Percutaneous absorption, disposition, metabolism, and excretion of 14C-labelled Cyoctol in humans after a single dermal application

14C-labelled cyoctol was applied in an ethanolic solution to the forearm of four young healthy volunteers for 8 h under non-occluding conditions, to investigate its absorption, disposition, and excretion after a single dermal application. Urine and feces were collected to determine the absorbed amounts of radioactivity, while ipsi- and contralateral blood samples were taken in order to obtain an insight into the kinetics of the penetration and elimination processes. The application area was stripped with cellophane adhesive tape at three different time points to study the retention of cyoctol in the stratum comeum. Cyoctol was found to be absorbed by human skin at levels of approx. 10% of the applied dose and appeared to penetrate at a relatively fast rate. Radioactivity accumulated neither in the skin nor in any other site in the body as total recovery values were close to 100% at 120 h after removal of the dose. Radioactivity was eliminated primarily through the kidneys ( ⪢ 99%) in the form of polar metabolites. Another interesting phenomenon was that cyoctol was completely metabolized when passing through the skin as no unchanged Cyoctol could be detected in ipsilateral plasma samples. This may eliminate the occurrence of adverse systemic effects after dermal application