The kinetic dissolution behaviour of carbamazepine (CBZ) polymorphs, three anhydrous forms (I, II, and III forms) and one dihydrate form (IV form), were investigated in detail by the rotating disk and dispersion methods. All of anhydrous forms showed a simultaneous phase transition from an anhydrous form to a dihydrate form during dissolution. Accordingly, a model involving a term of phase transition during dissolution was used, and the solubilities of anhydrous forms, C
aa, and the rate constants of crystallization process, k
r, were calculated by the rotating disk method. I and II forms showed the highest values of the solubility and the phase transition rate, respectively. Furthermore, the values of C
aa and k
r obtained by the dispersion method used in the above model adding a term of variable particle size were in fair agreement with those by the rotating disk method.
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