Mechanochemical Synthesis and Physicochemical Characterization of Previously Unreported Praziquantel Solvates with 2-Pyrrolidone and Acetic Acid

Mechanochemical Synthesis of New Praziquantel Cocrystals: Solid-State Characterization and Solubility

New cocrystals of praziquantel with suberic, 3-hydroxybenzoic, benzene-1,2,4,5-tetracarboxylic, trimesic, and 5-hydroxyisophthalic acids were obtained through ball milling experiments. The optimal conditions for the milling process were chosen by changing the solvent volume and the mechanical action time. Supramolecular interactions in the new cocrystals are detailed based on single-crystal X-ray diffraction analysis, confirming the expected formation of hydrogen bonds between the praziquantel carbonyl group and the carboxyl (or hydroxyl) moieties of the coformers. Different structural characterization techniques were performed for all samples, but the praziquantel:suberic acid cocrystal includes a wider range of investigations such as thermal analysis, infrared and X-ray photoelectron spectroscopies, and SEM microscopy. The stability for up to five months was established by keeping it under extreme conditions of temperature and humidity. Solubility studies were carried out for all the new forms disclosed herein and compared with the promising cocrystals previously reported with salicylic, 4-aminosalicylic, vanillic, and oxalic acids. HPLC analyses revealed a higher solubility for most of the new cocrystal forms, as compared to pure praziquantel.

Differentiation of solvatomorphs of active pharmaceutical ingredients (API) by solid-state vibrational circular dichroism (VCD)

Here, we present the new application of solid-state Vibrational Circular Dichroism (VCD) spectroscopy to differentiate several dutasteride (DS) solvatomorphs - the model active pharmaceutical ingredient (API). Several crystalline DS hydrochloride hydrates solvated with methanol, ethanol, acetonitrile, acetone, and acetic acid were prepared. In contrast to almost identical IR spectra, the VCD ones were very sensitive to changes in the sample composition. We marked significant differences in the shape of VCD spectra of studied DS solvatomorphs, DS hydrates, and DS polymorphic forms. Our findings, supported by DFT calculations, show that VCD spectroscopy has the pronounced ability to distinguish their crystal arrangements. We believe that this contribution will extend the use of VCD in the pharmaceutical industry for developing and designing new chiral drug products for the identification, description, and in-depth probing of several pharmaceutical solvatomorphs in the future.

Product contamination during mechanochemical synthesis of praziquantel co-crystal, polymeric dispersion and cyclodextrin complex

This paper aims to evaluate the product contamination by elemental impurities during the mechanochemical synthesis of praziquantel (PZQ) co-crystal, polymeric dispersion and cyclodextrin complex by grinding. To assess that, PZQ was co-ground with malic acid (MA), Poloxamer F-127 (F-127) and hydroxypropyl-β-cyclodextrin (HPβCD) in high-energy vibrational mills using stainless steel and agate grinding tools, applying different processing time (30 and 90 min). Differential scanning calorimetry and X-ray powder diffraction confirmed the formation of the targeted products, regardless of applied processing time and grinding tool type. After digestion of the solid powder products, the levels of selected elemental impurities were analysed by inductively coupled plasma mass spectrometry (ICP-MS). The analysis revealed that the content of Mg, Ca, and V are below the limit of quantification in all samples analysed. The contents of P and Na are not related to the type of ball mill and reaction time, but to the starting materials themselves, considering that Na is found in HPβCD and MA, while P was found in F-127. The detected Si impurities in the co-ground products can be related to the use of the agate balls and jars, while the presence of Cr and Fe can be related to the use of the stainless steel grinding tools. The risk assessment showed that the oral administration of the prepared co-ground products in quantities corresponding to regular PZQ oral doses resulted in only insignificant exposure to Cr. Finally, the use of agate grinding tools should be preferred, as administration of such products results in lower Cr exposure. The presented elemental impurities did not lead to any significant drug degradation as PZQ content at the end of the six-month testing period was still in the range of 95-105 % of the initial content. Regardless, ICP-MS analysis of the elemental impurities should be considered in regular quality control procedures in the development and production of novel pharmaceutical products prepared by grinding.

