Alteration of the Solid State of the Drug Substance: Polymorphs, Solvates, and Amorphous Forms

The maximum solubility of a drug substance is a function of the nature of the solid phase in equilibrium with a specified solvent system at a given tem perature and pres­ sure. Solubility is an equilibrium constant for the dissolution of the solid into the sol­ vent and thus depends on the com petition of solute:solvent interactions and solidrsolid interactions. Alteration of the solid phase of the drug substance can influ­ ence its solubility and dissolution properties by affecting the molecular interactions in the solid.