Metabolic conversion of cyoctol during skin passage in humans

Upon application of 14C-labeled cyoctol to the forearm of healthy volunteers, no parent cyoctol was detectable in ipsilateral blood plasma. The 14C activity was largely accounted for by a component with higher lipophilicity than the parent compound, as justified from their HPLC retention. Thus, this study suggests that human skin is capable of nearly complete cutaneous first-pass metabolism, resulting in negligible systemic availability of cyoctol. In a comparable experiment, rabbits were also able to convert cyoctol during skin absorption to a more lipophilic metabolite, which was identified as the palmitoleic acid ester of O-demethylated cyoctol by GC/MS. However, chromatographic evidence indicates that the human ipsilateral metabolite differs from the rabbit cyoctol metabolite.