Compatibility and stability of fentanyl admixtures in polypropylene syringes

Objective: To determine the physicochemical stability of fentanyl in combination with midazolam and either hyoscine butylbromide or metoclo- pramide, and stored in 30 ml polypropylene syringes. Methods: Solutions containing approximately 40 μg/ml of fentanyl in combination with midazolam (approximately 600 μg/ml) and either metoclopramide (approximately 700 μg/l) or hyoscine (approximately 850 μg/ml) were prepared from commercial ampoules of the drugs. The solutions were stored, in triplicate, in the dark at 32 °C (to simulate usage conditions) for 10 days, and the concentration of each constituent drug was periodically determined using a stability-indicating high-performance liquid chromatography assay. Results: The combinations were relatively stable, with all drugs maintaining over 90% of their initial chemical potency for at least 1 week. There were no evident changes in either the physical appearance or pH values of the solutions over the course of the study. Conclusions: On the basis of physicochemical stability, polypropylene syringes containing fentanyl with midazolam and either hyoscine butylbromide or metoclopramide can be safely prepared and stored at or below 32 °C for periods of up to 1 week prior to use by palliative care patients receiving the drugs via a portable subcutaneous infusion device.