Stability of neostigmine methylsulfate injection at ambient temperature and 4 deg C in polypropylene syringes.

The stability of 1.0-mg/mL neostigmine methylsulfate injection in 6-mL polypropylene syringes stored at ambient temperature under continuous fluorescent light and at 4 deg C for up to 90 days was investigated. Concentration levels of neostigmine methylsulfate injection were determined at 0, 1, 4, 7, 15, 30, 45, 60, and 90 days after preparation of the syringes by means of a high-performance liquid chromatographic stability-indicating assay. Phenol, which was present as a preservative in the injection, did not interfere with the assay. The injections in plastic syringes were stable for up to 90 days at both ambient temperature and at 4 deg C. The pH of neostigmine methylsulfate injection did not change appreciable over the 90-day study period. These data support the stability of neostigmine methylsulfate injection under the storage conditions investigated in this study.