Nickel-sulphate-induced contact dermatitis in the guinea pig maximization test: a dose-response study.

Nickel sulphate is a sensitizer in guinea pigs, but the frequency of sensitization varies from study to study. The dose-response relationship for NiSO4.6H2O was evaluated in the guinea pig maximization test in this study. 6 intradermal (0.01%-3.0% aq.) and 6 topical (0.25%-10.0% pet.) concentrations were chosen for induction and NiSO4.6H2O 1% pet. was used for challenge, based on the absence of skin irritation in a pilot study. Blind reading was performed. A logistic dose-response model was applied to the challenge results. At 48 h, a linear relationship was obtained between the intradermal induction dose (but not topical dose) and the response, resulting in a maximum sensitization rate of 40% after 3% i.d. The reactivity disappeared at re-challenge 1 week later. Following a booster closed patch on day 35, using NiSO4 10% pet., the animals were challenged with NiSO4 2% pet. and statistical analyses of 72-h readings revealed a non-linear dose-response relationship, giving a maximum response frequency of 40% after initial induction with NiSO4 3% i.d. and 2% topical.