In vitro transdermal iontophoretic transport of timolol maleate: effect ofage and species

Transdermal iontophoresis would be a promising method for the systemic deli very of water soluble and ionic drugs of relatively high molecular size, in cluding peptides. In the present study, the effect of biological parameters such as age of the animal and species variation (rat, rabbit, mouse, guine a pig and human) on the transdermal iontophoretic transport was studied usi ng timolol maleate (TM) as a model drug. The iontophoretic transport of TM across the skins obtained from the rats of different age groups was found t o be similar. The results of the present study suggest that the age of the animal (Wistar rats: 1-8 months) did not appear to influence the transderma l iontophoretic transport of TM significantly. The amount of TM transported during iontophoresis (2 h) was significantly different among the different skin species. But the total amount of TM transported up to 24 h (2 h ionto phoresis + 22 h post-iontophoretic passive diffusion) was not significantly different among the different species studied. The present study provides further evidence that iontophoresis technique reduces the interspecies diff erences in the transdermal permeation of drugs, which is normally observed in passive diffusion of drugs. However, it must be noted that excised skins have been used in the present study to investigate the role of age and spe cies variation on the iontophoretic transport of TM. The influence of these parameters under in vivo conditions might be different considering the phy siological differences in different species and in the animals of different age groups. (C) 2001 Published by Elsevier Science B.V.