Physical Chemistry

Many pharmaceutical dosage forms are liquids or semi-liquids such as solutions, colloidal systems, suspensions and emulsions. This chapter deals with the physico-chemical backgrounds that are important for the preparation of these types of dosage forms. Successively solubility, rheology, phase behavior, interfaces, surface active agents, disperse systems and osmosis are addressed. Physical chemistry plays an important role in the design of liquid or semi-liquid pharmaceutical dosage forms. By changing physico-chemical parameters intentionally or unintentionally, the biopharmaceutical properties and thus the therapeutic activity of an active substance can drastically change. Many physicochemical properties are related to each other. For example, changing the composition of a solvent mixture does not only affect its solubility for an active substance but also its surface tension, osmotic value, etc. The chapter is primarily intended to explain physico-chemical aspects described in other chapters. Many examples of the design of pharmaceutical preparations are described to clarify and illustrate the concepts, considering excipients as well as active substances, and small molecules as well as proteins. Also attention is given to the stabilisation of proteins by freeze drying them together with sugars.