The objective of this research is to outline the liberation of indomethacin from different chitosan gels containing O/W microemulsion. The influence of surfactant, sodium lauryl sulfate, in two concentrations (0.5% and 0.75%, w/w) was determined in dissolution medium on the release of indomethacin, which was used as poor water-soluble model drug. Chitosan gels were prepared in four different concentrations of chitosan-1%, 1.5%, 2%, and 3% (w/w). Microemulsion enhanced the liberation of the indomethacin from chitosan gels into all dissolution mediums. Adding the surfactant into phosphate-buffered saline decreased the amount of liberated indomethacin from microemulsion, gel mixture, but increased the drug liberation from pure chitosan gels. It was detected that with the increased concentration of chitosan in the samples, the amount of indomethacin liberated (p < 0.05) also increased. A conclusion was drawn that the liberation of indomethacin from chitosan gels was influenced by increased pH of the samples. The high viscosity induced a higher release of indomethacin from 3% (w/w) chitosan hydrogel at pH 5.8 as compared with 3% (w/w) chitosan hydrogel at pH 3.8. The highest percentage of released indomethacin was determined when a mixture of microemulsion gel with higher chitosan content was used.

The paper is focused on liberation of indomethacin from gels and the influence of microemulsion´s presence in the system. Liberation of drug was performed in vitro through a semipermeable membrane and drug quantity was determined spectrophotometrically. Our results pointed out that the influence of microemulsion system on drug liberation depends on the gel selection. The presence of o/w microemulsion in the lipophilic gel (aerosil in liquid paraffin) increased the released amount of the drug approximately 50%. The liberation profile of indomethacin is better when the hydrophilic gel (carbopol) was used. Drug was released in higher amounts from hydrophilic gel comparised to the commercial gel. The presence of microemulsion in carbopol gel did not have any significant influence.

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