Improving the Solubility, Dissolution, and Bioavailability of Metronidazole via Cocrystallization with Ethyl Gallate

Metronidazole Cocrystal Polymorphs with Gallic and Gentisic Acid Accessed through Slurry, Atomization Techniques, and Thermal Methods

In this study, key features of metronidazole (MNZ) cocrystal polymorphs with gallic acid (GAL) and gentisic acid (GNT) were elucidated. Solvent-mediated phase transformation experiments in 30 solvents with varying properties were employed to control the polymorphic behavior of the MNZ cocrystal with GAL. Solvents with relative polarity (RP) values above 0.35 led to cocrystal I°, the thermodynamically stable form. Conversely, solvents with RP values below 0.35 produced cocrystal II, which was found to be only 0.3 kJ mol-1 less stable in enthalpy. The feasibility of electrospraying, including solvent properties and process conditions required, and spray drying techniques to control cocrystal polymorphism was also investigated, and these techniques were found to facilitate exclusive formation of the metastable MNZ-GAL cocrystal II. Additionally, the screening approach resulted in a new, high-temperature polymorph I of the MNZ-GNT cocrystal system, which is enantiotropically related to the already known form II°. The intermolecular energy calculations, as well as the 2D similarity between the MNZ-GAL polymorphs and the 3D similarity between MNZ-GNT polymorphs, rationalized the observed transition behaviors. Furthermore, the evaluation of virtual cocrystal screening techniques identified molecular electrostatic potential calculations as a supportive tool for coformer selection.

Development of Composite, Reinforced, Highly Drug-Loaded Pharmaceutical Printlets Manufactured by Selective Laser Sintering-In Search of Relevant Excipients for Pharmaceutical 3D Printing

3D printing by selective laser sintering (SLS) of high-dose drug delivery systems using pure brittle crystalline active pharmaceutical ingredients (API) is possible but impractical. Currently used pharmaceutical grade excipients, including polymers, are primarily designed for powder compression, ensuring good mechanical properties. Using these excipients for SLS usually leads to poor mechanical properties of printed tablets (printlets). Composite printlets consisting of sintered carbon-stained polyamide (PA12) and metronidazole (Met) were manufactured by SLS to overcome the issue. The printlets were characterized using DSC and IR spectroscopy together with an assessment of mechanical properties. Functional properties of the printlets, i.e., drug release in USP3 and USP4 apparatus together with flotation assessment, were evaluated. The printlets contained 80 to 90% of Met (therapeutic dose ca. 600 mg), had hardness above 40 N (comparable with compressed tablets) and were of good quality with internal porous structure, which assured flotation. The thermal stability of the composite material and the identity of its constituents were confirmed. Elastic PA12 mesh maintained the shape and structure of the printlets during drug dissolution and flotation. Laser speed and the addition of an osmotic agent in low content influenced drug release virtually not changing composition of the printlet; time to release 80% of Met varied from 0.5 to 5 h. Composite printlets consisting of elastic insoluble PA12 mesh filled with high content of crystalline Met were manufactured by 3D SLS printing. Dissolution modification by the addition of an osmotic agent was demonstrated. The study shows the need to define the requirements for excipients dedicated to 3D printing and to search for appropriate materials for this purpose.