The stability of mixtures of morphine hydrochloride, bupivacaine hydrochloride, and clonidine hydrochloride in portable pump reservoirs for the management of chronic pain syndromes.

The physical and chemical stability of a combination of drugs commonly administered into the epidural or intrathecal space for the treatment of chronic pain was investigated. The concentrations of bupivacaine hydrochloride, morphine hydrochloride, and clonidine hydrochloride were measured using high performance liquid chromatography. The solutions were stored in reservoir bags for up to 90 days. No macroscopic or microbiological signs of precipitation, change in color, or contamination were observed, and pH remained stable. None of the three drugs declined in concentration during the observation period. A small increase in concentration of all three drugs did occur over time, most probably due to evaporation processes. In conclusion, no problems in physical or chemical stability are to be expected when combining morphine, bupivacaine, and/or clonidine for long-term epidural or intrathecal administration. In the case of clinically apparent loss of analgesic efficacy, other mechanisms should be considered.