Epidermis, iontophoretic

C. Iontophoretic Transport Pathways Across the Stratum Corneum and Epidermis... 

Excised epidermis Solutes used in excised epidermal studies are also predominantly low-MW polar solutes, as shown in Table 3. However, in a number of studies, the iontophoretic transport of uncharged solutes has also been demonstrated. The phenomenon of electro-osmotic flow will be discussed further in Section II.C. Excised skin used in transdermal studies includes hairless mouse, nude rat, shed snake skin, and human epidermis. The human epidermis is used in one of two forms, dermatomed [28,29] or heat separated [30]. 

Singh and Roberts [63] have shown that iontophoretic delivery through intact epidermis yields deeper tissue concentrations, identical to that after dermal delivery. Figure 4 shows similar tissue concentrations for lidocaine and salicylate after iontophoretic delivery through intact skin and passive application of these solutes to the dermis. It is therefore concluded that iontophoresis... 

Transient solutions for the Nemst-Einstein equation have been derived assuming a constant source concentration [69]. An approximate solution may be obtained when the decline in source concentration is small over the time period of the study by assuming (a) a constant iontophoretic permeability coefficient Fionp (b) the donor iontophoretic compartment is a well-stirred solution (c) sink conditions exist and (d) the solute concentration in the donor solution Q of volume changes at a rate equal to the total flux JjA out of the compartment into the outer layer of the epidermis ... 

Figure 9 (A) lontophoretic flux of various cations across excised pig skin versus molecular weight. The donor concentration was 1.0 M of drug as chloride salt. (Data from Ref. 108.) Key. ( ) monovalent ions, (O) divalent ions. (B) Normalized cathodal iontophoretic flux of anionic solutes across hairless mice versus molecular weight. (Data from Ref. 109.) (C) Cathodal iontophoretic permeability coefficient of alkanoic acid across nude rat skin versus molecular weight. (From Ref. 64.) (D) Comparison of transport number and molecular weight in human epidermis.

The determinants of in vivo iontophoretic delivery and subsequent tissue distribution have been studied to only a limited extent. The concentrations of solute in a given tissue below the epidermis will be dependent on the flux of solute into that tissue and on the clearance of solute from the tissue [62,110]. Clearance of a solute by the local blood supply is an important concern, given... 

Cross, S. E. and Roberts, M. S. The importance of dermal blood supply and the epidermis on the transdermal iontophoretic delivery of monovalent cations. J. Pharm. Sci. 84 584, 1995. 

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