In vitro percutaneous absorptiometry by simultaneous measurement using the photoacoustic method and absorbance

A novel in vitro percutaneous absorptiometry utilizing a portable open-ended photoacoustic (PA) cell as the longitudinal diffusion cell was developed. With this system it was feasible to measure the reduction of drug applied to a membrane by the PA method and the amount of drug penetrating the membrane to the diffusion cell by absorbance, simultaneously in real time. A shikonin ointment prepared in a hydrocarbon vehicle was used as the model sample. The in vitro percutaneous absorptiometry was performed by means of a physiological saline solution and the skin of a hairless mouse. As a result, after the lag time the absorbance increased in proportion to time, whereas the PA signal reduced in proportion to the square root of time. As the signal obtained by the PA method corresponds to the amount of drug released from the ointment, a good correlation with Higuchi's theory is attained. Consequently, these results suggested the usefulness of this novel percutaneous absorptiometry technique which utilizes the PA method.