Change of the dosage form of the medicine is a useful method for the improvement of the medicine-taking compliance. However, the photostability of the medicine may be decreased on account of the change of the dosage form, followed by the change of the quality of it. On the other hand, there is few information focused on the photostability of the dosage-changed medicine. In this study, the effects of the change of the dosage form on the photostability of some non-steroidal anti-inflammatory drugs (NSAIDs) are investigated. Photo-exposure by means of the black light, containing ultraviolet (UV) at mainly 365 nm, induced the change of the color of naproxen tablets although the content of the active compound monitored by the high-performance liquid chromatography (HPLC) was not changed. However, the change of the dosage form of naproxen tablets to the powder and the suspension induced the change of the photostability followed by the decrease of the content of the active compound and the generation of two photoproducts. By means of the nuclear magnetic resonance (NMR) analysis, structures of two naproxen photoproducts were determined as 2-acetyl-6-methoxy-naphthalene and 1-(6-methoxy-2-naphthyl) ethanol. This is the first report evaluated the generation of naproxen photoproducts induced by the long-wavelength UV irradiation in the formulation.

A photostabilization strategy is an important aspect of quality assurance for photosensitive compounds. This study focused on the photoprotective effects of selected antioxidants including the effect of L-ascorbic acid (AA) on naproxen (NX) photodegradation in aqueous media. NX degradation during ultraviolet light (UV) irradiation and the protective effects of selected antioxidants were monitored by high-performance liquid chromatography (HPLC). The addition of AA induced the suppression of NX photodegradation, although the protective effect disappeared after AA was degraded completely. The results of the evaluations on the photoprotective effects on NX photodegradation and antioxidative activities of AA and other antioxidants showed that the protective effects of antioxidants are dependent on reducing power and photostability under UV irradiation. In this experiment, quercetin (QU) is the most effective antioxidant on account of the residual rate of QU after UV irradiation and the antioxidative activity in the potential antioxidant (PAO) test was significantly higher compared to other antioxidants following the higher protective effect on NX photodegradation.