Improving the therapeutic efficacy of prilocaine by PLGA microparticles: Preparation, characterization and in vivo evaluation.

A delivery system based on poly(lactic-co-glycolic acid) polymer (PLGA) microparticles has been developed for parenteral administration of the local anesthetic prilocaine in its free base form. Both drug-free and drug-loaded microparticles, prepared by a double-emulsion-evaporation method, were characterized for mean size by Laser Diffraction Analysis, while their morphology was investigated by scanning electron microscopy. The preparation technique allowed obtainment of homogeneous microparticles of about 25 µm diameter, suitable for subcutaneous administration. The encapsulation efficiency, determined by both direct and indirect methods, was around 36-38%. Differential Scanning Calorimetry was used to characterize the solid state of the raw materials, assess drug-polymer compatibility and miscibility and highlight possible modifications of the components induced by the preparation method. In vitro release studies showed a sustained release profile, with about 80% of drug released after the first 24 h. The anesthetic effect of the formulation was evaluated in vivo on rats, according to the test of cutaneous trunci muscle reflex. Administration of prilocaine base as PLGA microparticles allowed to significantly enhance both extent (60% AUC increase) and duration (100% increase) of the anesthetic effect in the animal model, in comparison with the equivalent dose of prilocaine hydrochloride aqueous solution