Polyelectrolytes in Controlled Release Coatings, Matrices, and Binders

1 Polyelectrolytes in Controlled Release Coatings, Matrices and Binders 

Polyelectrolytes (most notably ionic cellulose derivatives and crosslinked polyacid powders) are also commonly used as matrices, binders and excipients in oral controlled release compositions. In these applications, the polyelectrolytes provide hydrophilicity and pH sensitivity to tablet dosage forms. Acidic polyelectrolytes dissociate and swell (or dissolve) at high pH values whereas basic polyelectrolytes (for instance, polyamines) become protonated and swell at low pH. In either case, swelling results in increased permeability [290], thereby allowing an incorporated drug to be released. 

Cellulose disintegrants have been studied as insoluble matrices for sustained release tablets. Anionically charged carboxymethyl cellulose (sodium salt) was found to be inferior to methyl cellulose and poly(vinyl pyrollidone) as a binding agent for oxyphenbutazone tablets [291], However sodium carboxymethyl cellulose has found application as a dispersing agent for ibuprofen microspheres 

Responsive polyelectrolyte hydrogels that have been used for controlled release systems include gels which are hydrophobic in their neutral state 

The release kinetics of polyelectrolyte-containing controlled release compositions were modeled by Ozturk et al. [331]. According to this analysis the drug release rate depends on intrinsic solubilities as well as pKa values of the drug and polymer. Explicit relationships between release rates and these factors were derived, resulting in successful predictions of experimental data. 

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