Study of Favipiravir Micronization by Rapid Expansion of a Supercritical Solution

Rapid expansion of supercritical solutions for the preparation of nano- and microparticles is studied. The theoretical analysis of this process considers the mechanism of particle formation involving solution supersaturation, nucleation, condensation, and coagulation. The size of the obtained particles is shown to be influenced by the starting concentration of the micronized substance and the structural features of the device, in addition to pressure and temperature. The experimental section describes a laboratory device for rapid expansion of supercritical solutions. Experiments on micronization of favipiravir are carried out at different temperatures and pressures. The average size of the starting particles is 12.5 µm; micronization afforded particles with a size in the range from 0.45 to 1.07 µm, depending on the temperature and pressure. Simultaneous increase in the temperature and pressure is found to result in a decrease in the particle size. X-ray powder diffraction analysis shows the obtained favipiravir particles to have an amorphous structure.