Iontophoretic flux model

Passive and Iontophoretic Fluxes of Three Model Cationic Drugs across Different Skin Barriers... 

A third model of iontophoretic flux arises from the idea of a retardation in the entry of solute ions into, and movement via, pores in the skin. Renkin [101] described a pore-restriction model for the diffusion of uncharged molecules through water-filled cylindrical pores. He suggested that diffusion would be restricted relative to the movement in aqueous solution by (a) steric hindrance inhibiting the entry of solute ions into the pore, and (b) hindrance due to frictional forces during the movement of solute ions through the pore. According to this model, Pjo , may be expressed by... 

As discussed, a number of studies have examined the effect of vasoactive drugs on percutaneons absorption. We therefore limit this discnssion to the more detailed investigations. Mnch of this early work was undertaken nsing both the IPPSF (Riviere and Williams, 1991) and anesthetized weanling pig model (Riviere etal., 1992). They reported that the vasodilator tolazoline significantly increased lidocaine flux compared to that observed in vitro, whereas norepinephrine (a vasoconstrictor) sigruficantly decreased lidocaine flux in the IPPSF (Riviere and Williams, 1991). Tolazoline shortened and norepinephrine increased the mean absorption time. Neither of these effects conld be replicated in the in vitro model. Their subsequent work in the anesthetized pig model showed that, in tissue samples taken 4 h after a 1-h iontophoretic treatment period, tolazoline had decreased underlying tissue concentrations of lidocaine, and norepinephrine had increased tissue levels compared to those observed when lidocaine was administered alone (Riviere etal., 1992). Subsequently, Williams and Riviere (1993) used a three-compartment pharmacokinetic model to describe these results. 

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