Preparation and characterization of a new solid form of praziquantel, an essential anthelmintic drug. Praziquantel racemic monohydrate

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.

Comparing and Quantifying the Efficiency of Cocrystal Screening Methods for Praziquantel

Pharmaceutical cocrystals are highly interesting due to their effect on physicochemical properties and their role in separation technologies, particularly for chiral molecules. Detection of new cocrystals is a challenge, and robust screening methods are required. As numerous techniques exist that differ in their crystallization mechanisms, their efficiencies depend on the coformers investigated. The most important parameters characterizing the methods are the (a) screenable coformer fraction, (b) coformer success rate, (c) ability to give several cocrystals per successful coformer, (d) identification of new stable phases, and (e) experimental convenience. Based on these parameters, we compare and quantify the performance of three methods: liquid-assisted grinding, solvent evaporation, and saturation temperature measurements of mixtures. These methods were used to screen 30 molecules, predicted by a network-based link prediction algorithm (described in Cryst. Growth Des. 2021, 21(6), 3428-3437) as potential coformers for the target molecule praziquantel. The solvent evaporation method presented more drawbacks than advantages, liquid-assisted grinding emerged as the most successful and the quickest, while saturation temperature measurements provided equally good results in a slower route yielding additional solubility information relevant for future screenings, single-crystal growth, and cocrystal production processes. Seventeen cocrystals were found, with 14 showing stability and 12 structures resolved.

Active pharmaceutical ingredients (APIs) in ionic liquids: An effective approach for API physiochemical parameter optimization

Ionic liquids (ILs) are widely used as solvents, co-solvents and permeation enhancers in the biomedical and pharmaceutical fields. There are many advantages to using active pharmaceutical ingredients (APIs) in the production of ILs for drug delivery, including the ability to tailor solubility, improve thermal stability, increase dissolution, regulate drug release, improve API permeability, and modulate cytotoxicity on tumor cells. Such an approach has shown significant potential as a tool for drug delivery. As a result, APIs converted into ILs are used as active components in solutions, emulsions, and even nanoparticles (NPs). In this review, we explore the use and physiochemical characteristics of APIs via ILs, including improvements of their physicochemical properties in preformulation and formulation development.

Nanoconfinement of a Pharmaceutical Cocrystal with Praziquantel in Mesoporous Silica: The Influence of the Solid Form on Dissolution Enhancement

Nanoconfinement is a recent strategy to enhance solubility and dissolution of active pharmaceutical ingredients (APIs) with poor biopharmaceutical properties. In this work, we combine the advantage of cocrystals of racemic praziquantel (PZQ) containing a water-soluble coformer (i.e., increased solubility and supersaturation) and its confinement in a mesoporous silica material (i.e., increased dissolution rate). Among various potential cocrystalline phases of PZQ with dicarboxylic acid coformers, the cocrystal with glutaric acid (PZQ-GLU) was selected and successfully loaded by the melting method into nanopores of SBA-15 (experimental pore size of 5.6 nm) as suggested by physical and spectroscopic characterization using various complementary techniques like N₂ adsorption, powder X-ray diffraction (PXRD), infrared spectroscopy (IR), solid-state NMR (ss-NMR), differential scanning calorimetry (DSC), and field emission-scanning electron microscopy (FE-SEM) analysis. The PZQ-GLU phase confined in SBA-15 presents more mobility according to ss-NMR studies but still retains its cocrystal-like features in the IR spectra, and it also shows depression of the melting transition temperature in DSC. On the contrary, pristine PZQ loaded into SBA-15 was found only in the amorphous state, according to the aforementioned studies. This dissimilar behavior of the composites was attributed to the larger crystal lattice of PZQ over the PZQ-GLU cocrystal (3320.1 vs 1167.9 ų) and to stronger intermolecular interactions between PZQ and GLU, facilitating the confinement of a more mobile solid-like phase in the constrained channels. Powder dissolution studies under extremely nonsink conditions (SI = 0.014) of the confined PZQ-GLU and amorphous PZQ phases embedded in mesoporous silica showed transient supersaturation behavior when dissolving in simulated gastric fluid (HCl pH 1.2 at 37 ± 0.5 °C) in a similar fashion to the bare cocrystal PZQ-GLU. A comparison of the area under the curve (AUC_0-90 min) of the dissolution profiles afforded a dissolution advantage of 2-fold (p < 0.05) of the new solid phases over pristine racemic PZQ after 90 min; under these conditions, the solubilized API reprecipitated as the recently discovered PZQ hemihydrate (PZQ-HH). In the presence of a cellulosic polymer, sustained solubilization of PZQ from composites SBA-15/PZQ or SBA-15/PZQ-GLU was observed, increasing AUC_0-90 min up to 5.1-fold in comparison to pristine PZQ. The combination of a confined solid phase in mesoporous silica and a methylcellulose polymer in the dissolution medium effectively maintained the drug solubilized during times significant to promote absorption. Finally, powder dissolution studies under intermediate nonsink conditions (SI = 1.99) showed a fast release profile from the nanoconfined PZQ-GLU phase in SBA-15, which reached rapid saturation (95% drug dissolved at 30 min); the amorphous PZQ composite and bare PZQ-GLU also displayed an immediate release of the API but at a lower rate (69% drug dissolved at 30 min). In all of these cases, a large dissolution advantage was observed from any of the novel solid phases over PZQ.

