Chemical Stability of Extemporaneously Prepared Lorazepam Suspension at Two Temperatures

The objective of this study was to determine the chemical stability of extemporaneously prepared lorazepam suspension (1 mg/mL) stored at two temperatures (4°C and 22°C) for 3 months. Lorazepam tablets marketed by two manufacturers (Mylan Pharmaceuticals and Watson Laboratories) were used to extemporaneously formulate two independently prepared suspensions. Each suspension was prepared using sterile water, Ora-Plus^® and Ora-Sweet^® to achieve a final concentration of 1 mg/mL. The two brands of tablets required different volumes of vehicles to prepare a pharmaceutically optimal suspension. The suspensions were stored in amber glass bottles at 4°C and 22°C for 91 days. Samples were analyzed by high performance liquid chromatography at baseline and on days 2, 3, 7, 14, 21, 28, 42, 63, and 91. The suspensions were considered stable if the mean lorazepam concentration remained greater than 90% of the initial concentration.

The chemical stabilities of these two extemporaneously prepared lorazepam suspensions were comparable throughout the study. Both lorazepam suspensions were stable for 63 days when stored at 4°C or 22°C, and both were stable for 91 days when refrigerated at 4°C. When stored at room temperature, the suspension prepared from the Watson tablet retained 88.9 ± 1.4% of the initial concentration on day 91 and was therefore considered unstable, while the suspension prepared from the Mylan tablet was stable for the entire 91-day study.