Indomethacin-saccharin cocrystal: design, synthesis and preliminary pharmaceutical characterization

Co-crystal of tramadol-celecoxib (CTC) for acute moderate-to-severe pain

OBJECTIVE

This narrative review aims to provide a clinical perspective on the potential role of co-crystal of tramadol-celecoxib (CTC) in the management of acute moderate-to-severe pain by synthesizing the available preclinical and clinical data, with emphasis on phase 3 trials.

METHODS

A non-systematic literature review was performed using a targeted PubMed search for articles published between January 1, 2000, and May 2, 2023; all publication types were permitted, and selected articles were limited to those published in English. Search results were manually reviewed to identify references based on their preclinical and clinical relevance to CTC and management of acute moderate-to-severe pain.

RESULTS

The crystalline structure of CTC alters the physicochemical properties of tramadol and celecoxib, modifying their pharmacokinetics. If taken in a free combination, tramadol reduces absorption of celecoxib. Conversely, administration of CTC slows tramadol absorption and lowers its maximum plasma concentration, while increasing celecoxib plasma concentration through its enhanced release. In clinical studies across models of acute moderate-to-severe pain, CTC demonstrated an early onset of analgesia, with improved efficacy and lower rescue medication use, compared with either agent alone. CTC's safety profile was in line with that expected for the individual components; no additive effects were observed. CTC exhibited tramadol-sparing effects, with efficacy seen at lower daily/cumulative opioid doses vs. tramadol alone.

CONCLUSIONS

Results from phase 3 trials suggest that the modified physicochemical properties of tramadol and celecoxib in CTC translate into an improved clinical benefit-risk profile, including fewer opioid-related adverse effects due to lower overall opioid dosing.

Drug-Coformer Loaded-Mesoporous Silica Nanoparticles: A Review of the Preparation, Characterization, and Mechanism of Drug Release

Drug-coformer systems, such as coamorphous and cocrystal, are gaining recognition as highly effective strategies for enhancing the stability, solubility, and dissolution of drugs. These systems depend on the interactions between drug and coformer to prevent the conversion of amorphous drugs into the crystalline form and improve the solubility. Furthermore, mesoporous silica (MPS) is also a promising carrier commonly used for stabilization, leading to solubility improvement of poorly water-soluble drugs. The surface interaction of drug-MPS and the nanoconfinement effect prevent amorphous drugs from crystallizing. A novel method has been developed recently, which entails the loading of drug-coformer into MPS to improve the solubility, dissolution, and physical stability of the amorphous drug. This method uses the synergistic effects of drug-coformer interactions and the nanoconfinement effect within MPS. Several studies have reported successful incorporation of drug-coformer into MPS, indicating the potential for significant improvement in dissolution characteristics and physical stability of the drug. Therefore, this study aimed to discuss the preparation and characterization of drug-coformer within MPS, particularly the interaction in the nanoconfinement, as well as the impact on drug release and physical stability.

Illuminating milling mechanochemistry by tandem real-time fluorescence emission and Raman spectroscopy monitoring

In pursuit of accessible and interpretable methods for direct and real-time observation of mechanochemical reactions, we demonstrate a tandem spectroscopic method for monitoring of ball-milling transformations combining fluorescence emission and Raman spectroscopy, accompanied by high-level molecular and periodic density-functional theory (DFT) calculations, including periodic time-dependent (TD-DFT) modelling of solid-state fluorescence spectra. This proof-of-principle report presents this readily accessible dual-spectroscopy technique as capable of observing changes to the supramolecular structure of the model pharmaceutical system indometacin during mechanochemical polymorph transformation and cocrystallisation. The observed time-resolved in situ spectroscopic and kinetic data are supported by ex situ X-ray diffraction and solid-state nuclear magnetic resonance spectroscopy measurements. The application of first principles (ab initio) calculations enabled the elucidation of how changes in crystalline environment, that result from mechanochemical reactions, affect vibrational and electronic excited states of molecules. The herein explored interpretation of both real-time and ex situ spectroscopic data through ab initio calculations provides an entry into developing a detailed mechanistic understanding of mechanochemical milling processes and highlights the challenges of using real-time spectroscopy.

