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Microemulsions based on polyglycerol polyricinoleate as drug delivery systems

The aim of the work is to develop composition of reverse microemulsion stabilized by the surfactant from a number of polyglycerol polyricinoleates for encapsulating water-soluble biologically active substance (BAS) and studying the kinetics of its release into the medium simulating the medium of the small intestine. Materials and methods. Possible stable (equilibrium) phases of the reverse microemulsion in the pseudoternary system water–PG-3-PR/Tween 80–paraffin oil were determined by titration of surfactant/co-surfactant mixtures–oil in water with hydrophilic-lipophilic balance (HLB) values of the surfactant mixture ranging from 4.0 to 7.0. Stability of a number of compositions during storage at 20 °C for 6 months was studied. Based on the obtained data, a composition was selected for encapsulating methylene blue (MS) dye as a model of a water-soluble biologically active substance. Microemulsion was obtained by mixing paraffin oil and surfactants with selected mass ratio followed by the addition of an aqueous phase. Reverse microemulsion morphology was evaluated with transmission electron microscopy (TEM). To evaluate the in vitro drug release rate, aliquots of an aqueous dye solution (control sample) and MB-containing microemulsions were placed in dialysis bags and immersed in 0.01 M phosphate-buffered saline (PBS) (pH 7.4) in a thermostatic shaking incubator at 180 rpm and 37 °C. Aliquots of the release medium were selected at predetermined time intervals and the concentration of MB dye was determined using a UV spectrophotometer at 660 nm. Results. Composition containing 13.5 wt% paraffin oil, 76.5 wt% mixture of PG3-PR/Tween 80 (HLB 5.5) and 10 wt% water was chosen to encapsulate the biologically active agents. Number average droplet diameter in the dispersed phase of the obtained microemulsion was 55 nm. Dye-loaded microemulsion sample showed a prolonged release of biologically active substances within 48 hours of the experiment (15.2%) and low initial release rate. Conclusion. Possible stable phases of reverse microemulsion in the pseudoternary system water–PG-3-PR/Twin 80–paraffin oil were determined in the course of the work and optimal microemulsion composition for encapsulating medicinal substances was found. It was shown that the resulting microemulsion system provides a sustained release of methylene blue as a model of a water-soluble biologically active substance in a medium simulating medium of the small intestine. The obtained data allow to consider this composition as a potential nanoscale system for the sustained delivery of water-soluble drugs.