e pH at which it dissolves in aqueous medium. HPMCP (also known as Hypromellose phthalate) [133] is commonly used in oral pharmaceutical formulations as an enteric coating material for tablets or granules [134-138]. Hypromellose phthalate is insoluble in gastric fluid, but will swell and dissolve speedily in the upper intestine. These polymers can be used as coating agents because they do not necessitate the addition of plasticizer or other film formers to fabricate coatings for oral formulations [128]. Hydroxypropyl methylcellulose phthalate (HPMCP), available in the market since 1971, it is a monophthalic acid ester of hypromellose, containing methoxy (-OCH3), 2-hydroxypropoxy (- OCH 2CHOHCH3) and phthaloyl (o-carboxybenzoyl C8H5O3) groups so, HPMCP is a cellulose in which some of the hydroxyl groups are replaced with methyl ethers, 2-hydroxy propyl ethers, or phthalyl esters. Numerous different types of hypromellose phthalate are commercially presented with molecular weights in the range 20 000–200 000. Typical average values are 80000–130000 [133]. These types are (HP50, HP55 and HP55S) where HP55 grade is usually used for enteric coating, HP55S grade, because of its higher degree of polymerization compared with HP-55, it have greater solution viscosity, greater mechanical strength of the film and HP-50 dissolves at a lower pH value and is therefore appropriate for preparations which are designed to disintegrate in the upper part of the small intestine.>