Butorphanol and ketamine combined in infusion solutions for patient-controlled analgesia administration: a long-term stability study.

Background: Ketamine in subanesthetic dose added to butorphanol has been reported to give superior pain control when used for intravenous patient-controlled analgesia (PCA) after surgery. However, this admixture is not available commercially and stability data applicable to hospital practice are limited.

Material/methods: The butorphanol-ketamine admixtures were prepared in polyolefin bags and stored in the dark at 4°C, 25°C, or 37°C for 15 days. The initial concentrations were 50-150 microgram/ml for butorphanol and 1-4 mg/ml for ketamine, respectively. The stabilities were determined by visual inspection, pH measurement, and high-pressure liquid chromatography (HPLC) assay of drug concentrations.

Results: Over the 15 days, all solutions were clear in appearance, and no color change or precipitation was observed among the three temperatures. The percentages of initial concentration of each drug were over 95% during the study period, and the pH value did not change significantly.

Conclusions: The results indicate that the drug mixtures of butorphanol and ketamine in 0.9% sodium chloride injection were stable for 15 days when stored in polyolefin bags at 4°C, 25°C, or 37°C.