A Practical Approach, Second Edition=Ronald D. Ho.pdf

220 DEVELOPMENTAL REPRODUCTIVE TOXICOLOGY: A PRACTICAL APPROACH, SECOND EDITION• The number of mated females per group• The number of days (and gestational days) of treatment• The dose levels in mg/kg/day (as assigned), mg/ml (as formulated), ppm, dietary percentage, andin mg/m 3 , etc.• The dosing volume in ml/kg, if appropriate• Projected in-life study performance dates should also be documented as follows:– Animals arrive at performing laboratory– Dates of GD 0 (for rodents, the end date is tentative since it will depend on performance ofthe breeding pairs)– Inclusive dates of treatment (the end date will depend on GD 0 dates)– Dates of scheduled sacrifice (the end date will depend on GD 0 dates)The date of anticipated submission of the draft report may also be included in this section (or underthe section on reports).B. Dose SelectionAll current governmental testing guidelines call for at least three dose or concentration levels plusa concurrent vehicle control (four groups total). The top dose level should be chosen to result indemonstrable maternal (and possibly developmental) toxicity. Maternal indicators can includereductions in body weight or weight gain, treatment-related clinical signs of toxicity, sustainedreductions in food and/or water consumption, and maternal mortality (not to exceed 10%). 41,42 Themiddle dose should result in minimal maternal (and possible developmental) toxicity. The low doseshould be a NOAEL (No Observable Adverse Effect Level) for both maternal and developmentaltoxicity. Optimally, the selection of doses should be based on results of range-finding studies inpregnant animals. A distant second choice on which to base doses would be a 14-day repeated dosestudy in the same species and strain by the same route in the same sex (although the animals werenot pregnant, and pregnancy changes many physiologic and toxicologic parameters). Informationon absorption, distribution, metabolism, and excretion in the test species (and sex) would be veryuseful, but it is rarely available for commercial chemicals and pesticides (most likely available fornew drug preclinical work) and is almost never available for pregnant females. The spacing of thedoses may be arithmetic or logarithmic; the low dose should be selected, if possible, to allowapplication of safety factors during risk assessment and still be above any expected human exposurelevels. The doses selected and their justification should be documented in this section.C. Allocation and Treatment of Mated Females1. AllocationThe number of females assigned to dose groups is defined by the protocol. Animals can be assignedto dose groups totally randomly (by computer, by a table of random numbers, by numbered cardsdealt randomly, etc.), or they can be assigned on the basis of body weight (i.e., stratified by bodyweight but randomly within body weight classes).For mated females to be assigned to study by stratified randomization, GD 0 weights arearranged in ascending order, from the lightest to the heaviest on the first GD 0 date, and assignedin the same order or reverse order (i.e., descending order from heaviest to lightest) on subsequentdays. Beginning with the lightest weight, animals are assigned to groups stratified by body weight(number of animals per group equals number of treatment groups). Within each stratified group,one animal will be randomly assigned to each treatment group. In the event that the total numberof animals inseminated on a given day is not an even multiple of the number of treatment groups,the stratified group with the heaviest body weights (the last group filled by stratified randomization)will be assigned randomly (one animal per treatment group) until all animals have been assigned.© 2006 by Taylor & Francis Group, LLC