Solid Dispersion – a Promising Novel Approach for Improving the Solubility of Poorly Soluble Drugs

Solid dispersions is an efficient means of improving the dissolution rate and hence the bioavailability of a range of poorly soluble drugs. This article reviews the various types of solid dispersion, preparation techniques for solid dispersion and compiles some of the recent technologies. Some of the practical aspects to be considered for the preparation of solid dispersions, such as selection of carrier and methods of physicochemical characterization, along with nature of drugs in solid dispersions are also discussed. Finally, limited commercialization of solid dispersions and recent revival has been considered. INTRODUCTION: Therapeutic effectiveness of a drug depends upon the bioavailability and ultimately upon the solubility of drug molecules. Solubility behavior of a drug is one of the key determinants of its oral bioavailability. In recent years, the number of poorly soluble drug candidates has increased tremendously. The formulation of poorly soluble drugs for oral delivery presents a challenge to the formulation scientists. The rate and extent of dissolution of the active ingredient from any dosage form often determines the rate of extent of absorption of the drug. When an active agent given orally, it must first dissolve in gastric and/or intestinal fluids before it can then permeate the membranes of the GI tract to reach systemic circulation. Therefore, a drug with poor aqueous solubility will typically exhibit dissolution rate limited absorption, and a drug with poor membrane permeability will typically exhibit permeation rate limited absorption. Hence, two areas focus on improving the oral bioavailability of active agents include: (i) enhancing solubility and dissolution rate of poorly water-soluble drugs and (ii) enhancing permeability of poorly permeable drugs. This article focuses on the former, in particular, the use of solid dispersion technologies to improve the dissolution characteristics of poorly water-soluble drugs and in turn their oral bioavailability. In case of poorly water soluble drugs, dissolution may be the rate-limiting step in the process of drug absorption. Drug with poor water solubility have been shown to be unpredictably and slowly absorbed compared with drugs of higher solubility. Therefore, a better oral, parenteral, or topical formulation can be developed by increasing the water solubility of the drugs. There are various techniques available to improve the solubility of poorly soluble drugs, such micronization, nanosuspension, modification of the crystal habits, eutectic mixtures, solid dispersions, micro emulsions, self micro emulsifying drug delivery systems, cyclodextrin inclusion and lipid based delivery systems etc. This review focuses on the solid dispersion