Strategies to Enhance Solubility and Dissolution of a poorly water soluble drug

Abstract

Solid dispersion is used for enhancing dissolution rate of a therapeutically active substance and in turns its absorption and in vivo efficacy. Solid dispersion is generally prepared with drug which is having poor aqueous solubility and hydrophilic carrier. Generally polyethylene glycol, polyvinyl pyrrolidone, mannitol, urea, gums, eudragit are used as hydrophilic carriers. Certain hydrophilic swellable polymers sodium carboxy methyl cellulose, pregelatinized starch, sodium starch glycolate are also used. Sometimes surfactant is also added to further improve wetting property of solid dispersion. In solid dispersion particle size of drug is reduced or a crystalline pure drug is converted into amorphous form and hence the solubility of drug is increased. Solid dispersion is not only used in improving dissolution rate of poorly water soluble drug but also in masking the taste of the drug substance, preparing rapid disintegration oral tablets and in producing sustained release microspheres. Various methods are available to prepare solid dispersion generally solvent evaporation method, melting method, melt solvent method, kneading method, co-grinding method, co-precipitation method, modified solvent evaporation method, spray drying, gel entrapment technique, co-precipitation with supercritical fluid. Evaluations of solid dispersion are done by Fourier Transform infra- red spectroscopy, X-Ray diffractometry, scanning electron microscopy, differential scanning calorimetry, solubility and dissolution experiments.