A useful technique using imaging mass spectrometry for detecting the skin distribution of topically applied lidocaine

The skin disposition of topically applied lidocaine hydrochloride was determined in steady-state skin permeation conditions by mass spectrometry imaging (MSI). The distribution of lidocaine in pig ear skin was assessed using matrix-assisted laser desorption/ionization–time-of-flight mass spectrometry (MALDI-TOF-MS) with mass images examined using BioMap software. Following the detection of intrinsic signals of lidocaine, the skin concentration–distance curve was obtained using brightness analysis ([M+H+]: m/z 235.18). Although the skin concentration profile obtained by MALDI-TOF-MS did not completely correspond with the calculated distribution obtained from the skin permeation profile, the skin concentration profile could be detected. These results demonstrated that MSI might be a useful method to determine the skin disposition of topically applied non-radiolabeled or non-fluorescent drugs