Confirmation of More Stable Polymorphic Form of Etoricoxib at Room Temperature

Abstract

Polymorphic forms of etoricoxib have been reported in the literature, and form I was considered to be the most stable one. However, in this work, it was found that form I and form V are enantiotropic by differential scanning calorimetry analysis, solubility measurements, and solution-mediated polymorphic transformation experiments with form V being more stable than form I at room temperature. Thermodynamic transition temperature is determined as (353.45 ± 0.10) K. Besides, form V would transform to form I with the seeding effect of form I at high temperature below the melting point of form V. The crystal structure of form V was solved for the first time. The molecules in form V are linked by weak hydrogen bond C-H⋯O to form ring motif, which is nonexistent in form I.

Keywords: crystal structure; enantiotropic system; etoricoxib; polymorphism; solubility; stability; transformation.