Development of cellulose derivatives as novel enteric coating agents soluble at pH 3.5-4.5 and higher

Hydroxypropyl methylcellulose (HPMC) was selected as a base polymer to develop novel enteric coating agents for acid protection which can dissolve at pH around 4, and was modified with trimellitic acid or maleic acid at various degrees of substitution. These carboxylic acids have higher dissociation constants and higher solubility in water than the carboxylic acids of existing enteric coating polymers. The synthesized polymers were micronized and dispersed in aqueous medium to determine their pKa values by potentiometric titration. The pH of dissolution and the water vapor permeability of the cast films prepared from organic solutions were also evaluated. Hydroxypropyl methylcellulose trimellitate (HPMCT) showed good acid resistance, and the pH at which it dissolves can be controlled in the range of pH 3.5 to 4.5 by varying the content of trimellityl groups and the methoxyl substitution of the base polymer.