Stability of Two Concentrations of Morphine Tartrate in 10 mL Polypropylene Syringes

Objective: Analgesics are often given by subcutaneous infusions in palliative care. We studied the physical and chemical stability of two concentrations of morphine tartrate stored in 10 mL polypropylene syringes. Solutions containing 800 mg and 40 mg of morphine tartrate in 10 mL were prepared from commercially available ampoules and, where necessary, diluted to volume with 0.9% sodium chloride for injection. Method: The solutions were stored in the dark, at 21– 230C or 4–8°C for three weeks. At intervals of two to three days the concentration of morphine was measured in duplicate samples from each of three syringes using a stability‐indicating high performance liquid chromatographic (HPLC) assay. Physical compatibility was assessed visually. Results: At both storage temperatures, the test solutions retained greater than 90% of their initial concentrations of morphine tartrate throughout the study period. A slight straw colour developed in the 800 mg in 10 mL solution stored at 18–23°C. At neither storage temperatures did the pH of either solution vary by more than 0.2 from initial values. Conclusion: Morphine tartrate, in the formulations tested, is stable when stored at 21–23°C and 4–8°C in polypropylene syringes for three weeks.