The preservative iodopropynyl butylcarbamate: frequency of allergic reactions and diagnostic considerations.

The preservative iodopropynyl butylcarbamate (IPBC) (0.1% in petrolatum) was tested in 4883 consecutive patients for 18 months between January 1998 and June 1999. With regard to the MOAHLFA-Index, the study population comprised 37% males; 17% with occupational and 19% with atopic dermatitis; 31% with hand, 10% with leg and 17% with face dermatitis; 61% were age 40 and above. According to readings at D3, 0.3% were allergic to IPBC, with 14 + and 2 + + reactions. Doubtful or irritant reactions occurred twice as frequently. Patients exposed for 24 h (n = 1814) reacted less frequently (0.1%) than the remaining patients exposed for 48 h (0.5%). Considering the possibility that a certain proportion of + reactions could be false positive, the reaction pattern was evaluated. More than 80% of the positive reactions displayed a crescendo or plateau time pattern. Furthermore, 18 of 43 doubtful reactions (?) appeared as late as D3 (thus, these could be false negative), whereas the majority of doubtful reactions occurred earlier and displayed a decrescendo pattern (corresponding to a typical irritant pattern). In conclusion, the large proportion of '?' reactions may be due not only to the irritant potential of the substance, but also to test concentrations not being high enough to elicit an allergic reaction. We propose that higher concentrations of IPBC (0.3%) should be evaluated in a study also addressing suitable validation tests like ROAT or PUT.