Solubility Enhancement of Poorly Water Soluble Drugs by Solid Dispersion

Solid dispersions have been employed to enhance the dissolution rates of poorly water-soluble drugs. Many approaches have been investigated for the preparation of solid dispersions. This paper reports the various solubility enhancement strategies in solid dispersion. The approaches described are fusion (melting), solvent evaporation, lyophilization (freeze drying), melt agglomeration process, extruding method, spray drying technology, use of surfactant, electro static spinning method and super critical fluid technology. This paper also highlights the potential applications and limitations of these approaches in solid dispersions. INTRODUCTION: Drug substances are seldom administered alone, but rather as part of a formulation in combination with one or more non-medicinal agents that serve varied and specialized pharmaceutical function. The proper design and formulation of a dosage form requires consideration of the physical, chemical and biological characteristics of all the drug substances and pharmaceutical ingredients to be used in fabricating the product. An important physical-chemical property of a drug substance is solubility, especially aqueous system solubility. A drug must posses some aqueous solubility for therapeutic efficacy. For a drug to enter the systemic circulation to exert a therapeutic effect it must be in solution . Recent technologies innovation of combinatorial chemistry and high throughput screening can effectively discover the seeds of new drugs, which present good pharmacological activities. However 35-40 % of these new drugs discovered by those technologies suffer from poor aqueous solubility . The solubility/dissolution behavior of a drug is key determinant to its oral bioavailability, the latest frequency being the rate-limiting step to absorption of drugs from the gastrointestinal tract . Consequently poor solubility results in low bioavailability, increase in the dosage, large inters and intra-subject variation and large variations in blood drug concentrations under fed versus fasted conditions. Improvement of oral bioavailability of poorly watersoluble drugs remains one of the most challenging aspects of drug development. The techniques/ approaches that have commonly been used to overcome drawbacks associated with poorly watersoluble drugs, in general includes micronization, salt formation, use of surfactant and use of prodrug . However, all these techniques have potential limitations.