K. Tahara et al., OVERALL MECHANISM BEHIND MATRIX SUSTAINED-RELEASE (SR) TABLETS PREPARED WITH HYDROXYPROPYL METHYLCELLULOSE-2910, Journal of controlled release, 35(1), 1995, pp. 59-66
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.