Since there are no reliable non-animal methods for determining the acute toxicity of chemicals/drugs to mammals, such information must be obtained from animal studies. The rationale and specific justification for the study must be presented to the Institutional Animal Care and Use Committee (IACUC) in the Animal Study Protocol Application Form, along with Appendix IV (Radioisotopes/Toxic Chemicals/Biological Hazards). If novel or unknown compounds are being used, Appendix VII must also be completed. The procedure must be designed to minimize the number of animals used and the duration and extent of distress, if any, experienced by treating animals. The protocol must be presented to the IACUC and approved before the testing begins.
Three basic approaches are commonly used to develop information of this nature for compounds of unknown potency: (1) A “limit” test is suitable to determine if the test compound is or is not toxic or lethal at a predetermined dose level (usually, a single large dose). Normally, 1 or 2 animals are exposed initially and if toxicity is not observed, additional animals may receive the same dose to confirm its “safety;” (2) Range finding tests generally utilize 1 or 2 animals per dose level over a range of doses that will permit estimation of an approximate LD50; (3) In those cases in which an LD50 test is necessary, it may be determined by using 3-5 dose levels with 5-10 animals/dose; the middle dose should approximate the LD50. If lethality of the compound is unknown, the range finding test should be conducted first to establish appropriate dose levels in order to minimize the number of animals used.
In all of these tests, animals must be observed closely for at least one hour following dosing for signs of pain or distress. If pain or distress is produced that had not been anticipated, and thus not evaluated by the IACUC, the Attending Veterinarian must be informed immediately. Continuation of testing may require modification of the protocol and a reevaluation by the IACUC.
When possible, the test agent should be well characterized as to its composition and purity prior to animal exposure. Following dosing, animals should be kept for observation over a period of time consistent with the objectives of the study. Most standard acute toxicity tests require at least 14 days, and some longer, to detect delayed signs of toxicity. Moribund animals should be sacrificed as soon as feasible, particularly if pain or discomfort is evident.
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