The objective of this study is to
clarify the mechanism of extending
release of highly water-soluble drugs via counter polymer (CP) utilization
in poly(ethylene oxide) (PEO)/polyethylene glycol (PEG) matrix tablets.
Carbomer, poly(acrylic acid), was used as a CP, which has the opposite
charges to the drugs. The in vitro release of several highly water-soluble
drugs from PEO/PEG tablet with or without CP were tested, the relationship
between the sustained release effect by a CP (SRE) and the physicochemical
properties of the drugs was investigated. The results demonstrated
that the utilization of CP can extend the release of some highly water-soluble
drugs by effectively controlling the drug diffusion through matrices.
On the other hand, the effectiveness of CP was different depending
on the drugs applied. There were not statistical correlations between
SRE and physicochemical properties such as solubility, molecular weight,
and charge intensity of the drugs, while a micelle forming property
of the drugs played an important role in SRE by CP. It was concluded
that CP, Carbomer, having negative charges could effectively interact
with opposite charges on the surface of stable drug micelles, which
could result in a significant decrease in drug diffusion leading to
extended drug release. It is considered that the system utilizing
CP is a promising approach to achieve extended release of highly water-soluble
drugs with a reasonable tablet size, especially in the case of large
drug loading.