Storage Stability of Hospital-Prepared Mianserin Suppositories: Evaluation of Residual Active Ingredient Content and Bacteriological Contamination under Different Storage Conditions

Background Mianserin suppositories are a hospital preparation usable for patients who cannot take oral medication. However, data on the stability of hospital preparations are limited. Therefore, this study investigated the stability of mianserin suppositories over time and the appropriate storage methods. Methods For the long-term chemical stability testing, five conditions were compared: RL; room temperature (15–30°C) under ambient light, RD; room temperature in the dark, CL; cool temperature (2–8°C) under ambient light, CD; cool temperature in the dark, and FD; frozen temperature (-20°C) in the dark. High-performance liquid chromatography (HPLC) was used to compare time-dependent component contents at 0, 2, 4, 8, 16, and 24 weeks (n = 5). Microbial limit tests for total aerobic microorganisms and fungi were conducted using the agar plate dilution method immediately after preparation and after 24 weeks in RL, and after 24 weeks at FD (n = 4). Results A gradual decline was observed under all storage conditions. The residual content rate (mean ± SE) after 24 weeks was as follows: RL, 96.2 ± 0.3%; RD, 96.2 ± 0.2%; CL, 97.0 ± 0.3%; CD, 97.3 ± 0.3%; and FD, 98.3 ± 0.2%. Under all conditions—immediately after preparation, after 24 weeks of RL, and after 24 weeks of FD—the total aerobic microbial count was ≤ 1000 CFU/g, and the total fungal count was ≤ 100 CFU/g. Conclusion The results showed that the residual content remained satisfactory from immediately after preparation through 24 weeks under all storage conditions, ranging from RL to FD.