Cellulose derivative for enteric coating
Since the introduction of HPMCP (hypromellose phthalate USP/NF, JP, EP) in 1971, it has proved its value in enteric coating using organic solvent. The chemical structure of HPMCP is a monophthalic acid ester of hypromellose.
The threshold pH value for rapid disintegration of HPMCP can be controlled by varying the phthalyl content. Two types of HPMCP with different in pH-solubilities, HP-55 and HP-50, are available. Moreover, HP-55S, a special type of HP-55, which is distinguished by its higher molecular weight, greater film strength and higher acid resistance properties, has also been introduced. A suitable grade of HPMCP for a particular purpose should be selected in accordance with each preparation.