Reversibility of enantiotropically related polymorphic transformations from a practical viewpoint: thermal analysis of kinetically reversible/irreversible polymorphic transformations.

Although enantiotropically related polymorphic transitions are thermodynamically reversible with temperature and pressure, they may be observed as either reversible or irreversible in practical investigations. This behavior may be explained simply by a difference in the energy barrier for the transition. However, this difference may have a significant effect on strategy in formulation development. This article summarizes the characteristics of enantiotropic transitions with reference to the literature. Also provided are careful investigations of polymorphic transitions by thermal analysis, which is the most promising method to investigate transition behavior. (c) 2006 Wiley-Liss, Inc. and the American Pharmacists Association.