Stability of morphine sulfate in portable pump reservoirs during storage and simulated administration.

The stability of four concentrations of morphine sulfate injection in prefilled reservoirs for portable infusion pumps was studied after storage for 30 days at refrigerated and room temperature and after a three-day simulated administration period at body temperature. Thirty-milliliter samples of morphine sulfate injections in four concentrations--1, 5, 15, and 25 mg/mL--were loaded into a pump reservoir. The reservoirs were stored in the dark at 5 degrees C and 25 degrees C for 30 days. Samples were taken from each reservoir immediately after loading and after 7, 14, and 30 days of storage. The reservoirs were then connected to portable infusion pumps, which were run for three days at a flow rate of 0.4 mL/hr at 37 degrees C. The last sample was collected at the end of the three-day period. Samples were assayed for morphine sulfate content by high-performance liquid chromatography. The concentration of morphine sulfate increased up to 6% (for the 5-mg/mL sample) at refrigerated temperature and up to 16% (for the 15-mg/mL sample) at room temperature after 30 days' storage in the reservoirs. Evaporation of water from the reservoirs may have accounted for this phenomenon. No absolute relationship was found between the initial concentration of morphine sulfate and the percentage concentration increase after storage for 30 days. The change in morphine sulfate concentration before and after the three-day pumping period was not significant. Injectable solutions of morphine sulfate in concentrations ranging from 1 to 25 mg/mL are stable when stored at refrigerated temperature for 30 days in a prefilled drug reservoir.