Thermal properties of binary mixtures of β-cyclodextrin with carbamazepine polymorphs

The thermal behaviour of binary mixtures between beta-cyclodextrin (beta-CD) and either carbamazepine polymorphic Form I (CBZ I), Form III (CBZ III) or dihydrate was investigated in order to assess possible interactions of CBZ solid phases with beta-CD. Physical mixtures and kneaded binaries of beta-CD and different CBZ crystal forms were studied by differential scanning calorimetry, thermogravimetric analysis and hot stage microscopy. The pattern of transition of CBZ Form III into Form I is strongly influenced by beta-CD. The liquid-solid transition is practically absent when anhydrous CBZ/beta-CD mixes are tested, as a consequence of an interaction between beta-CD and liquid CBZ that hinders CBZ recrystallisation as Form I occurring after CBZ Form III melting. Water loss on heating of CBZ dihydrate in the presence of beta-CD leads in all cases to the formation of CBZ Form I.