Stability and dissolution of lozenge and emulsion formulations of metronidazole benzoate

Chicken flavored glycerinated gelatin candy-based lozenges and oil-in-water emulsions of metronidazole benzoate were prepared for veterinary use. The stability and dissolution of the lozenges and emulsions were investigated via a high-pressure (performance) liquid chromatography (HPLC) assay. The separation and quantitation of metronidazole benzoate were achieved on a Phenomenex IB-SIL 5 C8 column (250 x 4.6 mm,id) at ambient temperature, with a 55:45 v/v pH 7.0 phosphate buffer-acetonitrile mobile phase at a flow rate of 1.0 mL/min. Tinidazole was used as the internal standard. A sample of metronidazole benzoate form the lozenge and emulsion was prepared for assay by dissolving one lozenge or 1g of the emulsion in 50:50 v/v methanol-water solution, and that sample was filtered through a 0.2 micrometer membrane filter before assay. The chromatogram was monitored with ultraviolet detection at 230 nm. The HPLC separation of metronidazole benzoate was achieved in less than 10 minutes; sensitivity was in the rage of 10 ng/mL. This method can be used to separate metronidazole and benzoic acid, which are degradation products of metronidazole benzoate, and demonstrated linearity for metronidazole benzoate in the range of 0.01 to 100 micrograms/mL. Accuracy and precision were less than 1.0% and less than 0.54%, repectively. The limit of quantitation was 10 ng/mL, and the limit of detection was 0.01 ng/mL, based on a signal-to-noise ratio of 3 and a 20 microliter injection. The recoveries of metronidazole benzoate from the lozenge and emulsion were 98% +/- 4% and 99% +/- 2%, respectively. Stability testing of the new formulations was performed at ambient temperature and at 4 deg C. Dissolution testing used the USP paddle method at 37 deg C and 100 rpm in simulated gastric fluid without pepsin. Both formulations were stable at ambient temperature and at 4 deg C. Metronidazole benzoate is completely released from the lozenge and emulsion formulations based on dissolution T50% values of 4.2 and 24 minutes and T90% values of 12.8 and 83 minutes, repectively.