Long-term stability of ready-to-use 1-mg/mL midazolam solution

Midazolam is a benzodiazepine derivative commonly used in intensive care units to control sedation. Its use requires dilution of a 5-mg/mL commercial solution to a target concentration of 1 mg/mL. A study was conducted to evaluate the stability of diluted ready-to-use 1-mg/mL midazolam solutions over 365 days when stored in cyclic olefin copolymer vials or polypropylene syringes.

A specific stability-indicating high-performance liquid chromatography coupled with UV detection method was developed for midazolam hydrochloride and validated for selectivity, linearity, sensitivity, precision, and accuracy. Three storage conditions were tested: -20°C ± 5°C, 5°C ± 3°C, and 25°C ± 2°C at 60% ± 5% relative humidity. Half of the vials were stored upside down to test for the absence of interaction between midazolam and the stopper. Particle contamination, sterility, and pH were assessed.

The limit of stability was set at 90% of the initial concentration. After 1 year's storage at -20°C and 5°C, concentrations remained superior to 90% under all storage conditions. At 25°C, stability was maintained up to day 90 in syringes (mean [SD], 92.71% [1.43%]) and to day 180 in upright and upside-down vials (92.12% [0.15%] and 91.57% [0.15%], respectively). No degradation products were apparent, no variations in pH values were detected, and containers retained their sterility and conformity with regard to any specific contamination during the study.

The evaluated 1-mg/mL midazolam solution was stable over a 1-year period when stored at a refrigerated (5°C) or frozen (-20°C) temperature in both vials and syringes; with storage at 25°C, the stability duration was lower. The preparation of ready-to-use midazolam solutions by a hospital pharmacy is compatible with clinical practice and could help to decrease risks inherent in dilution in care units.