title: Photodegradation and stabilization of betamethasone-17 valerate in aqueous/organic solvents and topical formulations.
abstract: The effects of solvent [acetonitrile, methanol, and acetonitrile/water mixture (20:80, v/v)], buffer concentration (phosphate buffer, pH 7.5), ionic strength and commonly employed adjuvants on the photodegradation of betamethasone-17 valerate in cream and gel formulations have been studied on exposure to UV light (300-400 nm). A validated high-performance liquid chromatography method has been used to determine the parent compound and its photodegraded products. The photodegradation data in the studied solvents showed greater decomposition of the drug in solvents with a lower dielectric constant. A comparatively higher rate of photodegradation was observed in the cream formulation compared to that for the gel formulation. The kinetic treatment of the photodegradation data revealed that the degradation of the drug follows first-order kinetics and the apparent first-order rate constants for the photodegradation reactions, in the media studied, range from 1.62 to 11.30×10(-3) min(-1). The values of the rate constants decrease with increasing phosphate concentration and ionic strength which could be due to the deactivation of the excited state and radical quenching. The second-order rate constant (k') for the phosphate ion-inhibited reactions at pH 7.5 has been found to be 5.22×10(-2) M(-1) s(-1). An effective photostabilization of the drug has been achieved in cream and gel formulations with titanium dioxide (33.5-42.5%), vanillin (21.6-28.7%), and butyl hydroxytoluene (18.2-21.6%).
authors.affiliation: Faculty of Pharmacy, Hamdard University, Shahra-e-Madinat Al-Hikmah, Muhammad Bin Qasim Avenue, Karachi, 74600, Pakistan.
authors.forename: Saif-ur-Rehman
authors.initials: SU
authors.lastname: Khattak
authors.forename: Dilnawaz
authors.initials: D
authors.lastname: Shaikh
authors.forename: Iqbal
authors.initials: I
authors.lastname: Ahmad
authors.forename: Khan
authors.initials: K
authors.lastname: Usmanghani
authors.forename: Muhammad Ali
authors.initials: MA
authors.lastname: Sheraz
authors.forename: Sofia
authors.initials: S
authors.lastname: Ahmed
mesh_terms: D000287:Administration, Topical; D000893:Anti-Inflammatory Agents / Q000008:administration & dosage / Q000737:chemistry*; D001624:Betamethasone Valerate / Q000008:administration & dosage / Q000737:chemistry*; D004304:Dosage Forms; D007700:Kinetics; D009994:Osmolar Concentration; D055668:Photochemical Processes; D012997:Solvents / Q000737:chemistry*
chemical_list: D000893:Anti-Inflammatory Agents; D004304:Dosage Forms; D012997:Solvents; D001624:Betamethasone Valerate