This Article Full Text Full Text (PDF) All Versions of this Article: biophysj.105.074609v1 90/8/2822    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Mudry, B. Articles by Delgado-Charro, M. B. Search for Related Content PubMed PubMed Citation Articles by Mudry, B. Articles by Delgado-Charro, M. B.

Transport Numbers in Transdermal Iontophoresis

Blaise Mudry ^*, Richard H. Guy ^*  and M. Begoña Delgado-Charro 

^* School of Pharmaceutical Sciences, University of Geneva, Geneva, Switzerland; and Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom

Correspondence: Address reprint requests to M. Begoña Delgado-Charro, Dept. of Pharmacy and Pharmacology, University of Bath, Claverton Down, Bath, BA2 7AY, UK. E-mail: B.Delgado-Charro{at}bath.ac.uk.

Parameters determining ionic transport numbers in transdermal iontophoresis have been characterized. The transport number of an ion (its ability to carry charge) is key to its iontophoretic delivery or extraction across the skin. Using small inorganic ions, the roles of molar fraction and mobility of the co- and counterions present have been demonstrated. A direct, constant current was applied across mammalian skin in vitro. Cations were anodally delivered from either simple M⁺Cl^– solutions (single-ion case, M⁺ = sodium, lithium, ammonium, potassium), or binary and quaternary mixtures thereof. Transport numbers were deduced from ion fluxes. In the single-ion case, maximum cationic fluxes directly related to the corresponding ionic aqueous mobilities were found. Addition of co-ions decreased the transport numbers of all cations relative to the single-ion case, the degree of effect depending upon the molar fraction and mobility of the species involved. With chloride as the principal counterion competing to carry current across the skin (the in vivo situation), a maximum limit on the single or collective cation transport number was 0.6–0.8. Overall, these results demonstrate how current flowing across the skin during transdermal iontophoresis is distributed between competing ions, and establish simple rules with which to optimize transdermal iontophoretic transport.