For the purpose of quality evaluation of commercially available magnesium oxide (MgO) tablets, we studied their acid neutralization and dissolution behaviors. The dissolution test was carried out by the paddle method in 1st ‰uid (pH 1.2). The dissolution amount of MgO from tablets was determined by chelatometric titration. The medium pH was periodically measured. The neutralization reaction in 750 ml of 1st ‰uid was markedly diŠerent between two kinds of commercial tablets. The pH of medium including Magmittablet reached 8.9 and the dissolution rate of MgO was 81.1 ％ after 20 min. Contrariwise, theˆnal pH of medium including Maglaxtablet was 2.5 and the dissolution rate of MgO was 77.1％ after 60 min. These results indicate that the dissolution rate of MgO from tablets should be ＞81.1％ to obtain signiˆcant acid neutralization action.

For the purpose of quality evaluation of magnesium oxide (MgO) tablets, we considered the dissolution test method with changes in the pH of the dissolution medium as an indicator and studied the elution behavior of MgO from commercial MgO tablets. We also studied the effects of particle size on the elution rate of MgO from MgO tablets. A dissolution test was carried out using the rotating basket method in 100 ml of the first fluid (pH 1.2). The stirring speed was set at 200 rpm. The elution behaviors of MgO from two products were markedly different. The medium pH for the sample MM (Magmit) tablet after 15 min reached 9.5 but that for ML (Maglax) tablet was 2.7 even after 60 min. The apparent solubility of MgO in 100 ml of the first fluid were, respectively, 175 mg and 100 mg when medium pH as 9.5 and 1.5. The low dissolution of ML tablets is thought to be due to the large particle size (average particle size r = 226 microm) or due to the effects of additives on elution. These results suggest that neutralizing activity after ingestion of MgO tablets and subsequent laxative effects may, when conditions after ingestion of MM tablets and after ingestion of ML tablets are compared, produce differences between them. We found that the dissolution test method with pH as an indicator is useful in assessing the dissolution behavior of MgO preparations.