Effect of polyethylene glycol additives on the polymorph and crystal habit of carbamazepine

• Carbamazepine crystallization with different molecular weight polyethylene glycol was studied. • An effective method for stabilizing metastable crystal form was proposed. • Increasing the molecular weight of the polyethylene glycol additive decreased the aspect ratio of crystal. The effect of polyethylene glycol (PEG) with different molecular weights on carbamazepine (CBZ) crystallization was investigated by experiments and molecular dynamics (MD) simulations. The influence of PEG on the crystal morphology and solvent-mediated phase transition of CBZ was studied. It was found that PEG inhibited the CBZ III nucleation and CBZ II transition. The crystal morphology changes significantly from needle to rod when adding PEG with a molecular weight greater than 1500. MD simulations show that the binding energy sequence between the additive and the crystal surface is: E b (1 –1 –1) > E b (2 –2 1) > E b (2 –1 0), which explains the suppression of axial crystal growth. The results provide a possible method to stabilize the metastable crystal form of CBZ and improve crystal morphology.