ABSTRACT
The science of dermatokinetics is de‘ned as the study of the penetration dynamics of a topically applied active (usually a drug) through the skin over time. To this end, it is obvious that accurate methods are needed to quantify the amount of active in the skin tissue. Since the aim is to study the same sample (skin) over time, it is necessary that the measuring methods are nondestructive. Furthermore, in order not to disturb the naturally evolving kinetics of drug penetration, these methods need not only be nondestructive but also noninvasive. Finally, although in vitro models (such as skin equivalents) or ex vivo models (excised skin from cadavers or from surgeries) are useful as a ‘rst step to understand dermatokinetics, the ultimate goal is to be able to study drug penetration in human skin in vivo. The techniques that ful‘ll all the above requirements are based on the principle of interrogating the skin tissue
7.1 Introduction to Spectroscopic Techniques Used in Dermatokinetic Studies ........................................................................ 175
7.2 Fundamentals of Tissue Spectroscopy ......................................................... 176 7.2.1 Light Scattering ................................................................................ 177 7.2.2 Light Absorption ............................................................................... 177
7.3 Applications .................................................................................................. 177 7.3.1 Diffuse Re±ectance Spectroscopy in Dermatokinetics .................... 178 7.3.2 Fluorescence Spectroscopy in Dermatokinetics ............................... 180 7.3.3 Infrared Spectroscopy in Dermatokinetics....................................... 182 7.3.4 Raman Spectroscopy in Dermatokinetics ........................................ 184 7.3.5 Other Methods: Photoacoustic Spectroscopy and Higher-Order
Optical Spectroscopies ..................................................................... 186 7.4 Summary ...................................................................................................... 187 Bibliography .......................................................................................................... 188
using an optical probe. In other words, while light* is allowed to travel through and interact with the sample, part of the light is collected and analyzed. This analysis of the collected light, known as spectroscopy, is able to provide us with information regarding the concentration (and in some cases the distribution) of the drug in the tissue at a particular point in time.
