Drug distribution in human hair by infrared microscopy

Localization of drug metabolites within human hair is important in determining the pharmacokinetics of drug incorporation in hair. This information is critical to validate drug testing data from hair. Microspectroscopic probing of small areas within longitudinally microtomed hair sections provides a profile of the deposition of drug along a growth line and thus indicates localization as a function of time. Probing across individual hairs may reveal the hydrophobic/hydrophilic characteristics of the substance. Hydrophobic drugs tend to bind to the central core or medulla of the hair while hydrophilic drugs tend to be spread throughout the cortex of the hair and appear, generally, in lower concentrations per dose. Profiles of distribution with high spatial resolutions of the regions of the hair are necessary for these determinations. This information is available to a certain extent in normal infrared microscopy and enhanced in synchrotron powered infrared microscopy.