QUANTIFICATION AND LOCALIZATION OF FENTANYL AND TRH DELIVERED BY IONTOPHORESIS IN THE SKIN

Autoradiography and the technique of stripping/slicing were used in order to investigate the pathways and to quantify drug penetration into skin after iontophoresis of two model compounds: fentanyl, a lipophilic molecule and TRH, a hydrophilic molecule. Iontophoresis was performed for 1, 4 and 6 h at a mean current density of 0.33 mA/cm(2) and was compared to passive diffusion. The quantification studies showed that iontophoresis increases the drug concentration in the part of the skin limiting molecule permeation: viable skin for fentanyl and stratum corneum for TRH. Even though, besides accumulation, autoradiography allows one to localize the route of passage, observations tend to confirm that transepidermal penetration can take place and that an important route of penetration is the transappendageal pathway.