Phenomenology of polymorphism: The topological pressure–temperature phase relationships of the dimorphism of finasteride

Knowledge of the phase behavior in the solid state of active pharmaceutical ingredients is important for the development of stable drug formulations. The topological method for the construction of pressure–temperature phase diagrams has been applied to study the phase behavior of finasteride. It is demonstrated that with basic calorimetric measurements and X-ray diffraction sufficient data can be obtained to construct a complete topological pressure–temperature phase diagram. The dimorphism observed for finasteride gives rise to a phase diagram similar to the paradigmatic diagram of sulfur. The solid–solid phase relationship is enantiotropic at ordinary pressure and becomes monotropic at elevated pressure, where solid I is the only stable phase.

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► The topological pressure–temperature phase diagram for the dimorphism of finasteride.
► Pressure affects phase equilibria: an enantiotropic phase relationship turning monotropic at high pressure.
► The influence of pressure on phase behavior inferred from data obtained under ordinary conditions.