Recent Advances in Co-Former Screening and Formation Prediction of Multicomponent Solid Forms of Low Molecular Weight Drugs

Multicomponent solid forms of low molecular weight drugs, such as co-crystals, salts, and co-amorphous systems, are a result of the combination of an active pharmaceutical ingredient (API) with a pharmaceutically acceptable co-former. These solid forms can enhance the physicochemical and pharmacokinetic properties of APIs, making them increasingly interesting and important in recent decades. Nevertheless, predicting the formation of API multicomponent solid forms in the early stages of formulation development can be challenging, as it often requires significant time and resources. To address this, empirical and computational methods have been developed to help screen for potential co-formers more efficiently and accurately, thus reducing the number of laboratory experiments needed. This review provides a comprehensive overview of current screening and prediction methods for the formation of API multicomponent solid forms, covering both crystalline states (co-crystals and salts) and amorphous forms (co-amorphous). Furthermore, it discusses recent advances and emerging trends in prediction methods, with a particular focus on artificial intelligence.

An Intragastric Delivery Device Employing FDM Technology: 3D-Printed Tablet Containing Green Developed Mosapride-Saccharin Co-crystals

Mosapride citrate (MC) is a poorly soluble short half-life drug with more pronounced absorption in the stomach. The present study aimed to incorporate MC co-crystals with enhanced solubility into 3D-printed floating tablets. MC co-crystals were prepared via the green method using Saccharin sod. as a co-former at a (1:1) molar ratio. The prepared co-crystals were assessed for solubility, FTIR, thermal behavior, and SEM. Then, it was incorporated into zero % infill 3D-printed tablets of different configurations at two thickness levels by the FDM printing technique. Printed tablets were evaluated for dimensions, weight deviation, friability, and in vitro floating behavior. Drug release and kinetic of the MC release were also assessed. Solubility study of the co-crystals showed a significant (p value < 0.05) increased solubility over pure MC. FTIR and thermal behavior confirmed hydrogen bonding formation during co-crystallization. The obstructed particles had an erratic protrusion form, similar to a nodule, as illustrated by SEM. The printed tablets showed acceptable physicochemical properties. Tablets floated for about ≥ 12 h without floating lag time. In vitro drug release exhibited variable extended release profiles with different lag times depending on the configuration indicating that the tablet's wall thickness and surface area were the factors manipulated to control drug release. Kinetic analysis of the release data displayed intermediate kinetics between zero-order and diffusional kinetics. The intragastric extended release profile for MC co-crystals of improved solubility could be successfully, economically, and quickly developed utilizing the 3D printing technique.

Co-Crystallization Approach to Enhance the Stability of Moisture-Sensitive Drugs

Stability is an essential quality attribute of any pharmaceutical formulation. Poor stability can change the color and physical appearance of a drug, directly impacting the patient's perception. Unstable drug products may also face loss of active pharmaceutical ingredients (APIs) and degradation, making the medicine ineffective and toxic. Moisture content is known to be the leading cause of the degradation of nearly 50% of medicinal products, leading to impurities in solid dose formulations. The polarity of the atoms in an API and the surface chemistry of API particles majorly influence the affinity towards water molecules. Moisture induces chemical reactions, including free water that has also been identified as an important factor in determining drug product stability. Among the various approaches, crystal engineering and specifically co-crystals, have a proven ability to increase the stability of moisture-sensitive APIs. Other approaches, such as changing the salt form, can lead to solubility issues, thus making the co-crystal approach more suited to enhancing hygroscopic stability. There are many reported studies where co-crystals have exhibited reduced hygroscopicity compared to pure API, thereby improving the product's stability. In this review, the authors focus on recent updates and trends in these studies related to improving the hygroscopic stability of compounds, discuss the reasons behind the enhanced stability, and briefly discuss the screening of co-formers for moisture-sensitive drugs.

Sulfonic Acid Derivatives in the Production of Stable Co-Amorphous Systems for Solubility Enhancement

Co-amorphization is a promising approach to stabilize drugs in the amorphous form. Olanzapine, a poorly water-soluble drug was used in this study. Sulfonic acids (saccharin, cyclamic acid and acesulfame), free and in salt forms, were used as co-formers and compared with carboxylic acids commonly used in the preparation of co-amorphous systems. Several manufacturing techniques were tested, and the co-amorphous systems characterized by differential scanning calorimetry, X-ray powder diffraction, thermogravimetry and Fourier-transform infrared spectroscopy. Free sulfonic acids produced co-amorphous systems with the drug, unlike their salts. Spectroscopy data suggests the formation of salts between olanzapine and the sulfonic acids, used as co-formers. The co-amorphous system produced with saccharin by solvent evaporation, showed the most notable solubility enhancement (145 times). The stability of amorphous and co-amorphous olanzapine systems was assessed upon exposure to stress conditions during storage. Amorphized olanzapine readily reconverted back to the crystalline form while sulfonic acids:olanzapine co-amorphous were stable for up to 24 weeks in low/medium humidity conditions (11-75% RH). Results highlight the potential advantages offered by sulfonic acids as co-formers to produce stable and more soluble co-amorphous olanzapine.

