Developing an injectable formula containing an oxygen-sensitive drug: a case study of danofloxacin injectable

The purpose of this study was to assess the impact of impurities in formulation components, antioxidants, formulation pH, and processing/packaging on the extent of color change associated with oxidation of danofloxacin injectable. The methods used in this study include reversed-phase HPLC, UV-VIS spectrophotometry, atomic absorption spectroscopy, visual observation, and iodimetric titration for quantification of the antioxidant. The results from this study revealed that trace impurities from two different excipients significantly contributed to color change associated with oxidation. Polyvinyl pyrrolidone (PVP) introduced trace levels of peroxides into the solution. A second excipient also had a significant impact on stability because it introduced trace metal impurities into the product. The minimization of oxygen levels alone in the solution and headspace was not sufficient to completely eliminate the product instability. The addition of an antioxidant, monothioglycerol (MTG), resulted in a formulation less sensitive to processing variables. The impact of pH on the performance of MTG was also studied. At pH 7.5, MTG resulted in significant improvement in stability; however, at pH 6.0 it was not effective as an antioxidant. Process modifications alone may not be sufficient to prevent oxidation. Chemical approaches, such as pH control, addition of an antioxidant, and control of components should be considered first as means of enhancing stability of oxygen-sensitive solutions.