Comparison of two in vitro and two in vivo methods for the measurement of irritancy

A number of in vitro assays have recently been developed that need further validation in order to judge their value for local tolerance testing. For this purpose, results from the following experiments were compared: (A) cytotoxicity testing in cell culture (neutral red assay); (B) tests with the chorioallantoic membrane of fertilized chicken eggs; (C) rabbit eye mucous membrane tests; and (D) occluded epicutaneous testing in human volunteers. The data presented indicate that in vitro testing with the first two methods yields reliable results with respect to the eye and human skin irritation data within homologous substance classes. A test procedure is proposed that involves comparative testing of the chemicals with unknown irritant properties together with known weak and strong irritants from the same class of chemicals as standards in the test series. This procedure seems to be suitable as a preliminary screen for identifying severe irritants prior to the performance of any in vivo studies. It would reduce the number of animals to be used in vivo and lead to the avoidance of exposure of animals to harmful substances.