Comparison of low-volume, Draize and in vitro eye irritation test data. I. Hydroalcoholic formulations

The first phase in a series of investigations of the relationship between low-volume eye test (LVET) data, Draize eye irritation test data, and comparable data from 25 in vitro assay protocols is presented. These investigations utilize Draize eye test and in vitro assay data generated previously as part of the Cosmetic, Toiletry and Fragrance Association (CTFA) Evaluation of Alternatives Program. LVET data were generated de novo using the same 10 representative hydroalcoholic personal-care formulations. The linear correlation between maximum average score (MAS) as determined by the Draize test and the LVET (LVET-MAS) was 0.93. Comparison of in vitro assay performance with that of the LVET was determined by statistical analysis of the relationship between LVET-MAS and in vitro endpoint. As in the CTFA program, regression modelling is the primary means of enabling such a comparison. The objective is to predict LVET-MAS for a given test material (and to place upper and lower prediction interval bounds in the range in which the LVET-MAS is anticipated to fall with high probability) conditional on observing an in vitro assay score for that material. The degree of confidence in prediction is quantified in terms of the relative widths of prediction intervals constructed about the fitted regression curves. Four assays [EYTEX MPA (membrane partition assay), HET-CAM (hen's egg test-chorioallantoic membrane HET-CAM) I, neutral red release and HET-CAM II] were shown to have the greatest agreement with the LVET. These assays were also among those with low discordance rates relative to the Draize test. Prediction of LVET-MAS values from experimentally determined in vitro scores was more accurate for hydroalcoholic formulations with lower rather than higher irritancy potential.