Film coating of nifedipine tablets is commonly performed to reduce photo-degradation. The coating thickness of these tablets is a primary dictating factor of photo-stability. Terahertz spectroscopy enables accurate measurement of coating thickness. This study identifies a method to determine an end-point of a photo-protective coating process by using coating thickness measurements from terahertz time of flight spectroscopy (THz-TOF). For this method, nifedipine tablets, at different coating thicknesses, were placed in a photostability chamber. The illumination conditions of the coated tablets were adjusted based on the time duration of these tablets inside the chamber. A multiple linear regression model was developed with the coating thickness estimates from THz-TOF and illumination conditions information to predict the amount of drug remaining after photo-degradation (percent label claim). The prediction error of this model was 1.03% label claim in the range of 88.4–100.6% label claim. According to this model, acceptable levels of photo-protection in illumination conditions of up to approximately 700,000 lx hours was achieved at the end of the coating process (approximately 50 µm coating thickness) performed in this study. These results suggest THz-TOF as a viable process analytical technology tool for process understanding and end-point determination of a photo-protective coating process.

硝苯地平片剂的薄膜包衣通常用于减少光降解。这些片剂的包衣厚度是光稳定性的主要决定因素。太赫兹光谱法能够精确测量涂层厚度。这项研究确定了一种方法，该方法可以通过使用太赫兹飞行时间光谱（THz-TOF）中的涂层厚度测量来确定光保护涂层工艺的终点。对于这种方法，将不同包衣厚度的硝苯地平片剂放在光稳定性室内。基于这些片剂在室内的持续时间来调节包衣片剂的照明条件。利用THz-TOF的涂层厚度估算值和光照条件信息开发了一个多元线性回归模型，以预测光降解后残留的药物量（标签要求百分比）。该模型的预测误差为标签声明的1.03％，范围为88.4-100.6％。根据该模型，在这项研究中进行的涂覆过程结束时（约50 µm涂层厚度），在光照条件下达到约700,000 lx小时的可接受的光保护水平达到了可接受的水平。这些结果表明，THz-TOF是一种可行的过程分析技术工具，可用于了解过程以及确定光防护涂层工艺的终点。标签要求为4–100.6％。根据该模型，在这项研究中进行的涂覆过程结束时（约50 µm的涂层厚度），在光照条件下达到约700,000 lx小时的可接受的光防护水平达到了可接受的水平。这些结果表明，THz-TOF是一种可行的过程分析技术工具，可用于了解过程以及确定光防护涂层工艺的终点。标签要求为4–100.6％。根据该模型，在这项研究中进行的涂覆过程结束时（约50 µm涂层厚度），在光照条件下达到约700,000 lx小时的可接受的光保护水平达到了可接受的水平。这些结果表明，THz-TOF是一种可行的过程分析技术工具，可用于了解过程以及确定光防护涂层工艺的终点。