Polymorph transitions of bicalutamide: a remarkable example of mechanical activation

Bicalutamide, an active pharmaceutical ingredient possessing antiandrogenic activity, is known to exhibit polymorphism. The higher melting Form I relates monotropically to the lower melting Form II. The amorphous form can be easily produced by quench cooling the melt, but it is known to crystallize spontaneously to Form II at room temperature within days. Our results show that crystallization of amorphous bicalutamide is greatly influenced by experimental conditions and sample treatment. The effect of mechanical activation on the polymorph transitions is investigated in detail. Seeds of Form I can be formed in the amorphous phase even due to gentle mechanical treatment, which results in crystallization to the more stable structure at elevated temperature. The crystalline Form II may as well be transformed to the stable modification through mechanical activation at elevated temperature.