HPMC (hydroxy propyl methyl cellulose) is a partly o-methylated and o-(2-hydroxyl propylated) cellulose, obtained by treating alkali cellulose with chloromethane and propylene oxide. It is odorless and tasteless granular or fibrous powder which is creamy white or white in color. HPMC is soluble in cold water. Aqueous dispersions are prepared by dispersing material in about 25% hot water (80 °C) under vigorous stirring. On complete hydration of HPMC, a sufficient quantity of cold water is added and mixed. The gel point of HPMC dispersions varies from 50 °C to 90 °C. Gels are stable over a wide pH range. The viscosity of HPMC dispersions depends on the concentration of material used, its molecular weight, vehicle composition, presence of preservatives, and so on. Viscous gels can be prepared using high concentrations of high-molecular-weight grades. Inclusion of organic solvents, such as ethanol or viscosity, can be altered upon the blending of the components. A blending formula is available which is a very useful tool for determine the viscosity of the final HPMC preparation that we want to produce. The viscosity of a blend can, however, be approximated by use of the equation below, which is derived from the Arrhenius equation that relates viscosity with polymer concentration.viscoelastic, non-ionic hydrophilic polymer which is used extensively in various formulations of controlled release dosage form, as well as in ophthalmic preparations as lubricants. HPMC exhibits pH independent drug release profile. Extensive use of HPMC in controlled drug delivery system has been realized because they offer unique properties so far not been attained by any other polymers. The rate of the drug release from a matrix product depends on the relaxation of the polymer chains, which overall displays sustained release characteristics .
HPMC produces an elastic and tough coating which is highly consistent, economical, printable, non-allergenic, non-calorigenic, micro structural and are more resistant to microbial attack. With the use of HPMC not only controlled released dosage form are prepared but tablets with minimum efficacy (drugs showing tailored drug release profile) and optimum speed can be manufactured. The research about using HPMC in the controlled released dosage form is going on for about four decades. This is because, when HPMC is used as a polymeric matrix for the controlled released dosage form, the release of the drug takes place at a steady state rather than the controlled released dosage form which has been coated with normal coating ingredient. This results in uniform drug release with very lower chances of adverse effects like dose dumping.
Benefits of Using HPMC in the Controlled Release Dosage Form
Consumer Acceptance With the proper use of plasticizers, application rates, polymer concentration and application method excellent finishing of the product can be achieved. They can form a clear, sharp coatings and compatible with various dyes, colors and pigments that are approved by the FD&C. Hence consumer acceptance of tablets coated with HPMC increases. In case of HPMC, a clear cut of quality effective image can be obtained which shows that the tablets coated with HPMC easy swells up in the target site and shows desired mechanism of action.
Versatility HPMC is versatile in nature because it has a wide range of viscosities, grades and classes . According to the type of the product that is required, the viscosity grades can be substituted with each other to get the desired coating solution. The coating solution can be prepared in such a way that the solution can be optimized keeping other parameters constant.
HPMC is used as coating polymer, as well as matrix former in various drug deliveries. Due to its gel forming nature, it can be well accepted in controlled release drug delivery. The addition of ionic polymers to HPMC increases its drug release profile. It is light in weight hence it can be easily used to form gastro retentive drug delivery specially in floating drug delivery. Hence it can be stated that it has versatile uses in drug delivery.