RHEOLOGICAL BEHAVIOR OF HYDROPHILIC POLYMERS AND DRUG RELEASE FROM ERODIBLE MATRICES

In order to provide a better understanding of the relevance of polymer viscosity to drug release from hydrophilic matrices, differing viscosity grades of two polymers (hydroxypropylmethylcellulose and sodium carboxymethylcellulose) were considered either alone or blended in differing proportions. The polymers and their blends were used to prepare heterogeneous matrices containing salbutamol sulfate as water-soluble model drug. Where evidence of erosion occurred, markedly differing release profiles were obtained depending on polymer viscosity. The same polymers were thoroughly characterized for their rheological behaviour, as a function of both shear rate and polymer concentration. A few rheological parameters were then calculated and their relationship with drug release was investigated. It was concluded that those parameters that are related to gel structure allow an explanation of the behaviour of the systems considered.