Formation of simvastatin nanoparticles from microemulsion

The present study evaluates a new method to prepare nanoparticles of a poorly water-soluble drug, simvastatin, by evaporation of all solvents from spontaneously formed oil-in-water microemulsions. By this method, microemulsions containing a volatile solvent as an oil phase are converted into nanoparticles in the form of dry non-oily flakes by freeze-drying. The presence of simvastatin in nanoparticles was determined by dispersing the flakes in water and subsequent filtering through a 0.1-mu m filter, followed by measuring the simvastatin concentration in the filtrate. It was found that after freeze-drying more than 95% of the drug was present in amorphous particles, smaller than 100 nm. It was found that tablets containing the flakes of simvastatin nanoparticles showed tremendous enhancement in dissolution profile compared with conventional tablets. X-ray diffraction revealed that in the resulting flakes simvastatin nanoparticles were initially amorphous, but a slow crystallization process took place when the product was stored at room temperature.