Screening of conformational polymorphism of ibuprofen in supercritical CO 2

Amorphous stabilization of BCS II drugs using mesoporous silica

This study aimed to investigate the amorphous stabilization of BCS Class II drugs using mesoporous silica as a carrier to produce amorphous solid dispersions. Ibuprofen, fenofibrate, and budesonide were selected as model drugs to evaluate the impact of molecular weight and partition coefficient on the solid state of drug-loaded mesoporous silica (MS) particles. The model drugs were loaded into three grades of MS, SYLYSIA SY730, SYLYSIA SY430, and SYLYSIA SY350, with pore diameters of 2.5 nm, 17 nm, and 21 nm, respectively, at 1:1, 2:1, and 3:1, carrier to drug ratios, and three different loading concentrations using solvent immersion and spray drying techniques. Differential scanning calorimetry (DSC) thermograms of SY430 and SY350 samples exhibited melting point depressions indicating constricted crystallization inside the pores, whereas SY730 samples with melting points matching the pure API may be a result of surface crystallization. Powder x-ray diffraction (PXRD) diffractograms showed all crystalline samples matched the diffraction patterns of the pure API indicating no polymorphic transitions and all 3:1 ratio samples exhibited amorphous halo profiles. Response surface regression analysis and Classification and Regression Tree (CART) analysis suggest carrier to drug ratios, followed by molecular weight, have the most significant impact on the crystallinity of a drug loaded into MS particles.

Modeling of the Aqueous Solubility of N-butyl-N-methyl-1-phenylpyrrolo[1,2-a] pyrazine-3-carboxamide: From Micronization to Creation of Amorphous-Crystalline Composites with a Polymer

N-butyl-N-methyl-1-phenylpyrrole[1,2-a] pyrazine-3-carboxamide (GML-3) is a potential candidate for combination drug therapy due to its anxiolytic and antidepressant activity. The anxiolytic activity of GML-3 is comparable to diazepam. The antidepressant activity of GML-3 is comparable to amitriptyline. GML-3 is an 18 kDa mitochondrial translocator protein (TSPO) ligand and is devoid of most of the side effects of diazepam, which makes the research on the creation of drugs based on it promising. However, its low water solubility and tendency to agglomerate prevented its release. This research aimed to study the effect of dry grinding, the rapid expansion of a supercritical solution (RESS), and the eutectic mixture (composite) of GML-3 with polyvinylpyrrolidone (PVP) on the particle size, dissolution rate, and lattice retention of GML-3. The use of supercritical CO2 in the RESS method was promising in terms of particle size reduction, resulting in a reduction in the particle size of GML-3 to 20-40 nm with a 430-fold increase in dissolution rate. However, in addition to particle size reduction after RESS, GML-3 began to show signs of a polymorphism phenomenon, which was also studied in this article. It was found that coarse grinding reduced particle size by a factor of 2 but did not significantly affect solubility or crystal structure. Co-milling with the polymer made it possible to level the effect of the appearance of a residual electrostatic charge on the particles, as in the case of grinding, and the increased solubility in the resulting mechanical mixtures of GML-3 with the polymer may also indicate the dissolving properties of polymers (an increase in 400-800 times). The best result in terms of GML-3 solubility was demonstrated by the resulting GML-3:PVP composite at a ratio of 1:4, which made it possible to achieve a solubility of about 80% active pharmaceutical ingredient (API) within an hour with an increase in the dissolution rate by 1600 times. Thus, the creation of composites is the most effective method for improving the solubility of GML-3, superior to micronization.

Molecular Mechanism of Conformational Crossover of Mefenamic Acid Molecules in scCO2

In this work, we studied conformational equilibria of molecules of mefenamic acid in its diluted solution in scCO₂ under isochoric heating conditions in the temperature range of 140-210 °C along the isochore corresponding to the scCO₂ density of 1.1 of its critical value. This phase diagram range totally covers the region of conformational transitions of molecules of mefenamic acid in its saturated solution in scCO₂. We found that in the considered phase diagram region, the equilibrium of two conformers is realized in this solution. In the temperature range of 140-180 °C, conformer I related to the first, most stable polymorph of mefenamic acid prevails. In the temperature range of 200-210 °C, conformer II, which is related to the second metastable polymorph becomes dominant. Based on the results of quantum chemical calculations and experimental IR spectroscopy data on the mefenamic acid conformer populations, we classified this temperature-induced conformational crossover as an entropy-driven phenomenon.

