Using In Vitro Data to Estimate In Vivo Starting Doses for Acute Toxicity 4.0 RECOMMENDED BASAL CYTOTOXICITY TESTS: BALB/C 3T3 AND NORMAL HUMAN KERATINOCYTE (NHK) NEUTRAL RED UPTAKE (NRU) TESTS 4.1 Validation Status of the 3T3 NRU Test

The BALB/c 3T3 NRU test is probably the cytotoxicity test that has been used most frequently in formal validation programs, all of which were aimed at evaluation of cytotoxicity in predicting eye irritancy. Large-scale studies to be mentioned here are Phases I, II, and III of the Cosmetic, Toiletry, and Fragrance Association (CTFA) validation program (Gettings et al., 1991, 1992, 1994a, 1994b); the German eye irritation validation study (Spielmann et al., 1991, 1993, 1996); the European Commission/British Home Office (EC/HO) eye irritation validation study (Balls et al., 1995); and the European Cosmetic Toiletry and Perfumery Association (COLIPA) eye irritation study (Brantom et al., 1997). The 3T3 NRU Phototoxicity Test is a modification of the BALB/c 3T3 NRU test and involves a shorter chemical exposure and the additional application of light. The 3T3 NRU Phototoxicity Test has been fully validated (Spielmann et al., 1998a,b) and has gained regulatory acceptance.