Transport Numbers in Transdermal Iontophoresis

Abstract

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.

Characterization of Ocular Iontophoretic Drug Transport of Ionic and Non-ionic Compounds in Isolated Rabbit Cornea and Conjunctiva

“…Indeed, the transport numbers of LC and BA, ratio of movement of ionic species against the total electric current, under the conditions used in the present study calculated by the theoretical equation by Mudry et al 36) were very low compared with those of coexisting ions such as Na + and Cl − (data not shown). Such coexistence of a number of ion species in the drug solution may be disadvantageous for the IP enhancement of small molecular weight ionic drugs.…”

Chemical method to enhance transungual transport and iontophoresis efficiency

“…During iontophoretic delivery, an ionic permeant competes with both extraneous and endogenous co-ions and counter-ions, which greatly decrease the transport efficiency of the ion of interest (Phipps and Gyory, 1992). Different approaches have been explored to maximize transport efficiency in transdermal iontophoresis, including simplifying the charged additives in the system (Mudry et al, 2006), increasing the mole fraction of the charged drug (Marro et al, 2001), and utilizing polymeric electrolytes (Kochhar and Imanidis, 2004). The use of a chemical enhancer to improve transungual iontophoretic transport has not been studied.…”

Princípios básicos e aplicação da iontoforese na penetração cutânea de fármacos

“…A razão máxima do transporte de um dado íon ocorre quando o número de transporte para o íon é igual a 1, isto é, quando o íon sozinho é capaz de conduzir 100% da corrente através da membrana. [48][49][50] Para otimizar o transporte iontoforético desses íons é necessário adequar dispositivos iontoforéticos e formulações compatíveis com eles, isto porque o transporte de íons é dependente de vários fatores relacionados ao dispositivo iontoforético e à formulação utilizada. Sendo assim, o fluxo iontoforético de um fármaco pode ser aumentado através da alteração de fatores elétricos, como a densidade e a natureza da corrente e o tipo de eletrodo utilizado.…”

“…56 Portanto, considerando-se que os íons presentes no interior da pele também contribuem para a condução da corrente elétrica, o número de transporte de um fármaco jamais será igual a 1. 49 Através dessas equações é possível deduzir que o transporte da corrente elétrica é competitivo entre os íons presentes no sistema. Portanto, a presença de outros íons pode reduzir o fluxo do fármaco e, conseqüentemente, sua permeação cutânea.…”