Structural characterization and enantioseparation of the chiral compound praziquantel

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.

Simultaneous Determination of Esafoxolaner, Eprinomectin, Praziquantel, BHT and Their Related Substances in a Topical Finished Product by a Single Reversed-Phase High-Performance Liquid Chromatography Method

The topical product with three active pharmaceutical ingredients (APIs), namely, esafoxolaner, eprinomectin and praziquantel has demonstrated its efficacy in the treatment of cats with mixed infections with ectoparasites and nematodes and cestodes. A reversed-phase high-performance liquid chromatography (RP-HPLC) method has been developed and validated for assay and determination of related substances peaks of three APIs including the assay of antioxidant butylated hydroxytoluene (BHT) in the finished product. Analytes were separated on a short Zorbax SB-C18 column (50 × 4.6 mm I.D., 5 μm particle size, pore size: 80 Å) with gradient elution at 40 °C column temperature. Analytes were detected at 245 nm for praziquantel, esafoxolaner, eprinomectin and their degradation products. BHT and eprinomectin degradation product 8a-oxo-B1a were detected at 280 nm. All analytes of interest were adequately separated within 40 min. The assay for praziquantel, esafoxolaner, eprinomectin and BHT was conducted against their corresponding external reference standards. The related substances peaks of each API were determined by peak area and relative response factor against total peak area of their corresponding API peak in sample solution. This method has been demonstrated to be accurate, robust, specific and stability indicating.

In Vivo Evaluation of Praziquantel-Loaded Solid Lipid Nanoparticles against S. mansoni Infection in Preclinical Murine Models

This study aimed to develop and assess the long-term stability of drug-loaded solid lipid nanoparticles (SLNs). The SLNs were designed to extend the release profile, overcome the problems of bioavailability and solubility, investigate toxicity, and improve the antischistosomal efficacy of praziquantel. The aim was pursued using solvent injection co-homogenization techniques to fabricate SLNs in which Compritol ATO 888 and lecithin were used as lipids, and Pluronic F127 (PF127) was used as a stabilizer. The long-term stability effect of the PF127 as a stabilizer on the SLNs was evaluated. Dynamic light scattering (DLS) was used to determine the particle size, stability, and polydispersity. The morphology of the SLNs was examined through the use of transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The chemical properties, as well as the mechanical, thermal, and crystal behaviours of SLNs were evaluated using FTIR, ElastoSens Bio2, XRPD, DSC, and TGA, respectively. SLNs with PF127 depicted an encapsulation efficiency of 71.63% and a drug loading capacity of 11.46%. The in vitro drug release study for SLNs with PF127 showed a cumulative release of 48.08% for the PZQ within 24 h, with a similar release profile for SLNs' suspension after 120 days. DLS, ELS, and optical characterization and stability profiling data indicate that the addition of PF127 as the surfactants provided long-term stability for SLNs. In vitro cell viability and in vivo toxicity evaluation signify the safety of SLNs stabilized with PF127. In conclusion, the parasitological data showed that in S. mansoni-infected mice, a single (250 mg/kg) oral dosage of CLPF-SLNs greatly improved PZQ antischistosomal efficacy both two and four weeks post-infection. Thus, the fabricated CLPF-SLNs demonstrated significant efficiency inthe delivery of PZQ, and hence are a promising therapeutic strategy against schistosomiasis.

Praziquantel-Clays as Accelerated Release Systems to Enhance the Low Solubility of the Drug

Praziquantel is an antiparasitic drug indicated for the treatment of the schistosomiasis disease. This drug has very low aqueous solubility, requiring high oral doses for its administration which gives rise to side effects, therapeutic noncompliance and the appearance of resistant forms of the parasite. Clay minerals, like sepiolite and montmorillonite, are innocuous, non-toxic, biocompatible and low-cost excipients. Additionally, clays have high adsorbent properties that allow them to encapsulate drugs in nanometric spaces present in the channels in the case of the sepiolite or between the layers in the case of the montmorillonite. The interactions between the drug and clay minerals are studied experimentally with the strategy for preparing interactions products in organic solvents (ethanol, acetonitrile and dichloromethane) so that the interaction will be more effective and will be enhanced the aqueous solubility of praziquantel. The results showed that in the interaction products, the drug interacted with both clay minerals, which produced the loss of the crystallinity of the drug demonstrated by different techniques. This led to a significant increase in the dissolution rate of the praziquantel in all the interaction products in the simulated gastrointestinal tract media, except for the praziquantel–montmorillonite product prepared in dichloromethane that presented a controlled release in acid medium. Moreover, in vitro cytotoxicity and cell cycle studies were performed in the interaction products prepared with ethanol. The interaction product with sepiolite was biocompatible with the HTC116 line cells, and it did not produce alterations in the cell cycle. However, interaction products with montmorillonite did not produce cell death, but they showed affectation and damage of cells in the cell cycle study at the highest concentration tested (20–100 µM). Therefore, the different organic solvents used are adequate for the improvement of the biopharmaceutical profile of praziquantel. Drug–clay interaction products, specifically with sepiolite, showed very promising results in which new accelerated oral release systems of the praziquantel were obtained.