Conformational Screening of Arbidol Solvates: Investigation via 2D NOESY

Understanding of the nucleation process's fundamental principles in saturated solutions is an urgent task. To do this task, it is necessary to control the formation of polymorphic forms of biologically active compounds. In certain cases, a compound can exist in a single polymorphic form, but have several solvates which can appear in different crystal forms, depending on the medium and conditions of formation, and show different pharmaceutical activity. In the present paper, we report on the analysis of Arbidol conformational preferences in two solvents of different polarities-deuterated chloroform and dimethyl sulfoxide-at 25 °C, using the 2D NOESY method. The Arbidol molecule has various solvate forms depending on the molecular conformation. The method based on the nuclear Overhauser effect spectroscopy was shown to be efficient in the analysis of complex heterocyclic compounds possessing conformation-dependent pseudo-polymorphism. It is one of the types of polymorphism observed in compounds forming crystal solvates. Combined use of NMR methods and X-ray data allowed determining of conformer populations of Arbidol in CDCl₃ and DMSO-d₆ which were found to be 8/92% and 37/63%, respectively. The preferred conformation in solution is the same that appears in stable crystal solvates of Arbidol.

Transformation under pressure: Discovery of a novel crystalline form of anthelmintic drug Praziquantel using high-pressure supercritical carbon dioxide

Supercritical carbon dioxide (CO₂) has been used as a processing technique to control polymorphism of pharmaceuticals. However, there are fewer reports of novel polymorphs being discovered by supercritical CO₂ processing. As supercritical crystallization methods gain attention for potential in pharmaceutical processing, they may become a critical screening tool for discovery of new polymorphs. In this work, a case study is presented for a novel crystalline form of the anthelmintic drug, Praziquantel, found through supercritical CO₂ processing. The novel form of Praziquantel was characterized by chromatography, nuclear magnetic resonance and infrared spectroscopy, X-ray powder diffraction, thermal analysis, and scanning electron microscopy. Furthermore, the novel form exhibited 13-20% improved solubility compared to commercial Form A between pH 1.6 and 7.5 and was physically stable under stressed conditions (40 °C and 75% relative humidity) for 7.5 weeks. Overall, this work showed that supercritical CO₂ processing is a valuable tool to screen for novel, and possibly viable polymorphs of pharmaceutical compounds with improved properties.

Ibuprofen loaded centrifugally spun microfibers for quick relief of inflammation in rats

The conventional dosage forms (tablets, capsules), of ibuprofen has less potential in suppression of pain and inflammation due to their slow dissolution rates and lower bioavailability. Aim of this study was to fabricate fibrous solid dispersion of ibuprofen for improved dissolution rate and quick therapeutic action. Drug loaded microfibers were fabricated using centrifugal melt spinning (CMS) technique from the physical mixture of sucrose, ibuprofen and a hydrophilic polymer, PVP. These fibers were characterized by SEM, PXRD, DSC, and FTIR spectroscopy. The selected formulation was also pressed into tablets by direct compression method followed by its in-vitro and in-vivo characterization. The production yield of fibers was 75 ± 2% with an average diameter 15 ± 5 µm. The drug loading efficiency (DLE) was 85 ± 5%. The tablets dissolved rapidly (<40s). In-vitro dissolution studies have shown >85% of ibuprofen dissolved from tablet within first 2 min which was ∼5 times quicker than drug alone. Dissolution efficiency has improved from 0.63 of ibuprofen to 0.95 of that in fibers with ∼7 times reduction in mean dissolution time. PXRD, andDSC have shown amorphous state of ibuprofen in the formulation and FTIR spectra demonstrated no interaction of drug with excipients . In-vivo anti-inflammatory studies using rabbits revealed a significant (p <0.05) reduction in paw volume (mm) in the groups treated with fibrous formulation. This study concludes that microfibers produced by centrifugal melt spinning has improved dissolution rates and bioavailability of ibuprofen. Incorporation of polymer in the formulations improves the production yield and drug loading efficiency of microfibers.

Exposing Hidden Conformations of Carbamazepine Appearing Due to Interaction With the Solid Phase by 2D 1H-15N HMBC NMR Spectroscopy

Two-dimensional ¹H-¹⁵N HMBC NMR spectra of the well-known anticonvulsant carbamazepine dissolved in different organic solvents, recorded on an NMR spectrometer prove the existence of hidden conformers in saturated solutions. Obtained conformer distribution arises due to the presence of the solid phase in saturated solution. A weak influence of ring currents was revealed for different molecular conformations of carbamazepine dissolved in a saturated solution, which provides a simple approach to discovering hidden conformations. Hidden conformers were found in three different solvents: dimethyl sulfoxide, chloroform, and dichloromethane.

