Experimental verification of the mechanistic model for transdermal transport including iontophoresis

An experimental verification of the previously introduced model for transdermal transport (Kontturi and Murtomäki, J. Control. Release, 41 (1996) 177) is presented. The model comprises two penetration routes: an aqueous and a lipoidal pathway. Lipophilicity of the drug determines which route the drug uses. Constant potential iontophoresis can be used to evaluate the relative proportions of the two competing pathways. beta-blockers sotalol, timolol and propranolol, whose water-octanol partition coefficients span three orders of magnitude, are used as model compounds. Experiments reinforce the predictions of the model in that iontophoresis enhances the flux of the most hydrophilic drug, sotalol, the most whereas the flux of the least hydrophilic drug, propranolol, is enhanced the least. The effect of electroosmosis has now been included in the model.