Comparative Patch Testing with PPD-Base and PPD-Dihydrochloride: Human and Animal Data Compiled by the European Environmental Contact Dermatitis Research Group
The replacement of PPD-base 1% petrolatum (pet.) by PPD-dihydrochloride 0.5% pet. in the ICDRG standard series in 1984 seems to have reduced considerably the number of positive reactions to PPD. Therefore, the EECDRG decided to perform comparative patch tests with PPD-base and PPD-dihydrochloride. The results in human testing showed that most of the PPD sensitivities were missed by the PPD-dihydrochloride. Guinea pig experiments confirmed that PPD-dihydrochloride was less able to elicit hypersensitivity reactions than PPD-base. Similar results were obtained with groups of guinea pigs sensitized by intradermal injection to either allergen preparation. The difference in molecular weights, different liabilities in oxidative degradation to the sensitizing intermediate, or different skin penetration capabilities may account for this phenomenon.
Key wordsContact dermatitis PPD-base PPD-dihydrochloride Paraphenylenediamine False-negative reactions
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