2-LAYER MEMBRANE MODEL FOR IONTOPHORETIC DRUG TRANSPORT THROUGH EXCISED RAT SKIN

Iontophoretic and passive transport of an ionized drug (sulfisoxazole) across excised rat skin was studied using a two-chamber cell with fou r electrodes under successive experimental conditions: without electri cal current (stage-1) and with electrical current (stage-II). Two iont ophoretic/diffusion models, i.e. a one-layer membrane model and a two- layer membrane model, in which a difference in the electrical potentia l gradient was taken into account between the stratum corneum and epid ermis/dermis layer, were constructed to describe the non-steady-state drug permeation process during iontophoresis. The observed iontophoret ic lag-time was two times greater than the calculated value based on t he one-layer membrane model. According to the two-layer membrane model , the calculated iontophoretic lag-time agreed with the observed value . It was revealed by model adaptation to the observed data that the st ratum corneum fraction of the electro-chemical potential difference ac ross the whole skin caused by the iontophoresis was around 90%. This r esult was consistent with the observation that the direct current resi stance of whole skin was seven times greater than that of stripped ski n.