Spectroscopic and HPLC Studies of Photodegradation of Nilvadipine.

Photochemical decomposition of nilvadipine (NV), a derivative of 1,4-dihydropyridine (DHP), was studied. Photodegradation was carried out in the conditions recommended in the first version of the document issued by the International Conference on Harmonization (ICH), currently in force in the studies of photochemical stability of drugs and therapeutic substances. Methanol solutions of NV were irradiated with a high-pressure mercury arc lamp, type HBO 200 (300 400 nm). The maximum absorption of radiation at 365 nm was achieved by applying the interference filter and Wood's filter. The assessment of NV photodegradation was made on the basis of the UV spectrophotometric and highperformance liquid chromatographic (HPLC) methods. Quantitatively, the process was described with the calculated rate constants of decomposition k, time of decomposition of 50% of the compound t[SUB0.5], and time of decomposition of 10% of the compound t[SUB0.1]. The two methods applied allowed a determination of the kinetic parameters of NV photodegradation from the relationship In c = f(t). Using the Reinecke salt as a chemical actinometer, apparent quantum yields of photodegradation were obtained; after extrapolation to the time of irradiation zero, these gave the actual quantum yield (&PHgr; = 7.3. 10[SUP-5]). The quantum yield of fluorescence at lamda[SUBexe = 375 nm was about 9.3.10[SUP-4]. The methods used for evaluation of NV photodegradation were subjected to validation, and results of the analytical methods were statistically assessed by Snedecor F and Student t tests. The former test revealed no statistically significant difference between the variances obtained by the HPLC and UV spectrophotometric methods. Also, verification of the zero hypothesis of the Student t test on equality of means of the results obtained gave no significant differences between the two methods. [ABSTRACT FROM AUTHOR]

Copyright of Drug Development & Industrial Pharmacy is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)