Reverse micelle-based microencapsulation of oxytetracycline hydrochloride into poly-d,l-lactide-co-glycolide microspheres.

The objectives of this study were to solubilize oxytetracycline hydrochloride (HCl) in reverse micelles to prepare poly-d,l-lactide-co-glycolide (PLGA) microspheres and to explore parameters affecting its encapsulation efficiency. Oxytetracycline HCl was dissolved in the reverse micelles consisting of cetyltrimethylammonium bromide, water, and ethyl formate. A PLGA polymer was then dissolved in the reverse micellar solution, and a modified solvent quenching procedure was carried out to prepare PLGA microspheres. Encapsulation efficiencies of oxytetracycline HCl ranged from 2.3 +/- 0.2 to 24.9 +/- 4.6%, depending on experimental conditions. Important parameters affecting its encapsulation efficiency included the amounts of water used to prepare the reverse micelles and PLGA polymer. With regard to microsphere morphology, the reverse micellar process produced the microspheres with smooth and pore-free surfaces. In particular, their internal matrices did not possess hollow cavities that were frequently observed when a typical double emulsion technique was used to make microspheres. In summary, it was possible to encapsulate oxytetracycline HCl into PLGA microspheres via the ethyl formate-based reverse micellar technique. We also anticipate that the use of ethyl formate could avoid environmental and human toxicity issues associated with methylene chloride.