As a phenothiazine derivative, Promethazine may undergo structural modifications when it is exposed to light. This process consists in the degradation of the initial compound and in the generation of new photoproducts with possible anti-infectious qualities. Stability studies are necessary in order to establish the proper use of drug solutions in different applications. At the same time, these investigations are important in the context of the generation of side-products induced by environmental conditions that bring new benefits to the compound.
This study reports the stability of Promethazine aqueous solutions, based on their absorption spectra acquired before and after Nd:YAG laser irradiation sessions or under different temperature and illuminating storage conditions. Samples of Promethazine solutions in ultrapure water, at a concentration range between 10-6 M – 10-2 M, were kept in dark at 22°C, and 4°C as well as at 22°C in ambient light up to a time interval of three months. Absorption spectra were recorded periodically in order to determine any changes of the optical properties. Also, solutions of 20 mg/mL were exposed for different time intervals to laser radiation emitted at 266 nm by the Nd:YAG laser. The stability of the optical properties of irradiated Promethazine solutions for 4 h was investigated up to two months.
The laser irradiated samples show similar but more rapid and intense changes compared to solutions exposed to ambient light, suggesting molecular modifications that could be due to the production of more polar phenothiazine derivatives.
The study reports an investigation of the photoproducts obtained by exposure of chlorpromazine hydrochloride in ultrapure water (concentration 2 mg/mL) to a 266-nm laser beam obtained by fourth harmonic generation from a Nd:YAG laser (6-ns full time width at half maximum, 10-Hz pulse repetition rate). The photoproducts were analyzed by steady-state UV-Vis absorption, laser-induced fluorescence, Fourier transform infrared spectroscopy, and liquid chromatography–tandem time-of-flight mass spectroscopy. Two figures showing pathways that take place during irradiation for obtaining the final products are shown. The quantum yield of singlet oxygen generation by chlorpromazine (CPZ) was determined relative to standard Zn-phthalocyanine in dimethyl sulfoxide. To outline the role of fluorescence in photoproducts formation rates, fluorescence quantum yield of CPZ during exposure to 355-nm radiation (third harmonic of the fundamental beam of Nd:YAG laser) was investigated relative to standard Coumarin 1 in ethanol. The CPZ solutions exposed 60 and 240 min to 266-nm laser beam, respectively, were tested against Staphylococcus aureus ATCC 25923 strain. For 25 μL of CPZ samples irradiated 240 min, a higher diameter of inhibition has obtained against the tested strain than for the 60-min exposed ones.
Phenothiazine exposed to white light or UV radiation undergoes a variety of reactions that result in the degradation of the parental compound and the formation of new species. Chlorpromazine exposed to the 266 nm laser beam of given energy levels yielded species derived from it, whose number increased with the exposure duration. At distinct time intervals the irradiation products were evaluated by spectrophotometry between 200-1500 nm, Thin Layer Chromatography, and for antimicrobial activity of Chlorpromazine against different test organisms such as Staphylococcus aureus.
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