Evaluation of percutaneous penetration of insect repellents and sunscreens

Insect repellents and sunscreens are over-the-counter consumer care products that have been extensively used by the general public for decades. With an increasingly awareness of mosquito-borne diseases and detrimental effects of UV radiation from the sun, concurrent use of both repellent and sunscreen preparations has become prevalent. Repellent DEET and sunscreen oxybenzone had been investigated individually for their percutaneous properties in the past; however, no study has been carried out to assess their transdermal characterization from a concurrent application.;DEET and oxybenzone permeated across all study membranes in vitro. A synergistic permeation was observed when the two compounds were present simultaneously. This penetration enhancement was also dependent on the type of dissolving solvent and the concentration of both DEET and oxybenzone used. The penetration patterns were found to be identical among three membranes tested. In vivo studies indicated percutaneous penetration and systemic absorption of DEET and oxybenzone from commercial preparations. Combined repellent/sunscreen formulation demonstrated a significant higher percutaneous penetration of DEET and oxybenzone than its individual counterparts. DEET penetrated through the skin at a faster rate than oxybenzone. Oxybenzone and its major metabolites were detected in the urine samples 48 hours after the topical administration; however, no DEET was found in the urine samples.;Percutaneous permeation and systemic absorption of repellent DEET and sunscreen oxybenzone was systematically investigated in this thesis. Transdermal enhancement of DEET and oxybenzone from a concurrent application was first observed and reported. As topical preparations, both insect repellents and sunscreens should remain on the surface of skin with minimal systemic absorption; an increased percutaneous permeation observed in this thesis would potentiate undesirable characteristics and compromise protection efficacy of repellent and sunscreen products.;In this thesis, in vitro diffusion experimentation was utilized to systematically evaluate transmembrane behaviors of DEET and oxybenzone across three different membrane models. Permeation properties were assessed with individual DEET or oxybenzone, as well as with the combination of both compounds. The influence of dissolving solvent, application concentration and temperature on diffusion process was also studied. Further in vivo studies were performed using three commercially available repellent and sunscreen products in a piglet model. Percutaneous penetration and systemic absorption of DEET and oxybenzone after topical skin application were evaluated using tape stripping. Concentrations of DEET, oxybenzone and their primary metabolites in biological samples were analyzed using a validated HPLC assay.