Pharmaceutical evaluation of magnesium oxide fine granule formulation for conversion to magnesium hydroxide owing to humidification by near-infrared spectroscopy

In this study, we evaluated the changes in near-infrared (NIR) spectra of heavy MgO (100 % MgO; H_MgO) fine granules formulations when stored under humidified conditions. The H_MgO formulations are often mixed with other powdered formulations in clinical practice. In all H_MgO formulations, the peaks at approximately 7350 cm⁻¹ and 7150 cm⁻¹ increased, whereas the peak at approximately 7300 cm⁻¹ decreased depending on the storage period under humidified conditions. Furthermore, slight enhancement of the peaks around 7250 cm⁻¹ and 7200 cm⁻¹ was also observed. These peak changes are attributed to the three-dimensional structure of magnesium hydroxide (Mg(OH)₂) produced by humidification. Subsequently, we evaluated the changes in the NIR spectrum of H_MgO after mixing with 10 % water. The time required for the peak change to appear was shorter than that for storage under humidified conditions. Furthermore, the peaks around 7350 cm⁻¹ , 7250 cm⁻¹ , and 7150 cm⁻¹ were clearly enhanced, and the peak around 7300 cm⁻¹ disappeared immediately after the addition of water. These results suggest that although Mg(OH)₂ is produced when H_MgO is mixed with water, the rate and mechanism of production differ from those observed under humidified storage. The presence of Mg(OH)₂ generated by humidified storage or by mixing with water may affect the stability and water solubility of concomitant pharmaceutical formulations that are sensitive to an alkaline environment. The findings of this study provide useful insights from both fundamental and medical perspectives, and they suggest that NIR spectroscopy, which allows rapid and non-destructive measurements, is effective for these evaluations.