The stability of OPALMON^® tablets, which contain the active ingredient Limaprostalfadex, a PGE₁ derivative, is known to be affected by humidity. In this study, we sought to investigate methods to improve the stability of OPALMON^® tablets under humid conditions. Polysaccharide additives, such as dextran, exhibited a stabilizing effect under humid conditions, while disaccharide additives, such as lactose, had no effect. Under humid conditions, the lyophilized drug product containing a disaccharide additive was liquefied. In contrast, the appearance of the product containing dextran was unchanged. Dextran and dextrin provided the best stabilization of this drug product in comparison with other saccharide and cellulose additives.

The pH of the lyophilized product mixed with various additives did not affect stability, regardless of the additives used. The moisture content of the product containing dextran or dextrin was higher than that of the product mixed with other additives, suggesting that the moisture content of the lyophilized product does not affect the stability of Limaprost-alfadex. Therefore, the mechanism of stabilization by dextran and dextrin remains to be elucidated. Differences in the mobility of water molecules between dextran and dextrin and other additives are likely to play a role in the stabilization of Limaprost-alfadex.