration were recommended for the rodent, as rodents would also be examined in two-year studies. For the nonrodent (dog, nonhuman primate, and pig) studies of nine months duration were recommended. 

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). 

Acute Toxicity Testing with Nonrodent Species... 

FIGURE 5.14. Example of pyramiding dose study for acute toxicity testing in a nonrodent species. 

In addition to rodent studies, regulatory guidelines for pharmaceuticals require that repeated dose safety studies of up to nine months (in the United States, six months elsewhere) in duration be conducted in a nonrodent species. The most commonly used nonrodent species is the dog, followed by the monkey and pig. Another nonrodent model used to a limited extent in systemic safety evaluation is the ferret. The major objectives of this chapter are (1) to discuss differences in rodent and nonrodent experimental design, (2) to examine the feasibility of using the dog, monkey, pig, and ferret in safety assessment testing, and (3) to identify the advantages and limitations associated with each species. 

Blood Collection. In rodent studies, large numbers of satellite animals (often close to the number used in the main study phase) are usually needed for pharmacokinetic blood sampling, whereas with most nonrodent species, blood samples can be collected from the main study animals without compromising their health status. 

Handling of Animals. Once rodents are acclimated to handling, they are generally relatively easy to work with. In contrast, some nonrodent species, such as nonhuman primates, are often difficult to handle because of their size, strength, emotionality,... 

Common Study Protocols. The dog is the most commonly used nonrodent species in safety assessment testing (i.e., acute, subchronic, and chronic studies). The exception to this is its use in developmental toxicity and reproductive studies. For developmental toxicity studies, the dog does not appear to be as sensitive an indicator of teratogens as other nonrodent species such as the monkey (Earl et al., 1973) or the ferret (Gulamhusein et al., 1980), and, for reproductive studies, the dog is not the species of choice because fertility testing is difficult to conduct (due to prolonged anestrus and the unpredictability of the onset of proestrus) and there is no reliable procedure for induction of estrus or ovulation. 

Greater test compound requirements than smaller nonrodent species Availability... 

Nonhuman primates are often the nonrodent species of choice for safety assessment studies. There are over 500 species of nonhuman primates that differ widely from each other in size and physical characteristics. Most of the monkeys used in experimental research belong to the suborder Anthropoidea and especially to the superfamilies of Ceboidea (marmoset, squirrel monkey) and Cercopitcoidea (macaque, papio species, rhesus). These have been popular because of (1) assumed better concordance of effects seen to those in man and (2) smaller weights (and therefore reduced compound requirement). However, predominant factors leading to a decision whether or not to select primates as the nonrodent species for safety evaluation are summarized as follows (Hobson, 2000). 

Less test material needed than for other nonrodent species Physiological, behavioral, and often, metabolic similarities to man... 

While there are advantages and disadvantages associated with all three nonrodent species, the dog is probably the nonrodent species most frequently used in safety assessment studies. This is because dogs are relatively docile and even tempered,... 

Study Type. Metabolic and pharmacokinetic data from a rodent species and a nonrodent species (usually the dog) used for repeat dose safety assessments (14 days, 28 days, 90 days or six months) are recommended. If a dose dependency is observed in metabolic and pharmacokinetic or toxicity studies with one species, the same range of doses should be used in metabolic and pharmacokinetic studies with other species. If human metabolism and pharmacokinetic data also are available, this information should be used to help select test species for the full range of toxicity tests, and may help to justify using data from a particular species as a human surrogate in safety assessment and risk assessment. 

It is recommended that testing be performed in the most relevant species, and that laboratory species and strains which are commonly used in prenatal developmental toxicity testing be employed. The preferred rodent species is the rat and the preferred nonrodent species is the rabbit. Justification should be provided if another species is used (4). 

The combined fertility and embryo-fetal development study is described as a two study design in the ICH S5(R2) guideline (1) and is anticipated for use in rodents (usually rat but also the mouse) embryo-fetal development must still be evaluated in a second, nonrodent, species. 

For many years, tJie species that have been used for teratology studies have been mainly mice, rats and rabbits. These species have satisfied investigators and regulators in the past, with most studies performed in the rat and rabbit (as the preferred rodent and nonrodent species, respectively). However, there have been a relatively large number of cases when both rodents and/or rabbits are unsuitable for running teratology smdies, often because the metabolites in the animals are not relevant to those in humans. 

Developmental Toxicity. No data are available on the developmental toxicity of 2,3-benzofuran in humans or animals. Thus, a complete investigation of the effects of 2,3-benzofuran on development, studying one rodent and one nonrodent species exposed by all three routes, would be useful to evaluate potential developmental toxicity in humans. 

Chronic toxicity Rodent and nonrodent species for > 6 months. Required when drug is intended to be used in humans for prolonged periods. Usually run concurrently with clinical trials. Determine same end points as subacute toxicity tests. 

Three-month toxicity (rodent and nonrodent species by appropriate route). Parenteral use studies (conditional)... 

ICH 4.1.3 Assessment of Developmental Toxicity. This is almost identical to the segment II study protocol. Pregnant animals are exposed from implantation through organogenesis. The parameters measured in the segment II study are similar. However, the study is usually conducted using at least two species. More specifically, at least one rodent and one nonrodent species. 

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