Background Local anaesthetics and opioid mixtures are commonly used for the management of postoperative pain. The purpose of this study was to investigate the stability of butorphanol tartrate and ropivacaine hydrochloride in polyolefin bags over a period of 15 days, both at room temperature and at 4°C.

Methods Admixtures were assessed initially and for 15 days after preparation in polyolefin bags using 0.9% sodium chloride injection as diluents and stored at 4°C and 25°C. The initial concentrations were 50 μg/mL butorphanol and 1–2 mg/mL ropivacaine. The stabilities were determined by visual inspection, pH measurement and high-pressure liquid chromatography assay of drug concentrations.

Results The initial concentrations of butorphanol and ropivacaine were >97% after 15 days. The drug mixtures were clear in appearance and no colour change or precipitation was observed. Throughout this period, the pH value remained stable.

Conclusions Butorphanol and ropivacaine in 0.9% sodium chloride injection are stable for at least 15 days when stored in polyolefin bags at 4°C and 25°C.