Ionic liquids as a useful tool for tailoring active pharmaceutical ingredients

Ionic liquids (ILs) have been widely used in biomedical and pharmaceutical fields as solvents or permeation enhancers. Recently, more and more researchers focused on optimizing the physicochemical properties of active pharmaceutical ingredient (API) by ILs technology. Converting APIs into ILs (API-ILs) has shown great potential for drug delivery by eliminating polymorphism, tailoring solubility, improving thermal stability, increasing dissolution, controlling drug release, modulating the surfactant properties, enhancing permeability of APIs and modulating cytotoxicity on tumor cells. In addition, API-ILs are also used in various formulations as active ingredients, such as solutions, emulsions, even tablets or nanoparticles. This paper aims to review current status of API-ILs, including the rational and design, preparation and characterization, the improvement on the physicochemical characteristics of APIs, the compatibility of API-ILs with various formulations, and the future prospects of API-ILs in biomedical and pharmaceutical fields.

Cocrystals of Praziquantel: Discovery by Network-Based Link Prediction

Cocrystallization has been promoted as an attractive early development tool as it can change the physicochemical properties of a target compound and possibly enable the purification of single enantiomers from racemic compounds. In general, the identification of adequate cocrystallization candidates (or coformers) is troublesome and hampers the exploration of the solid-state landscape. For this reason, several computational tools have been introduced over the last two decades. In this study, cocrystals of Praziquantel (PZQ), an anthelmintic drug used to treat schistosomiasis, are predicted with network-based link prediction and experimentally explored. Single crystals of 12 experimental cocrystal indications were grown and subjected to a structural analysis with single-crystal X-ray diffraction. This case study illustrates the power of the link-prediction approach and its ability to suggest a diverse set of new coformer candidates for a target compound when starting from only a limited number of known cocrystals.

Mechanochemical Formation of Racemic Praziquantel Hemihydrate with Improved Biopharmaceutical Properties

Praziquantel (PZQ) is the first-line drug used against schistosomiasis, one of the most common parasitic diseases in the world. A series of crystalline structures including two new polymorphs of the pure drug and a series of cocrystals of PZQ have been discovered and deposited in the Cambridge Structural Database (CSD). This work adds to the list of multicomponent forms of PZQ a relevant example of a racemic hemihydrate (PZQ-HH), obtainable from commercial PZQ (polymorphic Form A) through mechanochemistry. Noteworthy, the formation of the new hemihydrate strongly depends on the initial polymorphic form of PZQ and on the experimental conditions used. The new PZQ-HH has been fully characterized by means of HPLC, Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), Hot-Stage Microscopy (SEM), Powder X-Ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), FT-IR, polarimetry, solid-state NMR (SS-NMR), solubility and intrinsic dissolution rate (IDR), and in vitro tests on Schistosoma mansoni adults. The crystal structure was solved from the powder X-ray diffraction pattern and validated by periodic-DFT calculations. The new bioactive hemihydrate was physically stable for three months and showed peculiar biopharmaceutical features including enhanced solubility and a double intrinsic dissolution rate in water in comparison to the commercially available PZQ Form A.