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  • 1
    ISSN: 1573-904X
    Keywords: fluocinolone acetonide stability ; pH dependence ; Arrhenius parameters ; steroid formulation ; acid–base catalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract We investigated the degradation of fluocinolone acetonide (FA) incorporated into an oil-in-water cream base. The study examined the influence of temperature (23 to 80°C) and cream pH (pH 2.3 to 6) on FA degradation rates. FA degradation followed pseudo-first-order kinetics and adhered to the Arrhenius expression over the entire temperature range investigated. At all temperatures, the pH strongly influenced the observed degradation rate constant (k obs) values, with rate minima observed near pH 4. The FA log(degradation rate)–pH profiles were consistent with a reaction mechanism requiring drug hydrolysis catalyzed by hydroxide and hydrogen ions. Taking into account both the temperature and the pH dependence of FA degradation permits calculating k obs values from the following equation: $$\begin{gathered} k_{{\text{obs}}} = \exp \left\{ {22.5 - \left( {17,200/RT} \right)} \right\} + \exp \left\{ {38.7 - \left( {22,200/RT} \right)} \right\} \times \left[ {H^ + } \right] \hfill \\ {\text{ + exp}}\left\{ {{\text{49}}{\text{.5}} - \left( {21,100/RT} \right)} \right\} \times \left[ {OH^ - } \right] \hfill \\ \end{gathered}$$ where the three bracketed terms represent Arrhenius expressions for neutral, acid-catalyzed, and base-catalyzed hydrolysis reactions. FA degradation in the cream base parallels the degradation of a related steroid (triamcinolone acetonide) in an aqueous alcohol solution. The equivalence between FA and triamcinolone acetonide kinetics in the different reaction media suggests that in the cream base, FA degradation is limited to an aqueous phase largely unperturbed by the presence of nonaqueous constituents that comprise the cream formulation.
    Type of Medium: Electronic Resource
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