Approaches to improve the stability of the antiviral agent UC781 in aqueous solutions

In this work, we evaluated the chemical stability profiles of UC781 based solutions to identify excipients that stabilize the microbicidal agent UC781. When different antioxidants were added to UC781 in sulfobutylether-β-cyclodextrin (SBE-β-CD) solutions and subjected to a 50 °C stability study, it was observed that EDTA was a better stabilizing agent than sodium metabisulfite, glutathione or ascorbic acid. Some antioxidants accelerated the degradation of UC781, suggesting metal-catalyzed degradation of UC781. Furthermore, we observed substantial degradation of UC781 when stored in 1% Tween 80 and 1% DMSO solutions alone or in those with 10 mM EDTA. On the other hand, improved stability of UC781 in the presence of 100 and 200 mM of EDTA was observed in these solutions. The addition of both EDTA and citric acid in the stock solutions resulted in recovery of more than 60% of UC781 after 12 weeks. Generally, 10% SBE-β-CD in the presence of EDTA and citric acid stabilized UC781 solutions: the amount of UC781 recovered approaching 95% after 12 weeks of storage at 40 °C. We also showed that the desulfuration reaction of the UC781 thioamide involves oxygen by running solution stability studies in deoxygenated media. Improved stability of UC781 in the present study indicates that the incorporation of EDTA, citric acid and SBE-β-CD and the removal of oxygen in formulations of this drug will aid in increasing the stability of UC781 where solutions of the drug are required.