A comparison of low volume, Draize and in vitro eye irritation test data. III. Surfactant-based formulations

The third 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 in vitro assay protocols is presented. These investigations utilize Draize eye test and in vitro endpoint data generated previously as part of the CTFA Evaluation of Alternatives Program. LVET data were generated de novo using the same 25 representative surfactant-based personal-care formulations. In general, these formulations were minimally to moderately irritating. The linear correlation between maximum average score as determined by the Draize test (MAS) and the LVET (LVET-MAS) was 0.87; LVET-MAS values were typically about 30% lower then corresponding MAS values. 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. Regression modelling was the primary means of enabling such a comparison, the objective being to predict LVET-MAS for a given test material (and to place upper and lower prediction bounds on the range in which the LVET-MAS is anticipated to fall with high probability) based on observation of an in vitro score for that material. The degree of 95% confidence in prediction is quantified in terms of the relative widths of prediction intervals constructed about the fitted regression curves. Twenty in vitro endpoints were shown to have the greatest agreement with the LVET (these endpoints included those with low discordance rates relative to the Draize test) and were therefore selected for regression modelling. Although prediction interval widths tended to be narrower when predicting LVET-MAS compared with predicting MAS, the confidence with which the selected in vitro endpoints predicted both LVET-MAS and MAS for surfactant-based formulations was greatest when values were close to the lower or upper limits of the observed irritation range (i.e. 95% prediction interval widths were most narrow in these areas). Overall precision of LVET-MAS prediction for surfactant-based formulations was similar to that previously reported for hydroalcoholic formulations and considerably better than was reported for oil/water emulsions.