THE INHALATION ACUTE TOXIC CLASS METHOD - TEST PROCEDURES AND BIOMETRIC EVALUATIONS

A method of inhalation acute toxic (ATC) classification is presented w ith the use of significantly fewer animals in comparison with the clas sical LC50 test. The principle of the inhalation ATC method is based o n the oral ATC method, which has been adopted in 1996 as an official t est guideline of the OECD and the European Union. The inhalation ATC m ethod, like the oral ATC method, is a stepwise procedure; three animal s of each sex are used simultaneously for each tested concentration, a nd not, as in the oral ATC method, three animals of each sex separatel y for each dose. The method was developed for three starting concentra tions and two reference systems (based on ppm and mg/l). Depending on the LC50, slope, classification system and starting concentration, on average 50 to 80% fewer animals will be used in comparison to at least 30 animals with the classical LC50 test. The method was biometrically evaluated with the use of the probit model for dose-response relation ships. At present, there are 12 different international classification systems based on LC50 values: 6 systems referring to mg/litre and 6 s ystems based on ppm values, and exposure time varying from 1 to 4 h. T he test procedures and the calculations of the classification probabil ities demonstrate that the inhalation ATC method is a reliable alterna tive to the classical LC50 test with the use of significantly fewer an imals. Classification probabilities are presented for all classificati on systems currently in use, and expected numbers of experimental and of moribund/dead animals are demonstrated for one system of each refer ence system and for all three starting concentrations. The conclusion is justified that there is no need to validate the inhalation ATC meth od with the use of experimental animals.