UC San Diego

A collection of data on the Draize rabbit eye test (Cronin et al., 1994) has been analysed using a set of physicochemical descriptors that we have previously put forward. These descriptors are compound (or solute) parameters as follows: R₂ is an excess molar refraction, p₂ ^H is the polarizability/dipolarity, ∑a^H ₂ and ∑b₂ ^H are the effective hydrogen bond acidity and basicity, and logL¹⁶ is a descriptor where L¹⁶ is the vapour-hexadecane solubility at 25°C. When applied to Draize eye scores (DESs) for 38 pure bulk liquids, a very poor equation was obtained. However, when the DES values were correlated as log(DES/P^o), where P^o is the liquid vapour pressure, an excellent equation was found. On transforming the calculated log(DES/P^o) values back to calculated DES values, there was good agreement with the original DES values. It is suggested that the DES/P^o values refer to transfer of the irritant from the vapour phase to the biophase, and that the success of the present treatment demonstrates that for the pure liquids studied, a major factor in the Draize eye test is simply the transfer of the liquid (or the vapour) to the biological system.