Evaluation of Titanium Dioxide as a Pharmaceutical Excipient for Preformulation of a Photo-Labile Drug : Effect of Physicochemical Properties on the Photostability of Solid-State Nisoldipine

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To characterize the photocatalytic activity of TiO_2 via solid-state reaction, the relationship between the physicochemical properties and photocatalytic activity of TiO_2 was investigated and estimated from the results of photodegradation of nisoldipine. The photodegradation of nisoldipine was significantly enhanced by addition of TiO_2. Two degradation products, nitroso-phenylpyridine derivative and nitro-phenylpyridine derivative, were formed. The degree of photocatalytic activity of TiO_2 was quite different between the various types of TiO_2 investigated, even when the crystalline phase was the same. As a result of the investigations into the relationship between the photocatalytic activity and physicochemical properties of TiO_2, it was found that for the rutile form the photocatalytic activity has good correlation with specific surface area of TiO_2, but poor correlation with water loss on drying of TiO_2. However, for the anatase form, the photocatalytic activity has good correlation with water loss on drying of TiO_2, but poor correlation with specific surface area. Moreover, it was found that the crystallinity of TiO_2 has a moderate correlation with the photocatalytic activity of both crystal forms of TiO_2. These results suggest that a degree of photocatalytic activity of TiO_2 depends on the various physicochemical properties of each type of TiO_2 investigated.
公益社団法人日本薬学会の論文
2005-07-01