Skin absorption and metabolism of [14C]-labeled C12-benzalkonium chloride (C12-BKC) in ex vivo porcine ear skin using UPLC-β-RAM analysis.

Benzalkonium chloride is a quaternary ammonium disinfectant widely used in pharmaceutical, cosmetic, and household products, raising concerns regarding dermal exposure and systemic safety. This study evaluated the percutaneous absorption and cutaneous metabolic fate of [14C]-labeled C12-benzalkonium chloride using an ex vivo porcine ear skin model. To assess the effect of skin viability, both viable and freeze-killed skin discs were examined following topical application of the radiolabeled compound. Radioactivity from skin surface washes, tissue extracts, and receptor media was analyzed by ultra-performance liquid chromatography coupled with a flow-through beta-radioactivity detector. The overall mass balance ranged from 79.0 to 93.6%. While the overall distribution patterns were similar between skin types, freeze-killed skin exhibited significantly higher tissue retention, particularly in the secondary isopropyl alcohol extract, suggesting a structural damage-induced reservoir effect. In contrast, viable skin demonstrated more rapid permeation into the receptor medium, reflecting preserved skin barrier function. Metabolic profiling showed that the intact parent compound accounted for more than 85% of total radioactivity across all compartments. Minor secondary radiochemical peaks were considered likely to represent non-enzymatic degradation products, as their presence was independent of skin viability. Collectively, these findings indicate that C12-benzalkonium chloride permeates porcine skin predominantly in its parent form and undergoes negligible cutaneous biotransformation. The results suggest that systemic exposure to benzalkonium chloride is primarily governed by permeation kinetics and skin barrier integrity rather than metabolic transformation.