Praziquantel Fifty Years on: A Comprehensive Overview of Its Solid State

This review discusses the entire progress made on the anthelmintic drug praziquantel, focusing on the solid state and, therefore, on anhydrous crystalline polymorphs, amorphous forms, and multicomponent systems (i.e., hydrates, solvates, and cocrystals). Despite having been extensively studied over the last 50 years, new polymorphs and the greater part of their cocrystals have only been identified in the past decade. Progress in crystal engineering science (e.g., the use of mechanochemistry as a solid form screening tool and more strategic structure-based methods), along with the development of analytical techniques, including Synchrotron X-ray analyses, spectroscopy, and microscopy, have furthered the identification of unknown crystal structures of the drug. Also, computational modeling has significantly contributed to the prediction and design of new cocrystals by considering structural conformations and interactions energy. Whilst the insights on praziquantel polymorphs discussed in the present review will give a significant contribution to controlling their formation during manufacturing and drug formulation, the detailed multicomponent forms will help in designing and implementing future praziquantel-based functional materials. The latter will hopefully overcome praziquantel's numerous drawbacks and exploit its potential in the field of neglected tropical diseases.

Praziquantel meets Niclosamide: A dual-drug Antiparasitic Cocrystal

In this paper we report a successful example of combining drugs through cocrystallization. Specifically, the novel solid is formed by two anthelminthic drugs, namely praziquantel (PZQ) and niclosamide (NCM) in a 1:3 molar ratio, and it can be obtained through a sustainable one-step mechanochemical process in the presence of micromolar amounts of methanol. The novel solid phase crystallizes in the monoclinic space group of P21/c, showing one PZQ and three NCM molecules linked through homo- and heteromolecular hydrogen bonds in the asymmetric unit, as also attested by SSNMR and FT-IR results. A plate-like habitus is evident from scanning electron microscopy analysis with a melting point of 202.89 °C, which is intermediate to those of the parent compounds. The supramolecular interactions confer favorable properties to the cocrystal, preventing NCM transformation into the insoluble monohydrate both in the solid state and in aqueous solution. Remarkably, the PZQ - NCM cocrystal exhibits higher anthelmintic activity against in vitro S. mansoni models than corresponding physical mixture of the APIs. Finally, due to in vitro promising results, in vivo preliminary tests on mice were also performed through the administration of minicapsules size M.

Co-Crystalline Solid Solution Affords a High-Soluble and Fast-Absorbing Form of Praziquantel

Praziquantel (PZQ) is a chiral class-II drug, and it is used as a racemate for the treatment of schistosomiasis. The knowledge of several cocrystals with dicarboxylic acids has prompted the realization of solid solutions of PZQ with both enantiomers of malic acid and tartaric acid. Here, the solid form landscape of such a six-component system has been investigated. In the process, two new cocrystals were structural-characterized and three non-stoichiometric, mixed crystal forms identified and isolated. Thermal and solubility analysis indicates a fourfold solubility advantage for the newly prepared solid solutions over the pure drug. In addition, a pharmacokinetic study was conducted in rats, which involved innovative mini-capsules for the oral administration of the solid samples. The available data indicate that the faster dissolution rate of the solid solutions translates in faster absorption of the drug and helps maintain a constant steady-state concentration.

Cocrystals of Praziquantel with Phenolic Acids: Discovery, Characterization, and Evaluation

Solvent-assisted grinding (SAG) and solution slow evaporation (SSE) methods are generally used for the preparation of cocrystals. However, even by using the same solvent, active pharmaceutical ingredient (API), and cocrystal coformer (CCF), the cocrystals prepared using the two methods above are sometimes inconsistent. In the present study, in the cocrystal synthesis of praziquantel (PRA) with polyhydroxy phenolic acid, including protocatechuic acid (PA), gallic acid (GA), and ferulic acid (FA), five different cocrystals were prepared using SAG and SSE. Three of the cocrystals prepared using the SAG method have the structural characteristics of carboxylic acid dimer, and two cocrystals prepared using the SSE method formed cocrystal solvates with the structural characteristics of carboxylic acid monomer. For phenolic acids containing only one phenolic hydroxyl group (ferulic acid), when preparing cocrystals with PRA by using SAG and SSE, the same product was obtained. In addition, the weak molecular interactions that were observed in the cocrystal are explained at the molecular level by using theoretical calculation methods. Finally, the in vitro solubility of cocrystals without crystal solvents and in vivo bioavailability of PRA-FA were evaluated to further understand the influence on the physicochemical properties of API for the introduction of CCF.