Correlating Single Crystal Structure, Nanomechanical, and Bulk Compaction Behavior of Febuxostat Polymorphs

Trace polymer coated clarithromycin spherulites: Formation mechanism, improvement in pharmaceutical properties and development of high-drug-loading direct compression tablets

Clarithromycin (CLA) is a high dose antibiotic drug exhibiting poor flowability and tabletability, making the tablet development challenging. This study aims to develop spherulitic CLA by introducing trace amount of polymer in crystallization solution. Its formation mechanism, physicochemical properties and potential for the direct compression (DC) tablets development were also investigated. Morphological analyses and the in situ observation on crystallization process revealed that the CLA spherulites are formed by fractal branching growth from both sides of the threadlike precursor fibers. 1H NMR analysis and nucleation time monitoring indicated that the existence of hydroxypropyl cellulose in solution slowed down the crystal nucleation and growth rate by forming hydrogen bonding interactions with CLA molecules, making the system maintain high supersaturation, providing high driving forces for CLA spherulitic growth. In comparison to commercial CLA, the CLA spherulites exhibit profoundly improved flowability, tabletability and dissolution behaviors. XPS, contact angle and Raman mapping analysis confirmed the presence of a thin HPC layer on the surfaces and interior of CLA spherulitic particles, resulting in increasing powder plasticity, interparticulate bonding strength and powder wettability, thus better tabletability and dissolution performances. The improved flowability and tabletability of CLA spherulites also enabled the successful development of DC tablet formulation with a high CLA loading (82.8 wt%) and similar dissolution profiles to reference listed drug. This study provides a novel solid form of CLA with superior manufacturability for further development.

Recent Advances in Nanomechanical Measurements and Their Application for Pharmaceutical Crystals

Mechanical behavior of pharmaceutical crystals directly impacts the formulation development and manufacturing of drug products. The understanding of crystal structure-mechanical behavior of pharmaceutical and molecular crystals has recently gained substantial attention among pharmaceutical and materials scientists with the advent of advanced nanomechanical testing instruments like nanoindentation. For the past few decades, instrumented nanoindentation was a popular technique for measuring the mechanical properties of thin films and small-length scale materials. More recently it is being implemented to investigate the mechanical properties of pharmaceutical crystals. Integration of correlative microscopy techniques and environmental control opened the door for advanced structure-property correlation under processing conditions. Preventing the degradation of active pharmaceutical ingredients from external factors such as humidity, temperature, or pressure is important during processing. This review deals with the recent developments in the synchronized nanomechanical measurements of pharmaceutical crystals toward the fast and effective development of high-quality pharmaceutical drug products. This review also summarizes some recent reports to intensify how one can design and control the nanomechanical properties of pharmaceutical solids. Measurement challenges and the scope for studying nanomechanical properties of pharmaceutical crystals using nanoindentation as a function of crystal structure and in turn to develop fundamental knowledge in the structure-property relationship with the implications for drug manufacturing and development are discussed in this review. This review further highlights recently developed capabilities in nanoindentation, for example, variable temperature nanoindentation testing, in situ imaging of the indented volume, and nanoindentation coupled Raman spectroscopy that can offer new quantitative details on nanomechanical behavior of crystals and will play a decisive role in the development of coherent theories for nanomechanical study of pharmaceutical crystal.

A novel soluble lornoxicam-sodium chelate monohydrate with improved plasticity and tabletability

Lornoxicam (LOR), a BCS Ⅱ nonsteroidal anti-inflammatory drug, has been clinically utilized for moderate to severe acute pain management. However, it has poor water solubility and insufficient tabletability, leading to erratic absorption and challenge in tablet processability. This study reported a novel solid state of LOR (i.e., LOR sodium chelate monohydrate, LOR-Na·H₂O) with significantly improved solubility, dissolution rate and tabletability. The prepared chelate (CCDC No.: 2125157) contains LOR^-, Na⁺, and H₂O in a molar ratio of 1:1:1, where Na⁺ ions bridged with O(5) of amide group, and N(2) of pyridine group on LOR^-, as well as O(4) on H₂O through coordination bonds. LOR-Na·H₂O displayed a superior dissolution rate (5∼465 folds) than commercial LOR due to its increased wettability (contact angle: 74.5° vs 85.6°) and lower solvation free energy (∼2-fold). In addition, the significant improvement in tabletability was caused by high plasticity and deformability, which was attributed to its special interlayer gliding with weak bonding interactions across layers but strong coordination bonding interactions within layers. The novel LOR-Na·H₂O with significantly enhanced pharmaceutical performance offers a promising strategy for further product development.

