Stability of Metronidazole Benzoate in SyrSpend SF One-Step Suspension System

The objective of this study was to determine the stability of metronidazole benzoate suspension in SyrSpend SF One-Step Suspension system. The studied samples were packaged in 60-mL amber plastic prescription bottles, which were stored protected from light under controlled environmental conditions for a period of 360 days. Stability of metronidazole benzoate suspension in SyrSpend SF was assessed based on retention of initial color or appearance, pH of suspension, and recovery of metronidazole benzoate from the packaged product. Duplicate samples were evaluated at each predefined time interval. An assay method by high performance liquid chromatography was validated for its specificity and stability-indicating characteristscs through a forced-degradation study, and was used in metronidazole benzoate assay. Metronidazole benzoate in SyrSpend SF retained its normal appearance of an opaque suspension, with acceptable pH values ranging from 4.43 to 4.53 (range 4.45 +/- 0.5). Recovery of metronidazole benzoate at subsequent time points was within 90% to 110% of inital concentration for samples stored at refrigerated temperature (2 deg C to 8 deg C), and ambient condition (25 deg C/60% relative humidity), with no detectable changes in chromatographic profile for most tested samples. The rates of change in potency for metronidazole benzoate were determined under the assumptions of first-order kinetics, and the time to reach 90% to 110% initial concentration was determined to be 366 days for samples in ambient storage, or 716 days for samples stored at refrigerated temperature. Metronidazole benzoate in SyrSpend SF, which was packaged in amber plastic prescription bottles, is stable for at least 1 year when stored protected from light at ambient condition (25 deg C/60% relative humidity). The shelf life for this product may be extended to 2 years when stored at refrigerated temperature.