Continuous Preparation of 1:1 Haloperidol–Maleic Acid Salt by a Novel Solvent-Free Method Using a Twin Screw Melt Extruder

Abstract

Salts are generally prepared by acid-base reaction in relatively large volumes of organic solvents, followed by crystallization. In this study, the potential for preparing a pharmaceutical salt between haloperidol and maleic acid by a novel solvent-free method using a twin-screw melt extruder was investigated. The pH-solubility relationship between haloperidol and maleic acid in aqueous medium was first determined, which demonstrated that 1:1 salt formation between them was feasible (pH 4.8; salt solubility 4.7 mg/mL). Extrusion of a 1:1 mixture of haloperidol and maleic acid at the extruder barrel temperature of 60 °C resulted in the formation of a highly crystalline salt. The effects of operating temperature and screw configuration on salt formation were also investigated, and those two were identified as key processing parameters. Salts were also prepared by solution crystallization from ethyl acetate, liquid-assisted grinding, and heat-assisted grinding and compared with those obtained by melt extrusion by using DSC, PXRD, TGA, and optical microscopy. While similar salts were obtained by all methods, both melt extrusion and solution crystallization yielded highly crystalline materials with identical enthalpies of melting. During the pH-solubility study, a salt hydrate form was also identified, which, upon heating, converted to anhydrate similar to that obtained by other methods. There were previous reports of the formation of cocrystals, but not salts, by melt extrusion. H NMR and single-crystal X-ray diffraction confirmed that a salt was indeed formed in the present study. The haloperidol-maleic acid salt obtained was nonhygroscopic in the moisture sorption study and converted to the hydrate form only upon mixing with water. Thus, we are reporting for the first time a relatively simple and solvent-free twin-screw melt extrusion method for the preparation of a pharmaceutical salt that provides material comparable to that obtained by solution crystallization and is amenable to continuous manufacturing and easy scale up.

Fabrication and Characterizations of Hot-Melt Extruded Nanocomposites Based on Zinc Sulfate Monohydrate and Soluplus

“…A twin screw extruder, compared to single screw extruder, provides the following advantages: a higher dispersibility, easier feeding, a lower risk of overheating, higher process productivity, and a better modulation of process parameters [9,19,20].…”

Melt extrusion with poorly soluble drugs – An integrated review

“…However, the preparation of salts at the industrial scale is a complex high-temperature process, which utilizes large amounts of organic solvents (Wermuth and Stahl, 2002) and thus raises serious environmental concerns. The recent advances in reactive extrusion can be exemplified by the synthesis of a salt of haloperidol and maleic acid via HME (Lee et al, 2017). A highly crystalline salt was obtained by extruding a physical mixture of haloperidol and maleic acid (1:1) at 60 °C.…”

State of the Art of Pharmaceutical Solid Forms: from Crystal Property Issues to Nanocrystals Formulation

“…The compound is then in the crystallines tate, whichi st he ordered form of matter, whereas in the amorphous state, there is no explicit range order.V arious crystalline structures can be used in the pharmaceuticalsciencest oi mprovedrug properties. [12] Polymorphism, first introduced by McCrone in 1965, [13] then by Lamy and Rosenstein in 1969, [14] is the ability of ag iven compound to exist in several crystalline solid states. [15,16] Therefore, polymorphs contain molecules of as ingle chemical nature.T he term packing polymorphism is used when differences in crystal packing are observed:m olecules are in the same molecular arrangement, but are grouped differently in three-dimensional space.…”