In Situ Co-Amorphization of Olanzapine in the Matrix and on the Coat of Pellets

In situ amorphization is a promising approach, considered in the present work, to enhance the solubility and dissolution rate of olanzapine, while minimizing the exposure of the amorphous material to the stress conditions applied during conventional processing. The production of pellets by extrusion/spheronization and the coating of inert beads were investigated as novel methods to promote the co-amorphization of olanzapine, a poorly water-soluble drug, and saccharin. Samples were characterized using differential scanning calorimetry, X-ray powder diffraction, Fourier-transform infrared spectroscopy and scanning electron microscopy, and dissolution and stability testing. The co-amorphous produced were compared with crystalline olanzapine, or physical mixture of olanzapine and saccharin. Results suggested that the addition of water to mixtures containing olanzapine and saccharin during the production of pellets, and the coating of inert beads, induced the in situ co-amorphization of these substances. The coating of inert beads enhanced the solubility and dissolution rate of olanzapine, especially when compared to pellets coated with the crystalline drug, but also with pellets containing the co-amorphous entity in the matrix of beads. Nine months stability tests (23 °C/60% RH) confirmed the preservation of the solid-state properties of the co-amorphous form on/in pellets. Overall, results highlighted the feasibility and benefits of in situ co-amorphization, either when the drug was entrapped in the pellets matrix, or preferentially applied directly on the surface of pellets.

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.

Gelation switch of polyamorphic indomethacin depending on the thermal procedure

Amorphous indomethacin (IMC) prepared under different thermal procedures via melt quenching method showed significantly different dissolution behaviors. This study aims to investigate the influence of thermal procedures on the formation of IMC polyamorphism and to explore the mechanism for their different dissolution behaviors. Amorphous IMC samples were prepared by melting crystalline IMC under a series of temperatures (160-195 °C), respectively, followed by quenching in liquid nitrogen. Samples obtained under 170 °C exhibited bi-halo shapes at ∼15° and ∼26° (2θ), while the ones above 175 °C showed a single halo at ∼21° (2θ), suggesting amorphous IMC prepared under different thermal procedures probably have different local molecular arrangements. In comparison to crystalline IMC, amorphous IMC obtained under 170 °C showed significantly higher dissolution profiles with good dispersibility in aqueous medium, however, all amorphous IMC samples prepared above 175 °C demonstrated much lower dissolution with significant gelation, which seemed like a gelation switch existed for polyamorphic IMC when the preparation temperature was between 170 and 175 °C. Based on physicochemical characterizations, amorphous IMC prepared under 170 °C had higher surface free energy, more surficial hydrophilic groups and better wettability than the ones made above 175 °C. Molecular dynamics simulations revealed that the amorphous samples prepared below 170 °C had similar binding energy values in the range of 310.045-325.479 kcal/mol, while those prepared above 175 °C were significantly lower within 212.193-235.073 kcal/mol. Such binding energy difference might be responsible for their different local molecular arrangements after different thermal procedures. The current study deeply reminds us that the thermal procedure of preparation methods may significantly affect the physicochemical properties of amorphous materials, which should be paid special attention to the polymorphic selection during pharmaceutical development.

Levofloxacin Cocrystal/Salt with Phthalimide and Caffeic Acid as Promising Solid-State Approach to Improve Antimicrobial Efficiency

To overcome the issue of multidrug resistant (MDR) microbes, the exploration of ways to improve the antimicrobial efficiency of existing antibiotics is one of the promising approaches. In search of synthons with higher efficiency, in current investigations, cocrystal and amorphous salt of levofloxacin hemihydrate (LEV) were developed with phthalimide (PTH) and caffeic acid (CFA). New materials were characterized with the help of FT-IR, Raman spectroscopy, powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Shifting, attenuation, appearance/disappearance and broadening of bands were observed in the FT-IR and Raman spectra of the materials as evidence of the required product. The PXRD diffraction pattern observed for LEV-PTH indicated cocrystal while halo diffractogram of LEV-CFA revealed amorphous nature. DSC/TG analysis confirmed the hydrated nature of the cocrystal/salt. The dissolution rate and antimicrobial activity against selected strains, K.pneumonia, E. coli and S. typhi of parent drug and the new material were compared. The zone of inhibition (ZI) observed for 5 µg LEV-PTH was 30.4 + 0.36 (K. pneumonia), 26.33 + 0.35 (E. coli) and 30.03 + 0.25 mm (S. typhi) while LEV-CFA salt (5 µg) against the same strains inhibited 33.96 ± 0.25, 31.66 ± 0.35 and 27.93 ± 0.40 mm, respectively. These novel formulations enhance the dissolution rate as well as antibacterial efficiency and are expected to be potent against MDR bacterial strains.

