Background To extend the range of injectable preparations in a centralised intravenous admixture service (CIVAS).

Purpose To investigate the long term stability of morphine in 0.9% NaCl infusion polyolefin bags (PB) and polypropylene syringes (PS) after storage at 5±3°C, and to evaluate the influence of initial freezing and microwave thawing on this stability.

Materials and methods Ten PB and five PS containing 100 ml of 1 mg/ml of morphine solution in 0.9% NaCl were prepared under aseptic conditions. Five PB were frozen at -20°C for 90 days before storage. Immediately after the preparation and after thawing, 2 ml of each bag were withdrawn for the initial concentration measurements. All PB and PS bags were then refrigerated at 5± 3°C for 58 days during which the morphine concentrations were measured periodically by high performance liquid chromatography using a reversed phase column, naloxone as internal standard, a mobile phase consisting of 5% acetonitrile and 95% of KH₂PO₄ buffer (pH 3.50), and detection with diode array detector at 254 nm. Visual and microscopic observations, spectrophotometric and pH measurements were also performed. Solutions were considered stable if the concentration remains superior to 90% of the initial concentration by regression analysis. The degradation products peaks were not quantitatively significant and were resolved from the native drug.

Results PB and PS solutions were stable when stored at 5± 3°C during these 58 days. No colour change or precipitation in the solutions was observed. The physical stability was confirmed by microscopic and spectrophotometric inspection. There was no significant change in pH during storage. Freezing and microwave thawing didn't influence the infusion stability.

Conclusions Morphine infusions may be prepared in advance by CIVAS, frozen in PB and microwave thawed before storage under refrigeration until 58 days either in polyolefin bags or polypropylene syringes. Such treatment could improve safety and management.