Methyldibromoglutaronitrile allergy: relationship between patch test and repeated open application test thresholds.

Methyldibromoglutaronitrile (MDBGN) is a preservative, which was approved for use in cosmetics in the mid-1980s. The incidence of allergy to MDBGN rose during the 1990s, but is now decreasing due to regulatory intervention. Experimental studies with other allergens have shown a significant relationship between the patch test and the repeated open application test (ROAT) reactivity. To study the relationship between elicitation threshold doses at single occluded exposure and repeated open application, using MDBGN as the allergen. Eighteen subjects allergic to MDBGN were tested with a dilution series of MDBGN in a patch test and a ROAT (duration up to 21 days). Seventeen people with no MDBGN allergy were included as a control group for the ROAT. The response frequency for the ROAT (in microg MDBGN cm(-2) per application) was significantly higher than the response frequency for the patch test, while the response frequency for the accumulated ROAT dose, at 1, 2 and 3 weeks was very similar to the patch test response frequency; indeed there was no statistical significant difference. For elicitation of MDBGN allergy the response frequency for the patch test is lower than the response frequency (per application) for the ROAT, but approximately the same as the response frequency for the accumulated ROAT doses. This is important for risk assessment in general.