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Zileuton (ABT-077) is a 5-lipoxygenase inhibitor with poor aqueous solubility. Using an extreme vertices experimental design and an empirical response surface analysis, both the solubility and pseudo-first-order degradation rate constants of zileuton were determined in a ternary solvent system consisting of water, ethanol and propylene glycol. The logarithm of the solubility increased curvilinearly with increasing weight fraction ethanol or weight fraction propylene glycol in the solvent system and decreased linearly with increasing dielectric constant of the medium. The degradation rate increased linearly with increasing weight fraction ethanol or weight fraction propylene glycol and the logarithm of the degradation rate constant increased linearly with respect to the reciprocal of the dielectric constant of the medium. The degradation products observed were the hydroxylamine, syn - and anti -oximes of zileuton, implying that a solvolysis reaction at the amide bond occurs in all solvent compositions. |
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