Near-infrared spectroscopy-based methods for quantitative determination of active pharmaceutical ingredient in transdermal gel formulations

Semi-solid pharmaceutical forms, like topical and transdermal products, are widely used for medical purposes since they provide convenient and pain-free treatment for patients. In this study, two transdermal gel formulations with different active pharmaceutical ingredients were analyzed with near-infrared spectrophotometers with three distinct optical arrangements (dispersive, Fourier transform, and diode-array spectrophotometers) for the measurement of active pharmaceutical ingredient concentration. The reference concentrations were measured with high-performance liquid chromatography methods.The developing of calibration for reference concentrations based on near-infrared spectra was performed using partial least squares regression. The spectra from near-infrared spectrophotometer with diode-array optical arrangement presented the best root mean square error of cross-validation results with 0.045% and 0.144% for the two active pharmaceutical ingredients. The root mean square error of cross-validation using dispersive spectra were 0.125% and 0.193% and using Fourier transform spectra were 0.130% and 0.344% for the active pharmaceutical ingredients. The results of partial least squares regression were confirmed using simulated spectra based on the measured datasets.Near-infrared spectroscopy can be used successfully for the quantitative measurement of active pharmaceutical ingredient concentration in transdermal gel formulations. The type of optical arrangements of spectrophotometers can influence the performance of calibrations and have to be optimized case by case.