Combination of co-crystal and nanocrystal techniques to improve the solubility and dissolution rate of poorly soluble drugs

Purpose

Solubility and dissolution rate are essential for the oral absorption and bioavailability of poorly soluble drugs. The aim of this study was to prepare nano-co-crystals by combination of nanocrystal and co-crystal technologies, and investigate its effect, in situ, on increased kinetic solubility and dissolution rate.

Methods

Co-crystals of itraconazole-fumaric acid, itraconazole-succinic acid, indomethacin-saccharin and indomethacin-nicotinamide were prepared and nano-sized by wet milling. The particle size and solid state of the co-crystals were characterized by optical microscope, LD, PCS, DSC and XRPD before and after milling.

Results

300-450 nm sized nano-co-crystals with a stable physical solid state were successfully prepared. Nano-co-crystals exhibited a lower crystallinity reduction than nanocrystals after wet milling. The particle size effect on the kinetic solubility of co-crystals was analysed for macro-, micro- and nano-co-crystals with in situ kinetic solubility studies. The maximum kinetic solubility of nano-co-crystals increased with excess conditions until a plateau. The highest increase was obtained with itraconazole-succinic acid nano-co-crystals with a kinetic solubility of 263.5 ± 3.9 μg/mL which was 51.5 and 6.6 times higher than the solubility of raw itraconazole and itraconazole-succinic acid co-crystal.

Conclusions

The synergistic effect of nanocrystals and co-crystals with regard to increased kinetic solubility and dissolution rate was proven. The combination of the advantages of nanocrystals and co-crystals is a promising formulation strategy to increase both the solubility and dissolution rate of poorly soluble drugs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11095-022-03243-9.

Improved Pharmaceutical Properties of Ritonavir through Co-crystallization Approach with Liquid Assisted Grinding Method

Ritonavir is a BCS class II antiretroviral agent which shows poor aqueous solubility and low oral bioavailability. The cocrystallization approach was selected to overcome these problems and to improve the physicochemical and mechanical properties of Ritonavir. The novel pharmaceutical Ritonavir-L-tyrosine cocrystals (RTC at a molar ratio of 1:1) were synthesized using the liquid assisted grinding (LAG) method. The possibility of molecular interactions between drug and coformer were studied using Gold software version 5.2. The newly formed crystalline solid phase was characterized through Differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), Fourier transform-infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), and Solid-State Nuclear magnetic resonance (SSNMR). The improved pharmaceutical properties were confirmed by solubility, dissolution, and powder compaction study. The prepared cocrystals exhibited an 11.24-fold increase in solubility and a 3.73-fold increase in % of drug release at 1 h compared to pure drug. Tabletability and compaction behaviour of the pure drug and cocrystal with added excipients assessed. The tabletability profile of cocrystals showed enhanced tabletting performance as compared to pure drug. The stability studies revealed that cocrystals were stable for at least one month when stored at 40 °C/75% RH and 25 °C/60% RH conditions. The cocrystallization approach was found to be very promising and showed an overall improved performance of Ritonavir.

Profoundly improved photostability of dimetronidazole by cocrystallization

Cocrystallization with saccharine (SAC) significantly improved photostability of dimetronidazole (DMZ), an veterinary antibiotic.

Molecular interactions of indomethacin and amino acids: Computational approach

Molecular interactions of indomethacin (IND) and amino acids (AA) were investigated in this work by employing the computational approaches. To this aim, the models of IND-AA were stabilized by performing density functional theory (DFT) calculations yielding the most favorable configurations regarding the energy values. Next, the approach of quantum theory of atoms in molecules (QTAIM) was used to recognize the roles of interactions and their significance in the bimolecular models. The results of interaction energies indicate that tryptophan (TRP) and phenylalanine (PHE) could be considered for participating in strong interactions with the IND substance. The results of QTAIM indicated that not only the electronegative atomic centers, but also homo-atomic centers could play significant roles in formations of IND-AA bimolecular models.

