Physical Pharmacy

In this chapter, we focus on solutions. In the introduction, general and descriptive aspects are defined, such as the classification of solutions and the addition of solids. Considering the properties of these systems, we focus on definitions related to colligative properties, and on the use of this property for the adjustment of isotonic solutions considering the selective capacity of the membranes, differentiation of tonicity and osmolarity. We also introduce the calculations necessary for the preparation of isotonic solutions with blood plasma, using the mass and volume adjustment method. The solutions require different methods of expressing their concentration, and in order to develop this point, we present the different forms of expression, with extensive detail on one of the variables, i.e., normality, very important in the formulation of parenteral solutions. Since the preparation of solutions is an important aspect, we detail the existing interactions between the solute and the solvent, specify the thermodynamic aspects that condition the solubility of the solute in the solvent, and develop variables such as polar interactions, capacities to accept or give Hydrogen bridge junctions and the energy requirement to generate space within the solvent, giving a rational look at the process of improving the capacity of the solvent to contain the solute. The dissolution rate is another variable developed through simple equations, which make an analysis of the factors that modify it, such as agitation, temperature, particle size, and diffusion coefficient. We also describe variables such as the pH and the dielectric constant of the solvent to modify solubility.