Fluorescence studies of the transformation of carbamazepine anhydrate form III to its dihydrate phase.

It has been found that both the anhydrous Form III and dihydrate phases of carbamazepine exhibit fluorescence in the solid state. The fluorescence intensity associated with the dihydrate phase was determined to be significantly more intense than that associated with the anhydrate phase, and this difference was exploited to develop a method for study of the kinetics of the aqueous solution-mediated phase transformation between these forms. Studies were conducted at temperatures over the range 18-40 degrees C, and it was found that the phase transformation was adequately characterized by first-order reaction kinetics. The temperature dependence in the calculated rate constants was used to calculate an activation energy of 11.2 kcal/mol (47.4 cal/g) for the anhydrate-to-dihydrate phase conversion. Copyright 2004 Wiley-Liss, Inc. and the American Pharmacists Association