Indomethacin Polymorph δ Revealed To Be Two Plastically Bendable Crystal Forms by 3D Electron Diffraction: Correcting a 47-Year-Old Misunderstanding

Indomethacin is a clinically classical non-steroidal anti-inflammatory drug that has been marketed since 1965. The third polymorph, Form δ, was discovered by both melt and solution crystallization in 1974. δ-indomethacin cannot be cultivated as large single crystals suitable for X-ray crystallography and, therefore, its crystal structure has not yet been determined. Here, we report the structure elucidation of δ-indomethacin by 3D electron diffraction and reveal the truth that melt-crystallized and solution-crystallized δ-indomethacin are in fact two polymorphs with different crystal structures. We propose to keep the solution-crystallized polymorph as Form δ and name the melt-crystallized polymorph as Form θ. Intriguingly, both structures display plastic flexibility based on a slippage mechanism, making indomethacin the first drug to have two plastic polymorphs. This discovery and correction of a 47-year-old misunderstanding signify that 3D electron diffraction has become a powerful tool for polymorphic structural studies.

Recent advances in drug polymorphs: Aspects of pharmaceutical properties and selective crystallization

Drug polymorphism, an established term used to describe the phenomenon that a drug can exist in different crystalline phases, has attracted great interests in pharmaceutical field in consideration of its important role in affecting the pharmaceutical performance of oral formulations. This paper presents an overview of recent advances in the research on polymorphic drug systems including understandings on nucleation, crystal growth, dissolution, mechanical properties, polymorphic transformation, etc. Moreover, new strategies and mechanisms in the control of polymorphic forms are also highlighted in this review. Furthermore, challenges and trends in the development of polymorphic drugs are briefly discussed, aiming at developing effective and efficient pharmaceutical formulations containing the polymorphic drugs.

Puerarin-Na Chelate Hydrate Simultaneously Improves Dissolution and Mechanical Behavior

Puerarin monohydrate (PUEM), as the commercial solid form of the natural anti-hypertension drug puerarin (PUE), has low solubility, poor flowability, and mechanical properties. In this study, a novel solid form as PUE-Na chelate hydrate was prepared by a reactive crystallization method. Crystal structure analysis demonstrated that PUE-Na contains PUE^-, Na⁺, and water in a molar ratio of 1:1:7. It crystallizes in the monoclinic space group P2₁, and Na⁺ is linked with PUE^- and four water molecules through Na⁺ ← O coordination bonds. Another three crystal water molecules occupy channels along the crystallographic b-axis. Observing along the b-axis, the crystal structure features a distinct tubular helix and a DNA-like twisted helix. The complexation between Na⁺ and PUE^- in aqueous solution was confirmed by the Na⁺ selective electrode, indicating that PUE-Na chelate hydrate belongs to a type of chelate rather than organic metal salt. Compared with PUEM, PUE-Na exhibited a superior dissolution rate (i.e., ∼38-fold increase in water) owing to its lower solvation free energy and clear-enriched exposed polar groups. Moreover, PUE-Na enhanced the tabletability and flowability of PUEM, attributing to its better elastoplastic deformation and lower-friction crystal habit. The unique PUE-Na chelate hydrate with significantly enhanced pharmaceutical properties is a very promising candidate for future product development of PUE.

How can single particle compression and nanoindentation contribute to the understanding of pharmaceutical powder compression?

