Hypromellose phthalate (HPMCP) is a type of pharmaceutical excipient that is used in the formulation of oral dosage forms, particularly in the production of enteric-coated tablets and capsules. It is derived from cellulose, which is a natural polymer that forms the structural component of plant cell walls. HPMCP is a water-soluble, anionic polymer that is commonly used as an enteric coating material due to its excellent film-forming properties, stability, and resistance to gastric fluids.
HPMCP was first introduced in the early 1970s and has since become a widely used enteric coating material due to its unique properties. It is produced by esterification of hypromellose with phthalic acid and is available in a range of different grades, depending on the degree of phthalation and the molecular weight of the polymer. The most commonly used grades of HPMCP are HPMCP-55, HPMCP-50, and HPMCP-HP-55, which have different degrees of phthalation and are suitable for use in different types of formulations.
The main function of HPMCP in pharmaceutical formulations is to protect the active ingredients of the drug from degradation in the acidic environment of the stomach. When a tablet or capsule containing HPMCP is ingested, the coating remains intact in the stomach due to the low pH, but once the dosage form reaches the more alkaline environment of the small intestine, the coating begins to dissolve and release the active ingredients. This delayed release helps to ensure that the drug is delivered to the site of action and that its efficacy is not compromised by gastric acid.