The effect of iontophoresis on percutaneous absorption of formoterol fumarate (FF) was investigated in vitro with abdominal skin excised from guinea pig. By passive diffusion, the flux at steady state for stripped skin was about 230 times greater than that for intact skin. Therefore, it is suggested that stratum corneum is a barrier for the percutaneous absorption of FF. Penetrated amount of FF increased significantly with an increase in donor concentration from 0.035% to 0.07%. Under the constant current iontophoresis the large flux accompanied with the high applied voltage was shown at the beginning of iontophoresis. Thereafter the flux decreased with a decrease in applied voltage. Under the constant voltage iontophoresis a linear relationship between penetrated amount of FF and time was observed.
