Stability of metronidazole in solutions and suspensions

Excellent stable oral liquid dosage forms of metronidazole can be prepared from tablets or powder using commercially available vehicle containing suspending agents. Liquid dosage forms (5 mg/ml) can be prepared without suspending agents. The four samples prepared (10 and 5 mg/ml) were stable for at least 90 days at room temperature. Their pH values and physical appearances did not change on storage. When metronidazole free base is prescribed it may not be substituted with the ester (metronidazole benzoate) as is common practice in the U.S.A. Metronidazole tablets with a labelled expired date of April 1986 still showed 99.3% potency when assayed in January 1993.