Stability of morphine sulphate in saline under simulated patient administration conditions

To study the stability of morphine sulphate solutions under simulated administration conditions in a patient-controlled analgesic device.

Concentrations of 1 mg/ml and 10 mg/ml morphine sulphate in saline were monitored over 16 days under slow continuous delivery from Deltec Medication cassettes kept in the dark at a controlled temperature of 32 degrees C and a humidity between 36 and 38%. The morphine concentrations in the samples, collected at 0, 1, 2, 5, 6, 7, 9, 12, 14 and 16 days, were measured by a stability indicating high-performance liquid chromatographic method.

Throughout the study period, the reservoir concentrations varied within 10% of their initial values and there was no chromatographic evidence of degradation. However, the pH of both reservoirs decreased with time, but morphine is expected to be stable within the observed pH range.

This study demonstrated that the concentrating effect due to evaporation under the storage conditions described, over 16 days, was not of significance and the product was stable.