A preliminary study of the stability of midazolam in polypropylene syringes

The physiochemical stability of midazolam stored in polypyropylene syringes was studied. Solutions containing approximately 3 mg/mL of midazolam were prepared by diluting commercial ampoules of the drug with sodium chloride 0.9% for injection. The solutions were stored at 20.degree.C, 32.degree.C (to simulate usage conditions), and 60.degree.C for 13 days, and the concentration of midazolam was periodically determined using a high performance liquid chromatography assay. The midazolam solutions were reasonably stable, with all solutions maintaining over 90% of their initial chemical potency for at least one week. There were no evident changes in the physical appearance or pH values of the solutions over the couse of the study. The presence of morphine tartrate seemed to slow the degradation of midazolam, possibly by increasing the pH of the solution. There was no significant uptake of midazolam into the syringe. The clinical implication of these results is that, on the basis of physicocochemical stability, syringes of midazolam (with or without morphine) need only be changed at intervals of up to one week in palliative care patients receiving the drug via a portable subcutaneous infusion device.