On the Thermal Stability of the Diethylcarbamazine-Fortified Table Salt Used in the Control of Lymphatic Filariasis

The use of variable temperature 13 C solid-state MAS NMR and GIPAW DFT calculations to explore the dynamics of diethylcarbamazine citrate

Experimental ¹³ C solid-state magic-angle spinning (MAS) Nuclear Magnetic Resonance (NMR) as well as Density-Functional Theory (DFT) gauge-including projector augmented wave (GIPAW) calculations were used to probe disorder and local mobility in diethylcarbamazine citrate, (DEC)⁺ (citrate)^- . This compound has been used as the first option drug for the treatment of filariasis, a disease endemic in tropical countries and caused by adult worms of Wuchereria bancrofti, which is transmitted by mosquitoes. We firstly present 2D ¹³ C─¹ H dipolar-coupling-mediated heteronuclear correlation spectra recorded at moderate spinning frequency, to explore the intermolecular interaction between DEC and citrate molecules. Secondly, we investigate the dynamic behavior of (DEC)⁺ (citrate)^- by varying the temperature and correlating the experimental MAS NMR results with DFT GIPAW calculations that consider two (DEC)⁺ conformers (in a 70:30 ratio) for crystal structures determined at 293 and 235 K. Solid-state NMR provides insights on slow exchange dynamics revealing conformational changes involving particularly the DEC ethyl groups.

Protective Layer Development for Enhancing Stability and Drug-Delivery Capabilities of DES Surface-Crystallized Coatings

Carrier-free drug-eluting stents (DES)-based crystalline coatings are gaining prominence because of their function, skipping many limitations and clinical complications of the currently marketed DES. However, their usage has been humbled by inflexibility of the crystalline coating and limited mechanical and physical properties. This study reports for the first time the development of a protective top coating for enhancing the merits and delivery capabilities of the crystalline coating. Flexible and water-soluble polysaccharide top coating was developed and applied onto rapamycin (RM) crystalline carpet. The top coating prevented crystalline coating delamination during stent crimping and expansion without affecting its release profile. Crystalline coating strata and its interfaces with the metallic substrate and top coating were fully studied and characterized. The crystalline top-coated stents showed significant physical, mechanical, and chemical stability enhancement with ∼2% RM degradation after 1 year under different storage conditions. Biocompatibility study of the top-coated stents implanted subcutaneously for 1 month into SD rats did not provoke any safety concerns. Incorporating RM into the top coating to develop a bioactive protective coating for multilayer release purposes was also investigated. The developed protective coating had wide applicability and may be further implemented for various drugs and implantable medical devices.

Mechanochemically induced solid state transformations: The case of raloxifene hydrochloride

Raloxifene hydrochloride is a benzothiophene derivative mainly used in the prevention and treatment of osteoporosis, but exhibits a low bioavailability hindered by its poor water solubility. In this study, a mechanochemical approach based on neat and liquid-assisted grinding was applied to produce new solid forms of raloxifene hydrochloride. The solids obtained were characterized by several solid-state techniques, such as powder X-ray diffraction, thermal analysis, infrared and Raman spectroscopy. These results showed that depending on the processing conditions solvated or amorphous forms can be produced. The thermal stability of the new forms was also investigated showing that the new forms convert back into the raw material form, as observed by Raman spectroscopy, which was successfully used to discriminate amorphous and crystalline forms, as well as, to monitor in situ the recrystallization process. Furthermore, the solubility of the new forms was evaluated, showing the clear advantage of the amorphous form, when compared with the currently marketed salt.

Probing intermolecular interactions in a diethylcarbamazine citrate salt by fast MAS 1H solid-state NMR spectroscopy and GIPAW calculations

Fast magic-angle spinning (MAS) NMR is used to probe intermolecular interactions in a diethylcarbamazine salt, that is widely used as a treatment against adult worms of Wuchereria bancrofti which cause a common disease in tropical countries named filariasis. Specifically, a dihydrogen citrate salt that has improved thermal stability and solubility as compared to the free form is studied. One-dimensional ¹H, ¹³C and ¹⁵N and two-dimensional ¹H-¹³C and ¹⁴N-¹H heteronuclear correlation NMR experiments under moderate and fast MAS together with GIPAW (CASTEP) calculations enable the assignment of the ¹H, ¹³C and ¹⁴N/¹⁵N resonances. A two-dimensional ¹H-¹H double-quantum (DQ) -single-quantum (SQ) MAS spectrum recorded with BaBa recoupling at 60kHz MAS identifies specific proton-proton proximities associated with citrate-citrate and citrate-diethylcarbamazine intermolecular interactions.