Photostability of Crystalline Versus Amorphous Nifedipine and Nimodipine
True solid-state photostability of the drugs nifedipine and nimodipine was investigated during exposure to UV-visible radiation. Photostability was studied on a small scale as thin films of approximately 1mg drug, which contained either amorphous or re-crystallised stable phases. High-performance li...
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Published in | Journal of pharmaceutical sciences Vol. 102; no. 6; pp. 1883 - 1894 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Hoboken
Elsevier Inc
01.06.2013
Wiley Subscription Services, Inc., A Wiley Company Elsevier Limited |
Subjects | |
Online Access | Get full text |
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Summary: | True solid-state photostability of the drugs nifedipine and nimodipine was investigated during exposure to UV-visible radiation. Photostability was studied on a small scale as thin films of approximately 1mg drug, which contained either amorphous or re-crystallised stable phases. High-performance liquid chromatography analysis revealed a greater rate and extent of decomposition for the amorphous phases. Photoexposed amorphous nifedipine exhibited approximately 1.8-fold larger first-order decomposition rate constant (k) relative to its crystalline phase. The increase in k was more significant for photoexposed amorphous nimodipine at approximately sixfold relative to its crystalline phase. Photodecomposition in scaled-up samples of the stable crystalline phases for both drugs was monitored with X-ray diffraction in Bragg-Brentano geometry. The similarities in the calculated photodecomposition extents to results from small scale validated the specificity of the X-ray analysis technique to the photodecomposition region. The considerably faster decomposition rates in small-scale studies were attributed to a maximised surface area (A) for quantity (m0) of exposed drug. Kinetic interpretations of true solid-state stability should consider the sample solid dimensions in terms of the direct exposed A and m0 in the photodecomposition region, that is, outer layers in solid. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0022-3549 1520-6017 |
DOI: | 10.1002/jps.23533 |