Objectives The feasibility of transdermal delivery of tramadol, a centrally acting analgesic, by anodal iontophoresis using Ag/AgCl electrodes was investigated in vitro and in vivo.
Methods To examine the effect of species variation and current strength on skin permeability of tramadol, in-vitro skin permeation studies were performed using porcine ear skin, guinea-pig abdominal skin and hairless mouse abdominal skin as the membrane. In an in-vivo pharmacokinetic study, an iontophoretic patch system was applied to the abdominal skin of conscious guinea pigs with a constant current supply (250 mu A/cm(2)) for 6 h. An intravenous injection group to determine the pharmacokinetic parameters for estimation of the transdermal absorption rate in guinea pigs was also included.
Key findings The in-vitro steady-state skin permeation flux of tramadol current-dependently increased without significant differences among the three different skin types. In the in-vivo pharmacokinetic study, plasma concentrations of tramadol steadily increased and reached steady state (336 ng/ml) 3 h after initiation of current supply, and the in-vivo steady-state transdermal absorption rate was 499 mu g/cm(2) per h as calculated by a constrained numeric deconvolution method.
Conclusions The present study reveals that anodal iontophoresis provides current-controlled transdermal delivery of tramadol without significant interspecies differences, and enables the delivery of therapeutic amounts of tramadol.