Pharmaceutical formulations, like other formulations, are mixtures, almost by definition. Once the excipients have been selected in the quite early stages of a product's development, probably subsequent to excipient compatibility studies of the kind described in chapter 2, the effects of different proportions of the excipients on characteristics of the formulation would normally be investigated. These characteristics include both the (final) properties of the dosage form and the ease
of processing. They are defined in terms not of the amounts of the different constituents, but of their relative proportions.