A study on the chemical stability of cholesterol-lowering drugs in concomitant simple suspensions with magnesium oxide

Difficulty in taking solid medicines is a common issue particularly for the elderly because of a decline in swallowing function, also known as dysphagia. For patients with such a dysfunction, a simple suspension method, in which solid medicines are disintegrated and suspended using warm water, has been developed and widely used in Japanese clinical settings. However, there is little information on drug stability in the simple co-suspension of multiple formulations especially including acidic or alkaline ones. In this study, the chemical stability of typical cholesterol-lowering drugs was investigated in a simple co-suspension with alkaline magnesium oxide (MgO) which is frequently used as a laxative or antacid in Japan.A cholesterol-lowering drug (one tablet) was soaked with or without MgO in warm water (55°C), and the vessel was left at room temperature for 10 min or 5 h. The suspensions prepared were then analyzed by high-performance liquid chromatography. Degradation products were analyzed by nuclear magnetic resonance spectroscopy and mass spectrometry for the structural elucidation.In the simple co-suspension with MgO, no significant degradation was observed for atorvastatin or pravastatin, while a significant decrease of the recovery from the co-suspension was observed for rosuvastatin after 5 h. On the other hand, simvastatin and ezetimibe co-suspended with MgO were partially degraded to simvastatin acid and a pyran compound, respectively.A simple co-suspension with MgO is feasible for atorvastatin, pravastatin, and rosuvastatin, although the rosuvastatin tablet should not be left soaking for a long time. Further it is inadvisable to suspend simvastatin or ezetimibe together with MgO because of their partial degradation.