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

Praziquantel (PZQ) is a highly effective low-cost anthelmintic agent used as the first-choice treatment against schistosomiasis. The low solubility of the active is a major drawback for pharmaceutical formulation. A valid approach of the pharmaceutical industry for the improvement of the pharmacotechnical features of the active principles (such as solubility, processability, stability, among others), is the preparation of new solid forms, such as salts, polymorph, and pseudo-polymorph. Herein we report the preparation and characterization of a new solid form PZQ. The PZQ monohydrate (PZQ-MH) was prepared by a solventless procedure from the commercial racemate and the product was characterized at the solid-state employing optical digital microscopy, thermal methods (melting point, differential scanning calorimetry and thermogravimetric analysis), as well as and mid-infrared and near infrared spectroscopies. The chemical structure and content of water were full assessed by ¹H nuclear magnetic resonance (NMR) in solution. The amount of water in PZQ-was also determined by different approaches, including thermogravimetric analysis and the loss on drying test. Solid-state ¹³C NMR (ssNMR) and X-ray powder diffraction (XRPD) completed the structural characterization of the new monohydrate. PZQ-MH showed a crystalline behavior during XRPD experiments and showed relevant differences in spectroscopic, calorimetric, ssNMR and XRPD signals when it was compared with the known crystal (Form A) and amorphous forms of PZQ. The determination of the intrinsic dissolution rate (IDR) of PZQ-MH was carried out as a functional characterization, observing that the new form had slightly higher IDR than Form A.

Praziquantel-Solid Lipid Nanoparticles Produced by Supercritical Carbon Dioxide Extraction: Physicochemical Characterization, Release Profile, and Cytotoxicity

Solid lipid nanoparticles (SLNs) can be produced by various methods, but most of them are difficult to scale up. Supercritical fluid (SCF) is an important tool to produce micro/nanoparticles with a narrow size distribution and high encapsulation efficiency. The aim of this work was to produce cetyl palmitate SLNs using SCF to be loaded with praziquantel (PZQ) as an insoluble model drug. The mean particle size (nm), polydispersity index (PdI), zeta potential, and encapsulation efficiency (EE) were determined on the freshly prepared samples, which were also subject of Differential Scanning Calorimetry (DSC), Fourier-Transform Infrared Spectroscopy (FTIR), drug release profile, and in vitro cytotoxicity analyses. PZQ-SLN exhibited a mean size of ~25 nm, PdI ~ 0.5, zeta potential ~−28 mV, and EE 88.37%. The DSC analysis demonstrated that SCF reduced the crystallinity of cetyl palmitate and favored the loading of PZQ into the lipid matrices. No chemical interaction between the PZQ and cetyl palmitate was revealed by FTIR analysis, while the release or PZQ from SLN followed the Weibull model. PZQ-SLN showed low cytotoxicity against fibroblasts cell lines. This study demonstrates that SCF may be a suitable scale-up procedure for the production of SLN, which have shown to be an appropriate carrier for PZQ.

Conformational polymorphic changes in the crystal structure of the chiral antiparasitic drug praziquantel and interactions with calcium carbonate

Praziquantel is an antiparasitic drug used for decades. Currently, the praziquantel commercial preparation is a racemic mixture, in which only the levo-enantiomer possesses anthelmintic activity. The knowledge of its properties in the solid state and other chemical-physical properties is necessary for improving its efficacy and applications. Drug solid dispersions were prepared with calcium carbonate at 1:5 drug to excipient weight ratio by solvent evaporation method. Then, the modification of the crystal structure of the racemic polymorph of praziquantel in presence of calcium carbonate has been studied by means of several analytical techniques (DSC, TGA, XRD, SEM, FTIR, Raman spectroscopy and chiral liquid chromatography). This study has been completed with atomistic calculations based on empirical interatomic force fields and quantum mechanics methods applied to the crystal structure of praziquantel and of intermolecular interactions. The results evidenced that calcium carbonate provoked a conformational change in the praziquantel molecule yielding the formation of different polymorphs of praziquantel crystal. These alterations were not observed replacing calcium carbonate with colloidal silica as excipient in the solid dispersion.

