Stability of metronidazole free-base oral suspensions formulated with United States Pharmacopeia-grade metronidazole powder and commercial metronidazole tablets

This study reports on the stability of United States Pharmacopeia-grade metronidazole powder and commercially available metronidazole tablets in two dye-free oral suspending vehicles, namely Oral Mix and Oral Mix Sugar-Free. Metronidazole at 50 mg/mL was prepared individually in Oral Mix and Oral Mix Sugar-Free suspension vehicles and placed in 50-mL amber polyethyleneterephthalate bottles and 3-mL amber plastic syringes and stored at 4°C or 25°C/60% relative humidity for 90 days. The solutions were analyzed at the time of preparation and at 7 days, 14 days, 30 days, 45 days, 60 days, 75 days, and 90 days, with the concentration of metronidazole measured by high-performance liquid chromatography with photodiode array detection. The oral solutions were also monitored for pH, homogeneity, color, and odor. Except for the Oral Mix suspension of metronidazole prepared from the United States Pharmacopeia-grade powder and from the commercial tablet, when stored in pre-filled syringes, all the other preparations were stable at 4°C or 25°C/60% relative humidity for 90 days, with the metronidazole remaining within ± 10% of the initial concentration. The pH, color, odor, and resuspendability remained essentially unchanged. Metronidazole in Oral Mix and Oral Mix Sugar-Free oral suspensions, compounded from United States Pharmacopeia-grade powder or commercially available tablets, are a suitable alternative as an extemporaneously prepared medication.