Evaluation of Photostability of Drugs and Design for Photostabilization of the Drugs

（1）采用高效液相色谱法和傅立叶变换红外反射-吸收光谱法（FT-IR-RAS），在非破坏性条件下考察了硝苯地平粉末和片剂的粒度对光稳定性的影响，并根据<-1>荧光灯照射前后FT-IR-RAS光谱中1682 cm ~ 2处的C=O伸缩振动吸收，测定了硝苯地平片剂表面的含量。硝苯地平粉末的表观光降解常数随粒径的减小而增大，而硝苯地平片剂的表观光降解常数与粒径无关。（2）研究了维A酸生育酚在三种光源下的光稳定性，冷白色荧光灯、UV-A荧光灯和D 65荧光灯。冷白色荧光灯和UV-A荧光灯的组合以及具有类似于直射日光的相对光谱功率分布的D 65灯分别对应于ICH指南中的选项2和1。在这些光源下，光降解明显遵循二级动力学，并且D 65灯照射下的降解速率常数大于冷白色荧光灯照射下的降解速率常数。在480 nm以下的可见光下，该药物易被降解，在420 nm附近降解最明显，并呈波长依赖性，氧化降解速率随温度升高略有加快。在低于20 kPa的氧分压下，降解速率常数随氧分压的增大而迅速增大。

(1)Effect of the particle size on the photostability of nifedipine powder and its tablet was investingated using HPLC method and Fourier-transformed infrared reflection-absorption spectroscopy (FT-IR-RAS) under the non-destructive condition.The nifedipine content on the surface of the tablet was determined based on the absorption at 1682 cm^<-1> attributable to the C=O stretch vibration in FT-IR-RAS spectra before and after irradiation by fluorescent lamp. The apparent photodegradation constant of nifedipine powder increased with decrease of the particle size, while that of its tablet was approximately constant irrespective of particle size.(2)The photostability of tretinoin tocoferil was investigated under irradiation with three kinds of lamps, i.e., a cool white fluorescent lamp, a UV-A fluorescent lamp and a D65 fluorescent lamp. A combination of the cool white fluorescent lamp and the UV-A fluorescent lamp, and the D65 lamp having relative spectral power distribution similar to that of direct daylight, correspond to options 2 and 1 in ICH Guidelines, respectively. The photodegradation apparently followed second-order kinetics under these light sources and the degradation rate constant under exposure by the D65 lamp was larger than that by the cool white fluorescent lamp. The drug was susceptible to degradation by visible light below 480 nm and was degraded most remarkably at around 420 nm, showing a wavelength- dependency.The rate of oxidative degradation was slightly accelerated with the rise of temperature. The degradation rate constant rapidly increased in proportion to partial pressure of oxygen below 20kPa.