Abstract: A coating base for solid enteric pharmaceutical preparations having a dissolution pH ranging from 3.5 to 4.5 essentially consisting of hydroxypropylmethyl cellulose trimellitate obtained by substituting water-soluble hydroxypropylmethyl cellulose having 1.1 to 1.6 methoxy group per glucose ring thereof with 0.2 to 1.0 trimellitate group per glucose ring, or obtained by substituting water-soluble hydroxypropylmethyl cellulose having 1.7 to 2.1 methoxy groups per glucose ring thereof with 0.2 to 0.5 trimellitate group per glucose ring. The coating base can be dissolved at the upper portion of the small intestine without delay and a solid enteric pharmaceutical preparation provided with a coating film of the base can completely release the drug included therein before the preparation passes through the small intestine. Therefore, the base can ensure a high pharmacological action of the drug.

Abstract: The invention provides a novel method for providing entric coating on solid dosage forms using an aqueous coating liquid so that the problems inherent to the use of a coating liquid in an organic solvent can completely be eliminated. The inventive method comprises dispersing a finely divided powder of a hydroxypropylmethylcellulose phthalate in an aqueous medium containing triacetin to give an aqueous coating liquid with which the solid dosage forms are coated, for example, by spraying and dried. It is necessary that the preparation of the coating liquid and the coating procedure with the coating liquid are performed throughout while keeping the temperature of the liquid below 25.degree. C. so as that the particles of the hydroxypropylmethylcellulose phthalate are not dissolved in the medium forming a stable dispersion without adhesive coalescence.