Impregnation of porous supports with active substances by means of supercritical fluids

Publisher Summary In the pharmaceutical industry, the impregnation of porous and inert solids with drugs is classically achieved by a two-step process. During the first step, a solution of the active molecule in an organic solvent is brought into contact with the solid. The second phase deals with the evaporation of the excess solvent. The elimination of the solvent can cause the degradation of thermosensitive drugs. The residual traces of solvent resulting from an incomplete elimination may cause a risk of toxicity. To overcome these problems, it has been suggested to achieve the impregnation using a micronized dispersion of the drug in water. The impregnation of porous supports by drugs can be achieved by means of supercritical fluids. This one-step method yields a final product exempt from any residual trace of toxic solvent. The kinetics of the mass transfer is faster and in addition the thermodynamics of the adsorption seems more favorable. The main problem encountered is the weak solubility of many active molecules in pure CO 2 , which induces a limitation of the percentage of deposited product. However, this difficulty can be overcome by the use of few amount of an entrainer.