Solid Dispersions An Advancement in Solubility Improvement; Strategy, Mechanism and Characterization

Solubility is the phenomenon of dissolution of solid in liquid phase to give a homogenous system. Solubility is one of the important parameter to achieve desired concentration of drug in systemic circulation for pharmacological response to be shown. Poorly water soluble drugs often require high doses in order to reach therapeutic plasma concentrations after oral administration. Low aqueous solubility is the major problem encountered with formulation development of new chemical entities. Any drug to be absorbed must be present in the form of an aqueous solution at the site of absorption. The ability to increase aqueous solubility can thus be a valuable aid to increasing efficiency and/or reducing side effects for certain drugs. This is true for parenterally, topically and orally administered solutions. The solubility of drugs is defined according to (bio-pharmaceutical classification system) BCS classification system which divides drugs to different class according to its solubility. Solid dispersion is defined as dispersion of one or more active ingredients in an inert carrier or matrix known as solid dispersion. Solid dispersion reduces the particle size and changes the micro environment of the drug particle, increases the rate of dissolution and absorption and thus changes the biopharmaceutical properties of poorly water soluble drugs. The solid dispersion method, by which a drug is dispersed in a carrier to make it amorphous, is one of the pharmaceutical approaches most commonly employed to enhance bioavailability of poorly water soluble drugs. Various pharmaceutical approaches for the preparation of SDs, including co-precipitation, lyophilization, spray drying, solvent evaporation, fusion and powder mixing methods, have been reported. It’s a new and efficient technique to improve the solubility of poorly soluble drugs.