Anhydrous mirtazapine crystals and process for preparing the same

Abstract

Low-hygroscopic anhydrous mirtazapine crystals having a hygroscopic degree of not more than 0.6% by weight when the crystals are stored in the air having a relative humidity of 75% at 25° C. under atmospheric pressure for 500 hours; a process for preparing anhydrous mirtazapine crystals having a hygroscopic degree of not more than 0.6% by weight when the crystals are stored in the air having a relative humidity of 75% at 25° C. under atmospheric pressure for 500 hours, comprising drying crystals of mirtazapine hydrate; a crystal of a mirtazapine hydrate represented by the formula (I): wherein n is an integer of 1 to 5; and a process for preparing crystals of a mirtazapine hydrate, comprising crystallizing a crude mirtazapine using a water-soluble organic solvent and water. The anhydrous mirtazapine crystals can be suitably used, for instance, as an antidepressant.

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