A new soluble and bioactive polymorph of praziquantel

Praziquantel is the only available drug to treat Schistosomiasis. However, its utilization is limited by many drawbacks, including the high therapeutic dose needed, resulting in large tablets and capsules difficult to be swallowed, especially from pediatric patients. In this study, an alternative option to overcome these disadvantages is proposed: to switch to a novel crystalline polymorph of racemic compound praziquantel. The preparation of the crystalline polymorph was realized via a neat grinding process in a vibrational mill. The new phase (Form B) was chemically identical to the starting material (as proved by HPLC, ¹H NMR, and polarimetry), but showed different physical properties (as evaluated by SEM, differential scanning calorimetry, thermogravimetry, ATR-FTIR spectroscopy, X-ray powder diffraction, and solid-state NMR). Furthermore, the crystal structure of the new phase was solved from the powder synchrotron X-ray diffraction pattern, resulting in a monoclinic C2/c cell and validated by DFT-D calculation. Moreover the simulated solid-state NMR ¹³C chemical shifts were in excellent agreement with the experimental data. The conversion of original praziquantel into Form B showed to affect positively the water solubility and the intrinsic dissolution rate of praziquantel. Both the in vitro and in vivo activity against Schistosoma mansoni were maintained. Our findings suggest that the new phase, that proved to be physically stable for at least one year, is a promising product for designing a new praziquantel formulation.

An explorative analysis of process and formulation variables affecting comilling in a vibrational mill: The case of praziquantel

Praziquantel, a BCS II class anthelmintic drug used for the treatment of schistosome infections, was coground in a vibrational mill with different polymers (linear and crosslinked povidone, copovidone and sodium starch glycolate). An explorative analysis of formulation variables (drug-polymer wt ratio and polymer type) and process parameters (type of grinding media, grinding time and frequency) was carried out with the help of an experimental screening design. The influence of the above mentioned factors on three PZQ characteristics (residual crystallinity, water solubility enhancement and drug recovery) was studied. The variation of carrier amount proved to be by far the most important variable affecting all the experimental responses. A lower impact and, in some cases, rather null effect, had the variation of the process variables. All coground systems were characterized by a high amorphous degree and a solubility significantly higher than the API. A very promising product was obtained by processing at 20Hz for 4h, using 3 spheres of 15mm as grinding media, i.e. a coground having a 50% API content, showing a 4.6-fold greater solubility at 20°C than pure praziquantel. This product maintained the same antischistosomal activity of pure API and was both physically and chemically stable for at least 6 months.

Validated capillary electrophoretic method for the enantiomeric quality control of R-praziquantel

The enantiomers of praziquantel, the drug of choice in schistosomiasis, were separated by electrokinetic chromatography with cyclodextrins. Nine anionic cyclodextrins were screened for their ability to discriminate between the uncharged enantiomers. Seven investigated selectors presented chiral interactions with the enantiomers, these cases being interpreted in terms of stability constants and complex mobilities. The best results were delivered by sulfated-β-cyclodextrin, where quasi-equal stability constants were accompanied by extreme selectivity values and was explained on the basis of highly different mobilities of the transient diastereomeric complexes. Since the enantiomer migration order was unfavorable, a simple polarity switch was employed (detection end at anode), which apart from migration order reversal, also resulted in extreme resolution values (R_s > 35) and increased migration times. After optimization (50 mM phosphate buffer pH 2.0, supplied with 15 mM sulfated-β-cyclodextrin, 15 kV, capillary temperature 25°C, short-end injection with 50 mbar × 2 s), analysis time under 10 min were obtained, while still maintaining high resolution (R_s > 10). The method was validated according to the ICH guidelines and application of the method was tested on in-house synthetized R-praziquantel batches and on commercial, combination tablets containing racemic mixture of the drug.

