Study on the chemical stability of β-lactam antibiotics in concomitant simple suspensions with magnesium oxide

A simple suspension method, where solid formulations are disintegrated and suspended by being soaked in warm water followed by tube administration, is widely used, especially for elderly patients with dysphagia in Japanese clinical settings. However, there is insufficient information on drug stability in the simple co-suspension of multiple formulations especially including acidic or alkaline ones. The influence of occasional prolonged soakage on drug stability is also of concern. In this study, the chemical stability of typical β-lactam antibiotics, amoxicillin, and cefcapene pivoxil hydrochloride, was investigated in simple co-suspensions with magnesium oxide (MgO), which is frequently used as an alkaline laxative for the elderly.

Amoxicillin (capsule) or cefcapene pivoxil hydrochloride (tablet) was placed with or without MgO (tablet) in a centrifuge tube containing warm water (55 °C). The tube was allowed to stand for 10 min or 5 h at room temperature and simple suspensions were prepared. The suspensions were then treated with large amounts of solvents and neutralized using a weakly acidic cation exchange resin. The resulting solutions were analyzed by high-performance liquid chromatography. The degradation products were identified by mass spectrometry and nuclear magnetic resonance spectroscopy.

Amoxicillin was found to be partially degraded to amoxicilloic acid and amoxicillin diketopiperazine by the co-suspension with MgO. The degree of degradation increased with the prolonged soaking. The recovery rates of cefcapene pivoxil decreased due to the poor solubility in the co-suspensions with MgO and no degradation product of the drug was observed.

Amoxicillin and MgO should be independently suspended because of the chemical instability of amoxicillin. This study has also indicated there is a degradation risk after prolonged soaking. It should be noted that the poor water solubility of cefcapene pivoxil under alkaline conditions may affect the absorption process as well as tube passability.