Zbinden G, Flury-Roversi M. Significance of the LD50-test for the toxicological evaluation of chemical substances. Arch Toxicol. 1981 Apr; 47(2):77-99

PMID: 7271444

Abstract

The LD50-test was developed in 1927 for the biological standardization of dangerous drugs. Then it was incorporated into the routine toxicological protocol of other classes of chemical compounds and is now part of practically all governmental guidelines which regulate toxicological testing of chemicals. For scientific, economic, and ethical reasons it is necessary to periodically reassess all toxicological test procedures, including the LD50-test. Tests which are not optimal or that have become obsolete because of new scientific knowledge, must be changed or eliminated. The review of the LD50-test shows that the precision of the procedure is dependent on the number of animals used. But even with large numbers of animals there are considerable variations of the test results, because the numerical value of the LD50 is influenced by many factors, such as animal species and strain, age and sex, diet, food deprivation prior to dosing, temperature, caging, season, experimental procedures, etc. Thus, the LD50 value cannot be regarded as a biological constant. Through standardization of the test animals and the experimental conditions the variability of the LD50 determinations can be reduced but never fully eliminated. There are several tests with which an approximate LD50 can be determined. These methods use fewer animals than the classical LD50-test, but their precision and reproducibility are sufficient for most purposes of acute toxicity testing. Through incorporation of physiological, hematological, biochemical, pathological, and histopathological investigations in the simplified test procedures with small numbers of animals, it is possible to markedly increase the informational content of the results with regard to the toxicological spectrum and the target organs of toxicity. Such studies have already replaced the LD50-test in large animals, such as dogs and monkeys. It is also desirable to replace the LD50 in rodents with such a procedure.