Abstract: Aim To study the influence of electric field direction on the in vitro enhanced transdermal delivery of caffeine by electroporation. Methods Using side-by-side compartment diffusion cells method and Ag-Ag/AgCl electrodes, the transport of caffeine through human cadaver skin by electroporation (exponentially decaying pulse, pulse voltage = 350 V, pulse frequency = 4 pulses·min^-1, capacity = 22 μF, pulse length = 7 ms, 25 pulses) with different electric field directions was carried out and compared with passive diffusion and iontophoresis (0.25 mA·cm^-2, lasted for 4 h). Results (i) The cumulative quantity and flux of caffeine through human skin were increased significantly by electroporation or iontophoresis. (ii) The transport of caffeine by positive iontophoresis (with electric field from donor to receptor compartment) was significantly greater than that by negative iontophoresis (with electric field from receptor to donor compartment). (iii) The transport of caffeine by positive electroporation (with electric field from donor to receptor compartment) was similar to that by negative electroporation (with electric field from receptor to donor compartment). (iv) The enhancing effect of positive iontophoresis on the transdermal delivery of caffeine was significantly greater than that of electroporation (positive or negative). Conclusion Electric field direction significantly influences the enhancing effect of iontophoresis on the transdermal delivery of caffeine, but does not influence the enhancing effect of electroporation.

Key words: electroporation, electroporation, electric field direction, electric field direction, transdermal delivery, transdermal delivery, caffeine, caffeine