Evaluation of Acute Toxicity by Means of an Exponential Model

Summary

A method of estimation of the parameters of the exponential model of acute toxicity developped earlier (J

and F , 1972; J , 1976) which in contrast to the commonly used probit method is based on a two‐parametric exponential distribution function of individual “tolerances” is presented. The parameters — the median lethal dose ( LD ₅₀ ) and the maximal generally tolerated dose ( LD ₀ ) — are estimated using the method of “modified χ ² ”. Procedures for estimation of corresponding variances and for construction of approximate 95%‐confidence limits as well as approximate tests of statistical significance for comparison of parameters estimated from different animal samples are also given. The method which possesses certain advantages over the probit method yields practically the same estimate of LD ₅₀ as shown by means of an illustratory example.