On the Dimorphism and the Pressure-Temperature State Diagram of Racemic m-Nisoldipine, a Dihydropyridine Calcium Ion Antagonist

The pressure-temperature phase diagram of the dimorphism of racemic m-nisoldipine is constructed using temperatures and enthalpies of fusion of forms A and B. At ordinary pressure, the transition from form B to form A is found to occur around 192 K, which indicates that these polymorphs are enantiotropically related and that form A is stable at room temperature. Nevertheless, the phase relationship turns to be monotropic when pressures become greater than about 100 MPa, which indicates that form B becomes the sole stable phase.