The deformation behaviour of a powder and, thus, of the individual particles is a crucial parameter in powder compaction and affects powder compressibility and compactibility. The classical approach for the characterization of the deformation behaviour is the performance of powder compression experiments combined with the application of mathematical models, such as the Heckel-Model, for the derivation of characteristic compression parameters. However, the correlation of these parameters with the deformation behaviour is physically often not well understood. Single particle compression and nanoindentation enables the in-depth investigation of the deformation behaviour of particulate materials. In this study, single particle compression experiments were performed for the characterization of the deformation behaviour of common pharmaceutical excipients and active pharmaceutical ingredients (APIs) with various, irregular particle morphologies of industrial relevance and the findings are compared with the results from powder compression. The technique was found useful for the characterization and clarification of the qualitative deformation behaviour. However, the derivation of a quantitative functional relationship between single particle deformation behavior and powder compression is limited. Nanoindentation was performed as complementary technique for the characterization of the micromechanical behavior of the APIs. A linear relationship between median indentation hardness and material densification strength as characteristic parameter derived by in-die powder compression analysis is found.

Functionality evaluation of co-processed excipients as diluents in tablets manufactured by wet granulation

Diluents are essential components of a tablet formulation. The type of diluent used in a formulation influences the quality of tablets produced from that formulation. The aim of this study was to evaluate the tableting properties of co-processed excipients (C-PEs) incorporated as diluents in tablet formulation by wet granulation. Metronidazole tablets were prepared by wet granulation incorporating different diluents that were either single component excipients (SCEs) (lactose and microcrystalline cellulose) or C-PEs (Ludipress®, StarLac®, Prosolv® and AVICEL®HFE). The granules obtained for each formulation were evaluated for particle size analysis, flow properties and compression properties. Tablets weighing 500 mg were compressed from the metronidazole granules on a Single Station Tablet Press using a 12 mm punch and die tooling system. The tablets were kept for 24 h post-production, and the properties of weight uniformity, thickness, tensile strength, friability, disintegration time and dissolution profile evaluated subsequently. Results of granule properties showed that variations in parameters evaluated was as a result of differences in the type and composition of diluent used in formulation. Compactibility and tabletability profile of metronidazole granules revealed a better performance with granules processed with C-PE based diluents compared to SCE-based diluents. Tablets formulated with C-PEs as diluents were uniform in tablet weight, disintegrated faster and yielded a faster drug release compared to tablet formulations containing SCEs as diluent. This study reveals the performance advantage of C-PEs as diluents in tablets manufactured by wet granulation and highlights the importance of rational selection of excipients during tablet formulation.

Pharmaceutical salt and salt hydrates of vortioxetine with sulfonic acid to ameliorate the solubility and hygroscopicity via the charge-assisted hydrogen bond assembly

Salt forms of vortioxetine (VOT) with three sulfonic acids have been designed and prepared in 1 : 1 stoichiometry ratio, and their crystal structures and physicochemical properties have also been characterized in detail.

Structure–property correlations in piracetam polytypes

Analysis of piracetam polytypes using energy-vector models, thermal expansion and nanoindentation measurements, produces a plausible link between their crystal structures and tableting behaviour.

Impact of polymorphism on mechanical properties of molecular crystals: a study of p-amino and p-nitro benzoic acid with nanoindentation

We report on nanoindentation data for two pairs of polymorphic compounds of p-aminobenzoic acid (pABA) and p-nitrobenzoic acid (pNBA) and compare it with existing data in the literature. We also explore on a new parameter, s-PBC, as a tool to estimate hardness.

