OVERALL MECHANISM BEHIND MATRIX SUSTAINED-RELEASE (SR) TABLETS PREPARED WITH HYDROXYPROPYL METHYLCELLULOSE-2910

The mechanisms of sustained release (SR) from tablet matrices prepared with hydroxypropyl methylcellulose (HPMC) 2910 polymers were investig ated to define the conditions for selection of appropriate polymers fo r SR formulation development. It is well known that the two important parameters for the release of drug from tablet matrices are the infilt ration rate of medium into the matrix, for those drugs with reasonable aqueous solubility, and the erosion rate of the matrix system, for th ose drugs with poor aqueous solubility. In addition, the amount of dru g loaded into the tablet also influences the release rate of the drug. The infiltration rate of medium into the matrix can be controlled by changes in the interspace volume of the matrix by the use of higher le vels of materials such as lactose, which quickly rinse out of matrix s ystem. The larger interspace volumes produced by the higher ratio resu lt in more rapid release of the drug. The viscosity of HPMC polymers i s related to the molecular weight and has a large influence on the ero sion rate of matrix tablet. Use of a low viscous grade HPMC polymer is desirable for drugs that are poorly water soluble since the erosion r ate of the tablet matrix is the controlling factor for drug release. T he release rate of poorly soluble drug can be controlled by the rate o f tablet erosion. The tablet erosion rate can also be adjusted by the choice of HPMC polymer viscosity or by mixing HPMC of different viscos ity grades.