Experimental Investigation and CFD Modeling of Supercritical Adsorption Process

The kinetics of the supercritical adsorption process was experimentally studied by the example of ”ibuprofen-silica aerogel” composition obtainment at various parameters: Pressure 120–200 bar and temperature 40–60 °C. Computational Fluid Dynamics (CFD) model of the supercritical adsorption process in a high-pressure apparatus based on the provisions of continuum mechanics is proposed. Using supercritical adsorption process kinetics experimental data, the dependences of the effective diffusion coefficient of active substance in the aerogel, and the maximum amount of the adsorbed active substance into the aerogel on temperature and pressure are revealed. Adequacy of the proposed model is confirmed. The proposed mathematical model allows predicting the behavior of system (fields of velocity, temperature, pressure, composition, density, etc.) at each point of the studied medium. It makes possible to predict mass transport rate of the active substance inside the porous body depending on the geometry of the apparatus, structure of flow, temperature, and pressure.

Polymorphs and pharmacokinetics of an antipsychotic drug candidate

A potent antipsychotic drug candidate, 7-(4-(4-(6-fluorobenzo[d]-isoxazol-3-yl)-piperidin-1-yl)butoxy)-4-methyl-8-chloro -2H-chromen-2-one mesylate(CY611), with good in vitro and in vivo antipsychotic effects was investigated for preformulation evaluation by crystallography methods. Three anhydrous polymorphs(Form I-III), a monohydrate(Form IV), and a NMP solvate(Form V) were discovered and characterized by powder X-ray diffraction, thermal analysis, attenuated total reflection-fourier transform infrared spectroscopy and scanning electron microscopy. Form I, monohydrate Form IV, and a NMP solvate Form V of the drug candidate were isolated, and their structures were determined by single crystal X-ray diffraction. IDR and relative stability experiment were performed. Although Form II has the fastest release rate in water, it easy transformed to monohydrate which has the lowest release rate. In vivo pharmacokinetic study showed that the Form III has the highest bioavailability at 35.4%. Considering the balance between the physicochemical properties, bioavailability and manufacturability of the available polymorphs, Form III may be the optimal form candidate for the eventual formulation.

Conformational equilibria of pharmaceuticals in supercritical CO2, IR spectroscopy and quantum chemical calculations

In this work we demonstrate a self-consistent effective technique of analyzing the conformational equilibria of active pharmaceutical ingredient (API) molecules dissolved in supercritical carbon dioxide in a wide range of thermodynamic parameters of state. This approach can be useful for pharmaceutics when the crystalline forms of pharmaceuticals with a high purity degree and desirable polymorphism are produced using CO₂-based supercritical fluids technologies. Within this approach we use a combination of quantum chemical calculations and in situ IR spectroscopy. Quantum chemical calculations allow us to perform the initial conformational search and to determine the energy characteristics of the most stable conformers of API and the energy barriers of transitions between them. IR spectroscopy gives the information on the equilibrium of the most stable conformers of pharmaceuticals dissolved in scCO₂ in the thermodynamic parameter range of interest. Finally we validate our approach by applying it to the study of carbamazepine dissolved in scCO₂ being in permanent contact with an excess of crystalline carbamazepine as an example. The conformational search for carbamazepine molecules in scCO₂ was also performed using molecular dynamics simulation for comparison with the results obtained by the technique presented in this paper.

Application of Chemometrics Approaches to Analysis of Mid-Infrared Spectra of Ibuprofen Diluted in Supercritical Carbon Dioxide

This work represents a comprehensive analysis of mid-infrared (mid-IR) spectra of ibuprofen diluted in supercritical CO₂ (in the temperature range of 40-90 ℃ and at the CO₂ density corresponding to 1.3 of its critical value). The study employed mathematical approaches based on data matrix analysis such as two-dimensional cross-correlation analysis (2D-COS) and principal component analysis (PCA). Two-dimensional cross-correlation analysis allowed us to reveal correlations between the spectral contributions constituting the analytical spectral band and assigned to certain ibuprofen conformers, as well as the significance of these correlations. It has been shown that the considerable increase in the total intensity of the analytical spectral band, proportional to the equilibrium ibuprofen concentration in the supercritical CO₂ phase, is accompanied by certain redistribution of intensities of the spectral components related to the corresponding conformers. The PCA allowed us to determine the changes of intensities of individual spectral contributions for each thermodynamic point in the considered temperature range. It has been shown that these two complementary methods provide more precise information that may be used as the initial data in the classical analysis of spectral data based on spectral curve deconvolution into individual spectral contributions.