Skin sensitization testing: the relevance of rechallenge and pretreatment with sodium lauryl sulfate in the guinea pig maximization test

The guinea pig maximization test is one of the preferred test methods for the identification of skin sensitizers. The OECD/EC test guidelines allow for the conduct of a rechallenge in case doubtful reactions are obtained after challenge. The relevance of rechallenging was investigated by performing multiple challenges (up to four) in the maximization test with four well-known sensitizers of varying strength: nickel sulfate, sulfathiazole, benzocaine, and 1-chloro-2,4-dinitrobenzene. In addition, the effect of sodium lauryl sulfate (SLS)-pretreatment during topical induction with weak sensitizers on rechallenging was investigated. In contrast to what has frequently been hypothesized, rechallenge did not result in an increase of skin reaction as compared with the reactions observed after the first treatment. SLS pretreatment was very effective in increasing the initial challenge response to weak sensitizers. Subsequent rechallenging in these cases however again showed a decrease in sensitivity of the animals.