Non-destructive analysis of tulobuterol crystal reservoir-type transdermal tapes using near infrared spectroscopy and imaging

A non-destructive method for analyzing crystalline tulobuterol (TBR; a bronchodilator [β2-blocker]) in transdermal drug delivery system tapes with a crystal reservoir system was developed. A near infrared spectroscopy (NIRS) and a near infrared spectroscopic imaging (NIRI) were used to investigate the distribution of TBR crystals in transdermal tapes. The characteristic peak derived from a first overtone of secondary amine which appears based on crystal growth was used for the detection of crystals. NIR images were composed by the integrated values of that peak at each pixel. The time-course analysis by NIRS showed that the intensity of the peaks gradually increased, and the intensity reached a plateau between day 30 and day 42 after preparation of the model tapes. The authors observed the growth and distribution of TBR crystals in small areas in several types of matrices by NIRI time-course measurement. The authors also found that a macroscopic map can provide a rough distribution map of crystalline TBR in a whole matrix. In the case in which a tape distributed from the innovator was examined, the characteristic peak was also detected through a liner or a supporting board, by transmittance-reflectance NIR measurement.