As a BCS II drug, the atypical antipsychotic agent lurasidone hydrochloride (LH) has low oral bioavailability mainly because of its poor aqueous solubility/dissolution. Unexpectedly, amorphous LH exhibited a much lower dissolution than that of its stable crystalline form arising from its gelation during the dissolution process. In the current study, a supramolecular coamorphous system of LH with l-cysteine hydrochloride (CYS) was prepared and characterized by powder X-ray diffraction and differential scanning calorimetry. Surprisingly, in comparison to crystalline and amorphous LH, such a coamorphous system dramatically enhanced solubility (at least ∼50-fold in the physiological pH range) and dissolution (∼1200-fold) of LH, and exhibited superior physical stability under long-term storage condition. More importantly, the coamorphous system was able to eliminate gelation of amorphous LH during dissolution. In order to further explore the mechanism of such improvement, the internal interactions of the coamorphous system in the solid state and in aqueous solution were investigated. Fourier transform infrared spectroscopy, Raman spectroscopy, and solid-state 13C NMR suggested that intermolecular hydrogen bonds formed between the nitrogen atom in the benzisothiazole ring of LH and the NH3+ group of CYS after coamorphization. A fluorescence quenching test with a Stern-Volmer plot and density functional theory modeling, phase-solubility study, and NMR test in D2O indicated that ground-state complexation occurred between LH and CYS in aqueous solution, which contributed to the solubility and dissolution enhancement of LH. The current study offers a promising strategy to overcome poor solubility/dissolution and be able to eliminate gelation of amorphous materials by coamorphization and complexation.
Keywords: coamorphous; complexation; dissolution; gelation; lurasidone hydrochloride; stability.