Fundamentals of Amorphous Systems: Thermodynamic Aspects

Abstract

Drugs that are poorly soluble in water present a major challenge to the pharmaceutical industry because they tend to show poor oral bioavailability. To overcome this problem, much attention has been given to delivering drugs in formulations that supersaturate in the gastrointestinal (GI) fluids. One approach to achieve the supersaturation is to formulate drugs in amorphous forms. This chapter considers amorphous forms of the pure active pharmaceutical ingredients (APIs), also known as neat amorphous APIs. The relationship between supersaturation and absorption is discussed, along with the thermodynamics of solubility of supersaturated solutions. The relevant properties of neat amorphous APIs are discussed and explained in terms of thermodynamics and microscopic models, and their relationships to improved solubility/dissolution and physical stability are considered. In addition, the relationship between neat amorphous forms and glasses, especially as presented in the literature, is reviewed.