Phototoxicity of olaquindox in the rat

Because of its photoallergic properties quindoxin, a growth promoting feed additive used for example in cattle raising, has been taken off the market. Recently, it appeared that the quindoxin derived olaquindox (olaq), used for the same purpose, also produces these light-induced side effects. In this study, phototoxicity of olaq was investigated by comparing four groups of rats with a different daily regime: 1 = light plus olaq, 2 = dark plus olaq, 3 = light (no olaq), 4 = dark (no olaq). It appeared that rats of group 2 excreted per day approximately 60 per cent of their daily dose as olaq and approximately 2 per cent as OLAQ-4-monoxide, whereas these figures were approximately 19 per cent and 30 per cent, respectively, for the light-exposed animals. Besides, rats of group 1 only, suffered from severe erythema, oedema and necrosis of the ears after four days treatment. It is probable that olaq, photoactivated in the skin, forms a reactive oxaziridine, analogous to what has been found with the tranquilliser chlordiazepoxide (Librium; Hoffmann La Roche), another imino-N-oxide.