Solid-state study of polymorphic drugs: carbamazepine

Polymorphs of a compound have solid crystalline phases with different internal crystal lattices; in pharmaceuticals,differences due to polymorphism and pseudopolymorphism can affect bioavailability and effective clinical use. Theaim of this work was to obtain the different polymorphic modifications of the anticonvulsant drug, carbamazepine,and to characterise them by means of typical structure-sensitive analytical techniques, such as FT-IR spectroscopy,XRPD and DSC. Further investigations were also performed by Hot Stage FT-IR thermomicroscopy, whichpermitted the visible and spectroscopic characterisation of the polymorphic forms during heating. Our results confirmthe existence of three different polymorphic forms for anhydrous carbamazepine: Form III, the commercial one,Form I, obtained by heating Form III and Form II, crystallised from ethanolic solution. Substantial differences weredetected among the polymorphs with regard to solid-state properties. Moreover, Hot Stage FT-IR thermomicroscopyproved its analytical potential to characterise the drug’s polymorphism.