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

Autoradiography and the technique of stripping/slicing were used in or der to investigate the pathways and to quantify drug penetration into skin after iontophoresis of two model compounds: fentanyl, a lipophili c molecule and TRH, a hydrophilic molecule. Iontophoresis was performe d 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 co rneum for TRH. Even though, besides accumulation, autoradiography allo ws one to localize the route of passage, observations tend to confirm that transepidermal penetration can take place and that an important r oute of penetration is the transappendageal pathway.