Multilayered dermal subcompartments for modeling chemical absorption

Dermal penetration of chemicals and drugs is of concern to both toxicologists and pharmacologists. Environmental professionals try to limit exposure to chemicals using protective clothing and gloves or barrier creams to trap chemicals. Drug developers try to enhance penetration of chemicals through the skin for medical purposes. Both can use predictive biologically-based mathematical models to assist in understanding the processes involved. These models are especially useful when they are based on physiological and biochemical parameters which can be measured in the laboratory. Appropriately validated models based on conservation of mass, diffusion and chemical transport by flow can be predictive of human exposures. In this paper we develop two new physiologically-based pharmacokinetic (PBPK) skin models to predict blood concentrations of dibromomethane in rats after skin-only vapor exposures. These new models improve the predictions of the blood concentrations especially at the beginning of the exposures. Sensitivity analysis shows that the permeability constants followed by partition coefficients have the most impact on blood concentration predictions. With proper validation the new models could be used to improve species, dose, and duration extrapolations of chemical or drug penetration. They could also be used to investigate and predict concentrations of drugs or chemicals in the skin.