ABSTRACT
The primary interest for pharmaceutical formulators is delivery of the active molecule to the target tissue at therapeutically relevant concentrations accompanied by negligible side effects. Drug delivery is often signi cantly in uenced by the physicochemical properties of the active compound, particularly its solubility. The water solubility of drug molecules and gastrointestinal (GI) permeability are the basic criteria for the biopharmaceutical classi cation system of drugs comprising four classes (I-IV; Amidon et al., 1995). Class II and class IV cover drugs with low water solubility and high and low GI permeability, respectively. The primary limitation to the absorption of class II drugs is the slow dissolution rate in GI uids, but poor absorption in class IV drugs is attributed to hindered permeability. Additionally, roughly 40% of the newly discovered chemical entities entering drug development programs are poorly water-soluble compounds. Thus, the solubility issue affects the bioavailability and ef cacy of many existing and potential drugs. Various conventional formulation strategies for the improvement of the solubility and dissolution kinetics of drugs that have been developed (e.g., particle size reduction, synthesis of salts freely soluble in water, pH adjustment, addition of solubilizing agents) cannot provide satisfactory bioavailability enhancement in some cases. Therefore, researchers have made great efforts to develop new approaches for the successful delivery of poorly soluble drugs that will also be economically acceptable for the pharmaceutical industry. An important aspect of any new strategy for delivery of such drugs is to increase their solubility in biological milieu. Novel prospects to overcome problems regarding the limited
10.1 Introduction ..........................................................................................................................245 10.2 Self-Microemulsifying Drug Delivery Systems ................................................................... 247
10.2.1 Self-Microemulsifying Drug Delivery Systems in Oral Delivery of Poorly Soluble Drugs ................................................................................................ 247
10.2.2 Self-Microemulsifying Drug Delivery Systems for Parenteral Administration .......256 10.2.3 Self-Microemulsifying Drug Delivery Systems for Topical Delivery ...................... 257
10.3 Microemulsions as Media for Synthesis of Nanoparticles ................................................... 258 10.3.1 Solid Lipid Nanoparticles Produced by Microemulsion Technique ......................... 258 10.3.2 Microemulsions as Media for Synthesis of Polymeric Nanoparticles ......................260 10.3.3 Microemulsions in Nanoengineering of Poorly Soluble Drugs ................................ 261
10.4 Recent Developments and Future Directions ....................................................................... 262 Abbreviations .................................................................................................................................265 References ......................................................................................................................................265
