[The pharmacokinetics of light-protective agents by photoacoustic spectroscopy]

We report on in vivo investigations by photoacoustic spectroscopy on the liberation and horny-layer penetration of UV-absorbing drugs from topically applied vehicle films. This spectroscopic technique can be used to determine the absorption of light in the skin with a depth resolution adequate for the 12-microns-thick horny layer and to gain information on temporal variations in the concentration profile of drug penetrating into the horny layer. Experimental results are presented for the UV-absorbing drugs Uvinul T 150 and P 25 applied to the skin in different vehicles. The results are discussed with reference to model calculations demonstrating the influence of different rate-determining steps on temporal variations in concentration profiles.