Photochemistry and Phototoxicity of Fluocinolone 16,17-Acetonide¶

Photochemical study of the highly used corticosteroids dexamethasone and prednisone. Effects of micellar confinement and cytotoxicity analysis of photoproducts

Photodegradation of dexamethasone (Dexa) and prednisone (Pred) occurs by a combination of ROS attack and unimolecular photodegradation reactions. The photoproducts obtained are more cytotoxic than the parent compounds.

Photostability of Topical Agents Applied to the Skin: A Review

Topical treatment modalities have multiple advantages starting with the convenient application and non-invasive treatment and ending with the reduction of the risk of the systemic side effects. Active pharmaceutical substances must reach the desired concentration at the target site in order to produce a particular therapeutic effect. In contrast to other dosage forms topical agents applied to the skin may also be susceptible to photodegradation after application. That is why the knowledge of the susceptibility of these topical drugs to UV irradiation, which may contribute to their degradation or changes in chemical structure, is very important. Active pharmaceutical substances used in dermatology may differ both in chemical structure and photostability. Furthermore, various factors-such as light intensity and wavelength, pH, temperature, concentration-can influence the photodegradation process, which is reflected in particular in kinetics of photodegradation of active pharmaceutical substances as well as both the quantitative and qualitative composition of by-products. The aim of this study was to conduct a systematic review of the photostability of dermatological drugs, as well as of other substances commonly applied topically. The photostability of glucocorticosteroids, retinoids, and antifungal drugs as well as non-steroidal anti-inflammatory drugs applied topically and selected UV-filters have been discussed. Furthermore, the impact of photoinstability on the effectiveness of pharmacotherapy and some photostabilization strategies have been also included.

Photodegradation of prednisolone under UVB solar irradiation. Role of photogenerated ROS in the degradation mechanism

The use of biologically active substances with anti-inflammatory properties such as corticosteroids has increased considerably in the last few decades. Particularly, the compound we are interested in, prednisolone (Predn), is a glucocorticoid with high biological activity. This compound absorbs UV radiation and may participate in photochemical processes, which can result in its own decomposition. These processes could result in the formation of free radicals or reactive oxygen species (ROS). On these grounds, the kinetic and mechanistic aspects of the direct photodegradation of Predn have been studied in aqueous medium under different atmospheric conditions by stationary and time-resolved techniques. The mechanism involved in the photodegradation has been elucidated. Predn is capable of generating the excited triplet state ³Predn* as a result of UVB light absorption. In the presence of oxygen, ³Predn* allows the formation of ROS, of which O₂(¹Δ_g) (Φ_Δ = 0.014), H₂O₂ and the radical OH˙ stand out. The latter is generated from the spontaneous dismutation of O₂˙^- and subsequent homolytic cleavage, photochemically promoted, of H₂O₂. Predn undergoes unimolecular photodegradation reactions under an inert argon atmosphere. In this study we found that in the presence of oxygen, the Predn photo-consumption is improved. This implies that the attack by ROS involves a very important additional contribution to the photodegradation of Predn under aerobic conditions.

Stability-indicating chromatographic determination of hydroquinone in combination with tretinoin and fluocinolone acetonide in pharmaceutical formulations with a photodegradation kinetic study

Stability indicating HPLC and TLC-densitometric methods for the determination of hydroquinone, tretinoin, fluocinolone acetonide, their degradation products and preservatives.

Photohemolysis Sensitized by the Furocoumarin Derivative Alloimperatorin and its Hydroperoxide Photooxidation Product

The dark and photosensitized effects of alloimperatorin methyl ether 1 (hereafter simply alloimperatorin) and its photooxygenation product alloimperatorin hydroperoxide 2 were investigated on human erythrocytes. The results reveal that the furocoumarin 1 photosensitizes efficiently the hemolysis of erythrocytes. The rate of photohemolysis increases on raising the temperature of the postirradiated incubation from 4°C to 37°C. Thermal activation of the photohemolysis and inhibition by 2,6-di-tert-butyl-p-cresol (BHT) suggest that the furocoumarin 1 photosensitizes lipid peroxidation, increasing permeability in the erythrocyte membrane. The hydroperoxide 2 induces dark and photosensitized hemolysis more efficiently than the furocoumarin 1. The rate of hemolysis induced by 2 increases with the incubation temperature and decreases in the presence of tert-butanol and BHT. The hydroperoxide 2 photosensitizes the formation of lipid peroxidation products as shown by the reaction with thiobarbituric acid. This process is diminished by BHT. Our data imply that the photohemolysis sensitized by the furocoumarin 1 is caused by the in situ-formed photooxygenation product 2. Such hydroperoxides are potent hemolytic agents in the dark and especially on photosensitization.