Nanoindentation of Molecular Crystals: Lessons Learned from Aspirin

Nanoindentation enables the measurement of mechanical properties from single crystals with dimensions of a few micrometers. This experimental technique, however, has only recently been applied to molecular crystals. Key differences between the application of this technique to molecular crystals and metals and other inorganics are identified. From this, protocols for the measurement of hardness and elastic modulus of molecular crystals of pharmaceutical interest are proposed. Using form I aspirin as a model system, the impact of single crystal sample surface preparation (washing and cleaving) on the surface roughness is explored. We show the importance of using a calibration sample with hardness and stiffness close to that of molecular crystals for the acquisition of more accurate data. The issue of solvent occlusions formed during crystal growth is discussed as a source of material property variation as well as tip contamination. It is proposed that this in part explains the significantly larger variation of the measured mechanical properties among different single crystals compared to those performed on a unique sample. Because both the indentation modulus and the hardness can vary significantly for low depth indents, samples were tested over a wide range of depths, which revealed that a minimum depth of penetration is required for the acquisition of data. This experiment is crucial and needs to be carried out for every system under study since it allows for the determination of the minimum-working load. Post-indentation imaging combined with crystallographic analysis and molecular simulations allows for the characterization and rationalization of the material plastic deformation mechanisms.

Febuxostat ethanol monosolvate

The title compound, 2-(3-cyano-4-iso-but-oxyphen-yl)-4-methyl-1,3-thia-zole-5-car-b-oxy-lic acid ethanol monosolvate, C16H16N2O3S·C2H6O, (I), displays inter-molecular O-H⋯O and O-H⋯N bonds in which the carboxyl group of the febuxostat mol-ecule and the hydroxyl group of the ethanol mol-ecule serve as hydrogen-bond donor sites. These inter-actions result in a helical hydrogen-bonded chain structure. The title structure is isostructural with a previously reported methanol analogue.

A novel approach to design febuxostat-salicylic acid eutectic system: evaluation and characterization

The current study was aimed at investigating the febuxostat-salicylic acid (FXT-SAA) eutectic system using two polymorphs of FXT, form Q and form A.

Revealing the Role of Structural Features in Bulk Mechanical Performance of Ternary Molecular Solids of Isoniazid

Mechanical performance in ternary (3n) molecular solids has been rarely studied, and hence it is an interesting topic of investigation in the direct compression method of tableting. The structural features of 3n-eutectic (3n-Eu: INZ-ADP-NIC) and 3n-cocrystal (3n-Co: INZ:SUC:NIC) were explored to understand the bonding area-bonding strength (BA-BS) interplay. Higher compressibility and lower values of the Heckel parameter of 3n-Co as compared to 3n-Eu suggested its better deformation behavior, with BA being the predominant factor. The higher tensile strength and Walker analysis indicated a higher compressibility coefficient ( W) and lower pressing modulus ( L) for 3n-Eu, which was consistent with its better tabletability over 3n-Co. The higher compressibility and plastic energy, and higher value of L of 3n-Co, were attributed to the facile propagation (⟨-1' 0' 5'⟩) of the shearing molecular slip (-1 0 5) when subjected to the external mechanical stress. Thus, the overall higher tableting performance of 3n-Eu over 3n-Co was found due to the predominant BS and limited contribution of BA. The latter was the dominant factor in 3n-Co. Cohesive interactions, like the 3D mechanically interlocked structure of conglomerates of 3n-Eu, contributed toward the higher BS. Moreover, the prediction of better tabletability solely based on crystallographic feature slip planes (0D/1D/2D H-bonded layer (h k l) ⊥ vdW interactions) is warranted in pharmaceutical molecular solids. Eutectics with varying microstructural variants ( nL_α + nL_β + nL_γ) may open up the opportunity to manipulate the physicomechanical performance.

Molecular Understanding and Implication of Structural Integrity in the Deformation Behavior of Binary Drug-Drug Eutectic Systems

