Chemical stability of methadone concentrate and powder diluted in orange-flavored drink.

Methadone, traditionally used in the treatment of heroin addiction, recently has been used to treat severe pain. The chemical stability of methadone has been studied in concentrations up to 1.5 mg/mL only. Commercial methadone concentrate (10mg/mL) and methadone powder was diluted to 5 mg/mL with orange-flavored Tang drink. Sodium benzoate was added to the solutions prepared from powder. Bottles were stored at either room temperature (22 deg C) or under refrigeration (6 deg C) for 91 days. Samples were analyzed in duplicate by a stability-indicating high-performance liquid chromatographic assay, and clarity and pH were also monitored. One additional solution was preprared from powder but no preservative was added; this solution was monitored for presence of bacterial growth at room temperature only. Solutions prepared from the concentrate and powder with preservative showed no signs of change in clarity on storage. The solution made from powder only developed turbidity after 21 days, which suggested bacterial growth. There was no significant change in pH over the course of the study. After 91 days of storage at either room temperature or under refrigeration, there was no change in concentration for solutions prepared from concentrate or powder with preservative. Methadone solutions prepared from the commercial concentrate or powder with sodium benzoate are stable for 91 days at room temperature or under refrigeration. Solutions prepared from the powder but not containing a preservative showed signs of bacterial growth after 21 days at room temperature.