Knowledge of the release kinetics together with its (mathematical) model is inevitable for prediction of properties and optimization of dosage forms. The ability to optimize the release kinetics is a key factor in the endeavour of increasing pharmaceutical availability. The optimization may be done by a suitable choice of the dosage form or by clever distribution of the drug in the auxiliary substances or even by using an automatically working drug delivery device. This paper describes a model-based analysis and preparation of hydrogels. The following composition was used in the experiment: Chitosan – the gel creating basis; polymer, chlorhexidine – the drug; dodecyltrimethylammonium bromide – the auxiliary substance and surfactant. The release kinetics were studied at three temperatures and were evaluated by using several models (zero order, pseudo-first order, first order, Higuchi, Hixon Crowell, Weibul distribution and Korsmeyer-Peppas). It was found that the best fitting model of the drug release was the Higuchi model. So as to predict character of the release process (exothermic and spontaneous), the activation energy, activation enthalpy, entropy and Gibbs free energy were evaluated.

The paper deals with the kinetics of liberation of chlorhexidine dihydrochloride (CHH) from chitosan-based hydrogels in the presence of the substance with antiseptic effect, namely benzethonium chloride at the temperature range 25 – 40 °C. The concentration of the CHH in the system was 0.1 % (w/w). The used benzethonium chloride was in concentration range of 0.1 – 1.0 % (w/w). It was found that the release of CHH is influenced by both factors: the concentration of benzethonium chloride and temperature. The release rate constants increase with increasing temperature and decrease with increasing concentration of benzethonium chloride in hydrogels. The activation energy of the release of the substance CHH from hydrogel is higher for hydrogels with higher content of benzethonium chloride. The activation energies of the benzethonium chloride release from the prepared hydrogels were virtually the same.