title: Influence of solubility and permeant size on absorption and metabolism of xenobiotics in rabbit skin.
abstract: 1 In order to obtain an understanding of the risks associated with dermal uptake of xenobiotics it is necessary to investigate the principles governing percutaneous absorption and metabolism. The single-pass perfused rabbit ear served as a convenient model for the simultaneous study of absorption and metabolism of a variety of substances. We found: 2 When substances are applied in a lipophilic vehicle the permeation coefficient Kr is notably decreased when the distribution coefficient (n-octanol/perfusion buffer (pH 7.4)) Poct. exceeds 2000, Kr also decreases with increasing molecular weight. 3 Substances which are in the ionized state at pH 7.4 may have a higher permeation coefficient than would be expected from Poct. or by molecular weight. 4 The partition of a drug from the stratum corneum to the epidermal enzymes controls the extent of its metabolism. However, substances with increased solubility at physiological pH are metabolized to a lesser extent than expected from their absorption rate. 5 The decrease in percutaneous absorption and metabolism of a substance with a Poct. exceeding 2000 is consistent with the assumption that high lipophilicity hinders partition of the substance from the stratum corneum to the viable metabolizing tissue.
authors.affiliation: Walther-Straub-Institut für Pharmakologie und Toxikologie, Medizinische Fakultät, Ludwig-Maximilians-Universität, München, Germany.
authors.forename: G E
authors.initials: GE
authors.lastname: Bast
mesh_terms: D000279:Administration, Cutaneous; D000818:Animals; D001682:Biological Availability; D004431:Ear, External; D010316:Particle Size; D010539:Permeability; D014677:Pharmaceutical Vehicles / Q000378:metabolism; D011817:Rabbits; D012867:Skin / Q000378:metabolism*; D012869:Skin Absorption; D012995:Solubility; D015262:Xenobiotics / Q000008:administration & dosage / Q000378:metabolism*
chemical_list: D014677:Pharmaceutical Vehicles; D015262:Xenobiotics