Molecular modeling and infrared and Raman spectroscopy of the crystal structure of the chiral antiparasitic drug Praziquantel

Anthelmintic praziquantel (PZQ) and its molecular and crystal lattice structures were studied by means of atomistic calculations based on empirical interatomic potentials and quantum mechanical methods (DFT). This chiral drug presents several crystal polymorphs due to the enantiomers (either R or S) or the racemic crystal, and different molecular conformations. The relative configurations of the carbonyl groups in PZQ define these conformations that produce different polymorphs. The polarity of these conformers is quite different and their relative population can vary in media with different polarity. Crystal structures of PZQ were studied by infrared and Raman spectroscopy and their spectroscopical properties were calculated by quantum mechanical methods, assigning many of their bands, and finding a good agreement with experimental data.

Development of flexible and dispersible oral formulations containing praziquantel for potential schistosomiasis treatment of pre-school age children

Praziquantel (PZQ), an anthelmintic drug used in developing countries for the treatment of schistosome infections, was processed using the fluid bed wet granulation technology to prepare fast dispersible granules, as an appropriate and flexible dosage form for pre-school-aged children. Granulation experiments were performed incorporating PZQ either in the powder mixture, according to the traditional way, or in the liquid phase containing wetting agents. In the powder mixture several excipients were tested: Flowlac 100 as filler, Galeniq 721 (isomalt) and Neosorb P 100 T (D-sorbitol) as sweeteners and PVP K30 as binder; while in the liquid phase Lutrol F68, Cremophor RH 40 or Tween 80 as surfactants were investigated. Different formulations loaded with 10% w/w (batches 1-8) and 20% w/w of PZQ (batches 9-13) were produced The majority of granules displayed good flow properties and uniform drug content. X-ray powder diffraction showed that PZQ remained in its original crystalline state, while differential scanning calorimetry and Fourier transform-infrared analysis evidenced the formation of chemical interactions among the ingredients. The solubilisation test performed in non-sink condition to reproduce the actual condition in which a child of 4 years takes the medicine revealed that granules quickly formed a very fine suspension in water (dV90=39.9 μm). Although after the granulation process the solubility of raw PZQ was not increased, adding the aqueous suspension to 500 ml of buffer solution of pH 1.5, simulating the fasted state of a child, 50% of the drug was dissolved after 30 min. After granule manipulation with milk and fruit juices, no PZQ degradation was observed during time. Finally, the selected granule formulation provided evidence to be stable even at hot and very humid climate (30°C/75% RH), at least for the examined time.

Intestinal Lymphatic Delivery of Praziquantel by Solid Lipid Nanoparticles: Formulation Design,In VitroandIn VivoStudies

The aim of the present work was to design and develop Praziquantal (PZQ) loaded solid lipid nanoparticles (PZQ-SLN) to improve the oral bioavailability by targeting intestinal lymphatic system. PZQ is practically insoluble in water and exhibits extensive hepatic first-pass metabolism. PZQ SLN were composed of triglycerides, lecithin and various aqueous surfactants; were optimized using hot homogenization followed by ultrasonication method. The optimized SLN had particle size of123±3.41 nm, EE of86.6±5.72%. The drug release of PZQ-SLN showed initial burst release followed by the sustained release. Inspite of zeta potential being around −10 mV, the optimized SLN were stable at storage conditions (5±3°C and25±2°C/60±5% RH) for six months. TEM study confirmed the almost spherical shape similar to the control formulations. Solid state characterization using differential scanning calorimeter (DSC) and powder X-ray diffraction (PXRD) analysis confirmed the homogeneous distribution of PZQ within the lipid matrix. The 5.81-fold increase inAUC0→∞, after intraduodenal administration of PZQ-SLN in rats treated with saline in comparison to rats treated with cycloheximide (a blocker of intestinal lymphatic pathway), confirmed its intestinal lymphatic delivery. The experimental results indicate that SLN may offer a promising strategy for improving the therapeutic efficacy and reducing the dose.

Solid dispersions with hydrogenated castor oil increase solubility, dissolution rate and intestinal absorption of praziquantel

The solubility behavior of drugs remains one of the most challenging aspects in formulation development. Solid Dispersion (SD) has tremendous potential for improving drug solubility. Although praziquantel (PZQ) is the first drug of choice in the treatment of schistosomiasis, its poor solubility has restricted its delivery oral route. In spite of its poor solubility, PZQ is well absorbed in the gastrointestinal tract, but large doses are required to achieve adequate concentration at the target sites. The aim of this study was to improve the solubility and dissolution rate of PZQ and to evaluate its intestinal absorption. SDs were formulated with PEG-60 castor oil hydrogenated (CR-60) using a fusion and evaporation method. Pure PZQ and physical mixtures (PM) and PZQ-CR-60 (2:1; 1:1; 1:2 ratios) were compared as regards their solubility, dissolution and intestinal absorption. The experimental results demonstrated the improvement in the solubility, dissolution rate and intestinal absorption. In addition, the solubility behavior showed pH dependency and that the solubility of PZQ was slower in acidic medium than in neutral and basic mediums. The increase in PZQ solubility of the SD with the CR-60 could be attributed to several factors such as improved wettability, local solubilization, drug particle size reduction and crystalline or, interstitial solid solution reduction.

