Stability of high-dose morphine chloride injection upon heat sterilization: comparison of UV-spectroscopy and HPLC

The stability of a preservative-free morphine chloride solution for intravenous or intrathecal use manufactured at a concentration of 40 mg/ml, near the solubility limit in water, was studied. The influence of heat and oxygen on morphine content was measured with and without autoclaving, and after additional thermal and oxidative stress. The morphine injection was stable during steam sterilization at 121 degrees C for up to 180 min if the solution was adjusted to a pH of 3.2 and if oxygen was eliminated by saturating the solution and flushing the vial with nitrogen before sealing. By adding an oxidizing agent (200 microliters H2O2 3% per 20 ml vial) before 15 min of sterilization, a decomposition of approximately 20% of morphine resulted when compared to oxygen-free control samples (P < 0.01, n = 3) High-performance liquid chromatography with UV detection (HPLC) and direct UV spectroscopy (UV) (the latter available in most hospital pharmacies for analytical purposes) were compared for specificity, precision and appropriateness for content and stability assessment of morphine solutions. UV could only be used for quantification of undecomposed morphine. Morphine degradation products of stressed solutions interfered with the direct UV assay of morphine at 286 nm, whereas these interfering components were separated by the ion-pair reversed-phase HPLC used. The results demonstrate that even in the absence of stabilizers, morphine chloride solutions may safely be sterilized for 15 min at 121 degrees C. The HPLC method was shown to be sufficiently sensitive and specific for quality control and stability assessment of morphine preparations, and, therefore, appropriate for the validation of the manufacture of morphine injection solutions in hospital pharmacies, where morphine solutions are manufactured in special strengths and volumes for individual patients' needs.