Highest dose selection

Highest Dose Selection It is sometimes difficult to set the highest dose for safety programs of a biopharmaceutical when low or no toxicity is observed in animals. The JPMA questionnaire survey revealed that most pharmaceutical... 

The EPA and PDA state that there is no standard treatment schedule therefore, one, two, or more doses every 24 h is acceptable as long as toxicity has been demonstrated, or that a limit dose has been achieved. In addition, if a large volume of material needs to be administered to the rodents, it may be administered as a divided dose, as long as the doses are not separated by more than a few hours. Doses may be selected from the results of a range finding study, or any preliminary tests done with the rodents after administration via the same route. The highest dose selected for the main assay would produce some bone marrow toxicity, including, in the bone marrow or peripheral blood, a decreased number of immature erythrocytes to total erythrocytes. In the case of a nontoxic test article, the limit dose is defined as 2000 mg kg... 

The results of these studies showed a remarkable similarity in the effects produced by the selective DPP-8 inhibitor and a//o-isoleucyl thiazolidide [21]. Both compounds produced mortality and alopecia at the highest doses tested, and both also produced thrombocytopenia of similar magnitude at doses >30mpk, and enlarged spleens and lymph nodes at all doses tested. The QPP selective inhibitor produced significant reductions in reticulocyte counts at the 100 mpk dose. No other changes were noted. In contrast to the above compounds,... 

For most pharmaceutical companies, the doses selected are as follows. The highest dose is selected to be the estimated maximum tolerated dose (MTD). The lowest dose is usually a small multiple (1 to 5 times) of the MRHD, and the middose approximates the geometric mean of the other two doses (PMA, 1988 McGregor, 2000). 

Some sophisticated guessing goes into dose selection. Knowledge of the minimum acutely toxic dose helps the toxicologist pick the highest dose to be used it will be somewhere below the minimum lethal dose. There is usually little basis for deciding the lowest dose it is often set at some small fraction of the high dose. Whether it turns out to be a NOAEL will not be known until the experiment is completed. Sometimes bioassays have to be repeated to identify the NOAEL. 

Pregnant mice exposed to 40, 200, or 1000 ppm 1,3 butadiene 6 hours/day on gestational days 6-15 had maternal toxicity at the two highest dose groups significant exposure-related reductions in the mean body weights of male fetuses occurred at 40 ppm and higher. There was no evidence of selective developmental toxicity in rats similarly exposed, and no increased incidence of malformations was observed in either study. " ... 

One rodent species (preferably rat) should be used. Dose selection should be based on the results of the previous 14- or 28-day toxicity study in rat. Three dose groups, the highest one showing minimal toxicity in systemic studies, and a control group should be included. Each group should consist of six adult male animals. Animals should be treated with the test substance by the intended route of clinical use for minimum 28 days and maximum 70 days before they are paired with female animals of proven fertility in a ratio of 1 2 for mating. 

The dose levels would be selected from existing toxicological data. Unless otherwise indicated, the dose levels used in a previous general toxicity study in the same species will serve as a guide. The main purpose is to select an appropriate highest dose level for the main study it is not possible to positively determine a no-effect level in a preliminary study. 

The test can be carried out on cultured cells or on cells from animals treated in vivo. In the former case the test chemical is usually evaluated in the presence and absence of the S-9 activation system from rat liver. Typically cells from a Chinese hamster ovary cell line are incubated in a liquid medium and exposed to several concentration of the test chemical, either with or without the S-9 fraction, for about 2 hours. Positive controls, such as ethyl methane sulfonate (a direct-acting compound) or dimethylni-trosamine (one that requires activation), as well as negative controls are also included. Test concentrations are based on cell toxicity levels determined by prior experiment and are selected in such a way that even at the highest dose excess growth does not occur. At the end of the treatment period the cells are washed, bromodeoxyuridine is added, and the cells are incubated for 24 hours or more. The cells are then fixed, stained with a fluorescent dye, and irradiated with UV light. Second division cells are scored under the microscope for SCEs (Figure 21.7). 

Other considerations can influence the selection of the highest dose level. Rats and mice are relatively insensitive to sulfo-ureas used for the treatment of diabetes. Rats counteract the hypoglycaemic effect of these drags by secretion of glucagon and 25-hydroxy-cortisol and no hypoglycaemia occurs at the maximum dose level (> 5 000 mg/kg). In one case of a novel antidiabetic sulfonylurea it was demonstrated that absorption becomes saturated at relatively low oral dose (ca. 1000 mg/kg). This observation convinced the FDA that testing of the maximum tolerated dose (probably not determinable) is not necessary. By that the demand of test material could be reduced at least by a factor of 5. 

Subacute or subchronic assays assess the effects of daily exposures of an animal population to a toxicant over approximately 10% of the animal s lifetime. In rats, this corresponds to about 3 months. Careful study of the animals—including examination of all body tissues and fluids—reveals the dose at which toxic effects begin to occur at several endpoints, such as organ dysfunction, behavioral changes, or alterations in levels of normal body fluid components. The highest dose at which none of the animals show toxic effects is called NOAEL (i.e., no observable adverse effect). Other doses include LOEL (lowest observed effect level), the lowest dose for which effects were expressed and LOAEL (lowest observed adverse effect level), a stricter version of LOEL that addresses only adverse effects. In these tests several species are tested and the most sensitive one is selected as a human surrogate. See Figure 9.32. 

If a NOAEL is selected or derived as the endpoint for an AEGL severity level of concern, identifying both the highest dose at which the effect is not seen and the lowest dose at which it is seen for each AEGL severity level strengthens the confidence in the study. 

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