An example of application of a mixture design with constraints to a pharmaceutical formulation

The aim of this tutorial is to show the application of a mixture experimental design to a problem of pharmaceutical formulation. A gel, based on poloxamer 407, useful for topical administration of tolfenamic acid, a potent anti-inflammatory drug very poorly soluble in water, has been prepared, and a mixture experimental design was used to study the influence of the components on the viscosity of the formulation. Its application allowed to identify a critical boundary, separating semisolid formulations from liquid ones, within a narrow interval of concentrations of the components, and to estimate their effects on the viscosity of the preparation.