In eutectic, a lamellar microstructure offers better tableting than that of the nonreacted physical mixture. However, bulk deformation remains elusive in two binary eutectics. We hypothesized that the binary eutectic of a drug with different components, having different H-bonding dimensionalities and crystal structure, shall allow the understanding of the structural integrity in the bulk deformation behavior. The shearing molecular solid (FXT Q) shared a common composition with the viscoelastic crystal (ASP I) and brittle (PCM I), forming EM-1 (ϕ₁ = 41.27:58.73% w/w) and EM-2 (ϕ₂ = 41.10:58.90% w/w), respectively. The excess thermodynamic functions were contributed by high energy microstructures (nonbonding interactions) along incoherent phase boundaries (visualized under CLSM). The energy dispersive analysis enabled the recognition of the relative distribution of higher atoms over the heterogeneous surface. EM-1 (FXT Q-ASP I) demonstrated higher compressibility, tensile strength, and compactibility (CTC profile) compared to those of EM-2 (FXT Q-PCM I) over a range of applied compaction pressures. The lower true yield strength (σ_0(EM-1) = 138.66 MPa) of EM-1 as compared to that of EM-2 (σ_0(EM-2) = 166.66 MPa) suggested a better deformation performance and incipient plasticity quantified from the "out-of-die" Heckel analysis. From Ryshkewitch analysis, the tensile strength at zero porosity (τ₀₁ = 3.83 MPa) was predicted to be higher for EM-1 than EM-2 (τ₀₂ = 2.54 MPa). The higher bonding strength of EM-1 was contributed to the additional influence of true density and isotropic van der Waals interactions of ASP I (0D). In contrast, EM-2 demonstrated lower compressibility and compactibility, having herringbone molecular packing of PCM I (1D) with a common shearing component (FXT Q (1D)). This study confirmed that the intrinsic deformational and chemical nature of the second component defined the compressibility and compactibility tendency to a greater extent in the tableting performance of conglomerates of crystalline solid solution.

Development and Optimization of a Starch-Based Co-processed Excipient for Direct Compression Using Mixture Design

The development of novel excipients with enhanced functionality has been explored using particle engineering by co-processing. The aim of this study was to improve the functionality of tapioca starch (TS) for direct compression by co-processing with gelatin (GEL) and colloidal silicon dioxide (CSD) in optimized proportions. Design of Experiment (DoE) was employed to optimize the composition of the co-processed excipient using the desirability function and other supporting studies as a basis for selecting the optimized formulation. The co-processed excipient (SGS) was thereafter developed by the method of co-fusion. Flow and compaction studies of SGS were carried out in comparison to its parent component (TS) and physical mixture (SGS-PM). Tablets were prepared by direct compression (DC) containing ibuprofen (200 mg) as a model for poor compressibility using SGS, Prosolv®, and StarLac® as multifunctional excipients. The optimized composition of SGS corresponded to TS (90%), GEL (7.5%), and CSD (2.5%). The functionality of SGS was improved relative to SGS-PM in terms of flow and compression. Tablets produced with SGS were satisfactory and conformed to USP specifications for acceptable tablets. SGS performed better than Prosolv® in terms of disintegration and was superior to StarLac with respect to tensile strength and disintegration time. The application of DoE was successful in optimizing and developing a starch-based co-processed excipient that can be considered for direct compression tableting.

Curcumin: pharmaceutical solids as a platform to improve solubility and bioavailability

The remarkable improvements in the pharmacokinetics and high bioavailability of curcumin polymorphs, amorphous, cocrystals, eutectics, and coamorphous solids are discussed. The importance of pharmaceutical solids in the advanced formulation development of herbal and bioactive molecule curcumin is presented.

Crystal and Particle Engineering Strategies for Improving Powder Compression and Flow Properties to Enable Continuous Tablet Manufacturing by Direct Compression

Continuous manufacturing of tablets has many advantages, including batch size flexibility, demand-adaptive scale up or scale down, consistent product quality, small operational foot print, and increased manufacturing efficiency. Simplicity makes direct compression the most suitable process for continuous tablet manufacturing. However, deficiencies in powder flow and compression of active pharmaceutical ingredients (APIs) limit the range of drug loading that can routinely be considered for direct compression. For the widespread adoption of continuous direct compression, effective API engineering strategies to address power flow and compression problems are needed. Appropriate implementation of these strategies would facilitate the design of high-quality robust drug products, as stipulated by the Quality-by-Design framework. Here, several crystal and particle engineering strategies for improving powder flow and compression properties are summarized. The focus is on the underlying materials science, which is the foundation for effective API engineering to enable successful continuous manufacturing by the direct compression process.