Complexation and Chiral Drug Recognition of an Amphiphilic Phenothiazine Derivative with β‐Cyclodextrin

Promethazine hydrochloride (PTZ) is an amphiphilic drug derived from the phenothiazine structure that possesses a charged aliphatic chain with a chiral carbon. In the presence of beta-cyclodextrin (beta-CD), this drug undergoes significant changes of its photophysical properties in aqueous solution. Fluorescence spectroscopy measurements show the formation of a 1:1 stoichiometry complex with quantum yield lower than that of the pure PTZ, and two fluorescence lifetimes, which can be assigned to the free and complexed forms of the drug. In addition, (1)H NMR spectra, and 2D rotating-frame Overhauser enhancement spectroscopy (ROESY) were used to characterize the drug and the complex, and to determine the effects of the complexation on the aggregation. For the drug binary system, a noncooperative association process is observed, and in the presence of macrocycle, the chemical shifts reveal a chiral resolution of the drug enantiomers, with different stability constants of the complexes. beta-CD modifies the aggregation of PTZ in an extension that confirms the formation of a 1:1 complex. ROE enhancements and molecular modeling strategies show the most likely structure of the complex in solution, in which one of the phenyl rings is buried into the CD cavity, with a slight inclusion of the aliphatic part.

Evaluation of melt granulation and ultrasonic spray congealing as techniques to enhance the dissolution of praziquantel

Praziquantel (PZQ), an anthelminthic drug widely used in developing countries, is classified in Class II in the Biopharmaceutics Classification Systems; this means that PZQ has very low water solubility and high permeability, thus the dissolution is the absorption rate-limiting factor. The aim of this work was to evaluate the suitability of melt granulation and ultrasonic spray congealing as techniques for enhancing the dissolution rate of PZQ. Granules in high shear mixer were prepared by melt granulation, using polyethylene glycol 4000 or poloxamer 188 as meltable binders and alpha-lactose monohydrate as a filler. Quite regularly shaped granules having main size fraction in the range 200-500 microm were obtained using both formulations; however, only poloxamer 188 granules demonstrated a significant (P=0.05) increase of the PZQ dissolution rate compared to pure drug. To evaluate the potential of ultrasonic spray congealing, Gelucire 50/13 microparticles having different drug to carrier ratios (5, 10, 20 and 30%, w/w) were then prepared. The results showed that all the microparticles had a significant higher dissolution rate (P=0.05) respect to pure PZQ. The increase of the PZQ content considerably decreased the dissolution rate of the drug: 5 and 10% PZQ loaded systems evidenced dissolution significantly enhanced compared to 20 and 30% PZQ microparticles. The microparticle's characterisation, performed by Differential Scanning Calorimetry, Hot Stage Microscopy, X-ray powder diffraction and FT-Infrared analysis, evidenced the absence of both modifications of the solid state of PZQ and of significant interactions between the drug and the carrier. In conclusion, melt granulation and ultrasonic spray congealing could be proposed as solvent free, rapid and low expensive manufacturing methods to increase the in vitro dissolution rate of PZQ.

Investigation of the phase diagrams of chiral praziquantel

In the present work, thermal properties of praziquantel, including melting point phase diagram and solubility, were determined for the purpose of exploration on an integrated enantioseparation process of chromatography and crystallization. The solubility of racemic praziquantel in methanol and 2-propanol was measured in the temperature range between 0 and 40 degrees C. In agreement with previous conclusions, the resulting phase diagram reveals the racemic compound behavior of praziquantel arising from the existence of eutectics. A ternary phase diagram of praziquantel enantiomers and the methanol system was also determined. Based on the information provided by the ternary solubility phase diagram, an optimized integrated enantioseparation process was suggested. Pure praziquantel crystals were recovered, and the crystal structure was solved by X-ray crystallography.