Optimizing the patch-test concentration of para-tertiary-butylcatechol: results of a prospective study with a...

Para-tertiary-butylcatechol (PTBC), which has long been patch tested internationally at 1% and 0.5% concentrations, was recently shown to induce patch-test sensitization at the 1% patch-test concentration. In order to determine a safe patch-test concentration, we performed a prospective study with lowered patch-test concentrations. A dilution series of PTBC 0.25%, 0.1%, 0.01% and 0.001% (petrolatum, pet.) was tested on the upper back. Additionally, 0.25% PTBC was tested on the left upper arm to allow patients to carry out self-examination daily. Patch tests were read on D1-3, D7, D14 and D21 after patch-test application. Patients who were not able to return for all scheduled readings were telephoned and asked to report any reaction at the patch-test sites. 65 out of the 101 patients included completed the study. A positive patch-test reaction was observed in 4 patients during D1-D3, indicating previous sensitization. 1 patient had a doubtful reaction at D3 reading. Negative patch-test results were noted in 60 patients. None of the patients developed a positive patch-test reaction during the late readings (D7-D21). Thus, patch-test sensitization was not observed in any case. Para-tertiary-butylcatechol 0.25% pet. is recommended for patch testing internationally.