Effect of sulfobutyl ether-β-cyclodextrin and propylene glycol alginate on the solubility of clozapine

Abstract

Clozapine (CLZ) is an atypical antipsychotic medication used in the treatment of schizophrenia and is poorly soluble in water (0.05 mM). In this study, we have investigated the effect of β-cyclodextrin (CD) and its derivatives on the solubility of CLZ. The solubility of the CLZ was measured to generate a phase solubility diagram, and the interaction between CLZ and sulfobutyl ether-β-cyclodextrin (SBE-β-CD) in aqueous solution was observed by ¹H- and 2D rotating-frame Overhauser enhancement spectroscopy (ROESY)-NMR methods. Moreover, the synergistic effect of SBE-β-CD and water-soluble polymers, including polyvinylpyrrolidone, hydroxypropyl methylcellulose, carboxymethylcellulose sodium salt, polyvinyl alcohol, sodium alginate, and propylene glycol alginate (PGA), on the solubility of CLZ was investigated. The results show that the solubility of CLZ with 1 w/v% PGA was 7.6 mM, which was almost four times greater than that of CLZ without PGA in a 15 mM SBE-β-CD solution. In contrast, the solubility of CLZ with 1 w/v % PGA in an aqueous solution decreased by one-third relative to that of CLZ in a 15 mM SBE-β-CD solution. 2D ROESY-NMR indicated that a CLZ/SBE-β-CD/PGA ternary complex formed. It was found that the combination of PGA and SBE-β-CD enhanced the solubility of CLZ.

Keywords:

• Clozapine
• cyclodextrins
• propylene glycol alginate
• solubility
• ternary complex
• NMR spectrum

Acknowledgments

The authors are grateful to Prof. Dr. Kimio Higashiyama and Dr. Mayumi Ikegami-Kawai at Hoshi University for their insightful comments and suggestions for NMR measurements. Mr. Ayato Satomi, Mrs. Mariko Fukumura, and Yuka Ikenami are acknowledged for their assistance in conducting the experiments.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported in part by a grant from the Strategic Research Foundation Grant-aided Project for Private Universities; a matching fund subsidy from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) 2008–2012 (to all authors); and partly by a Grant-in-Aid for Young Scientists (B) 25870795 from MEXT 2013–2014 in Japan and Hoshi University Grant-in-Aid for Leading Research Project 2017 (to T.F.).