Fabrication, characterization, and controlled release of eprinomectin from injectable mesoporous PLGA microspheres

Batches of mesoporous poly(lactide-co-glycolide) (PLGA) microspheres were fabricated via an O/W emulsion–solvent evaporation method. The obtained microspheres were detected with scanning electron microscopy (SEM, S-4800) to observe their surface morphology. On observation it was found that many macropores were distributed on the microsphere surfaces. Then, eprinomectin (EPR) was employed as a model drug and was encapsulated by these mesoporous microspheres. The distribution state of the EPR in the microspheres was investigated via X-ray diffraction and differential scanning calorimetry. The test results indicated that the EPR was distributed in the microspheres with an amorphous state. After re-dispersing the EPR-loaded microspheres in ultrapure water, an extended-release formulation of EPR was obtained. The formulation was administered to Japanese white rabbits by subcutaneous injection to monitor the blood concentration of EPR. Plasma concentration profiles showed that the Cmax of EPR (38.80 ± 9.50 ng mL−1) appeared on the 2nd day after subcutaneous injection. During the next 40 days, the plasma concentration of EPR maintained a value of 30.0 ng mL−1. In addition, the biocompatibility of the EPR-loaded mesoporous microspheres (EPM) was also investigated by a biological sectioning method. Photographs of the histological sections illustrated that the EPM did not trigger a serious stimulus response at the injection site. Thus, they could be used to affirm that the mesoporous microspheres have a promising application in controlling veterinary drugs for sustained release.