In vitro dermal absorption of Lauryl Isoquinolinium Bromide (LIB) from a cosmetic cream formulation

Lauryl Isoquinolinium Bromide (LIB; CAS No. 93-23-2) is used as a preservative agent and also for its antistatic, deodorant, and surfactant properties in cosmetics at a maximum concentration of 0.05% in Korea and Japan. Since skin absorption of LIB has not been reported, we conducted in vitro dermal absorption study of LIB according to US FDA and Korea Ministry of Food and Drug Safety guidelines. Before the dermal absorption study, analytical methods were developed using liquid chromatography-mass spectrometry (LC-MS/MS) for quantitation of LIB in various matrices of swab, stratum corneum (SC), skin (dermis + epidermis), and receptor fluid. This LIB analytical method showed good linearity (r²=0.9984-0.9995), accuracy (91.8-113.7%) and precision (0.6-8.5%). Franz diffusion cell was used to determine dermal absorption of LIB using commercially available mini pig skin. For cream formulation, 0.038% of LIB was applied to the skin at 10 μl/cm². After 24 h of application, the skin surface was wiped with an alcohol swab, SC was collected by tape stripping, and the remaining skin was collected for analysis. As a result, the total dermal absorption rate of LIB was determined to be 0.08 ± 0.04 μg/cm² (2.18 ± 1.06%) from the 0.038% cream formulation.