[Effect of storage temperature on gelation of oral methylcellulose formulation]

Heating a methylcellulose solution forms a thermal-reversible hydrogel. After the hydrogel forms, its properties change according to its temperature. However, the effects of heating this solution during storage and then cooling it are unclear. We investigated the effects of this heating and cooling on rheological and drug release characteristics. We prepared samples of methylcellulose solution (2% methylcellulose and 20% D-sorbitol) and examined them under two conditions: 1) storage for 24 hours at 4 to 30℃, 2) storage for 24 hours at 4 to 50℃, then cooling to 4℃ and maintained for 4 hours. We performed rheological investigations of viscosity, gelation temperature and gel strength, and examined the drug release characteristics by using a diffusion cell method with acetaminophen as the model drug. It was found that as the storage temperature rose, the methylcellulose solution increased in viscosity and the gelation temperature and gel strength changed. During storage at 30℃, the amount of drug released by the solution increased and the diffusion coefficient was high. When cooled to 4℃, the solution recovered its viscosity, gelation temperature, gel strength and drug release characteristics, regardless of the previous storage temperature. These results clarify that although the rheological and drug release characteristics of methylcellulose solution change with changes in storage temperature, the original characteristics are recovered after the solution is cooled to 4℃ and maintained at that temperature for four hours.