Structure determination, thermal stability and dissolution rate of δ-indomethacin

The structure solution of the δ-polymorph of indomethacin was obtained using three-dimensional electron diffraction. This form shows a significantly enhanced dissolution rate compared with the more common and better studied α- and γ-polymorphs, indicating better biopharmaceutical properties for medicinal applications. The structure was solved in non-centrosymmetric space group P2₁ and comprises two molecules in the asymmetric unit. Packing and molecule conformation closely resemble indomethacin methyl ester and indomethacin methanol solvate. Knowledge of the structure allowed the rational interpretation of spectroscopic IR and Raman data for δ-polymorph and a tentative interpretation for still unsolved indomethacin polymorphs. Finally, we observed a solid-solid transition from δ-polymorph to α-polymorph that can be driven by similarities in molecular conformation.

New Cocrystals of Antipsychotic Drug Aripiprazole: Decreasing the Dissolution through Cocrystallization

Cocrystallization is an important route to tuning the solubility in drugs development, including improving and reducing. Five cocrystals of aripiprazole (ARI) with resveratrol (RSV) and kaempferol (KAE), ARI-RSV, ARI₂-RSV₁·MeOH, ARI-KAE, ARI-KAE·EtOH, ARI-KAE·IPA, were synthesized and characterized. The single crystal of ARI₂-RSV₁·MeOH, ARI-KAE·EtOH, and ARI-KAE·IPA were analyzed by single crystal X-ray diffraction (SCXRD). The SCXRD showed multiple intermolecular interactions between API and the coformers, including hydrogen bond, halogen bond, and π-π interactions. Dissolution rate of the two nonsolvate ARI-RSV and ARI-KAE cocrystals were investigated through powder dissolution experiment in pH = 4.0 acetate buffer and pH = 6.8 phosphate buffer. The result showed that RSV could reduce the dissolution rate and solubility of ARI in both medium through cocrystallization. However, KAE improved the dissolution rate and solubility of ARI in pH = 4.0 medium, on the contrary, the two solubility indicators of ARI were both reduced for ARI-KAE cocrystal.

Effect of drug-coformer interactions on drug dissolution from a coamorphous in mesoporous silica

In this study, the molecular state of ritonavir (RTN)-saccharin (SAC) coamorphous incorporated into mesoporous silica by solvent evaporation and the effect of SAC on the RTN dissolution from mesopores were investigated. The amorphization of RTN-SAC was confirmed as a halo pattern in powder X-ray diffraction measurements and a single glass transition event in the modulated differential scanning calorimetry (MDSC) curve. ¹³C solid-state NMR spectroscopy revealed a hydrogen bond between the thiazole nitrogen of RTN and the amine proton of SAC. The glass transition of the RTN-SAC coamorphous in mesoporous silica was not found in the MDSC curve, indicating that RTN and SAC were monomolecularly incorporated into the mesopores. Solid-state NMR measurements suggested that the co-incorporation of SAC into the mesopores decreased the local mobility of the thiazole group of RTN via hydrogen bond formation. The RTN-SAC 1:1 coamorphous in mesoporous silica retained the X-ray halo-patterns after 30 d of storage, even under high temperature and humidity conditions. In the dissolution test, the RTN-SAC 1:1 coamorphous in mesoporous silica maintained RTN supersaturation for a longer time than the RTN amorphous in mesoporous silica. This study demonstrated that the drug-coformer interaction within mesoporous silica can significantly improve drug dissolution.

Terahertz spectroscopic characterizations and DFT calculations of indomethacin cocrystals with nicotinamide and saccharin

Co-crystallization is an effective strategy to improve the drug properties such as solubility and stability. However, its thermodynamic backgrounds, especially lattice vibration, haven't been fully understood. In this work, indomethacin (IND) cocrystals formed with nicotinamide (NIC) and saccharin (SAC) are successfully characterized by using terahertz spectroscopy. DFT calculations at PBE-D3 level with and without constrained unit cell are performed to predict the absorption peaks at spectral range. The results suggest that the DFT calculations with constrained unit cell achieve a better agreement with experimental observations. Based on the optimized geometries and calculated phonons, the thermodynamic contributions from lattice vibrations to cocrystal formations are further evaluated. The findings reveal that the vibrational energy plays a comparable role with electronic energy, but has an opposite impact on these two cocrystal formations.

Cocrystal engineering of pharmaceutical solids: therapeutic potential and challenges

This highlight presents an overview of pharmaceutical cocrystal production and its potential in reviving problematic properties of drugs in different dosage forms. The challenges and future outlook of its translational development are discussed.

Synthesis and characterization of meloxicam eutectics with mandelic acid and saccharin for enhanced solubility

Meloxicam (MLX) is a non-steroidal anti-inflammatory which is practically insoluble in water, requiring high concentrations to reach therapeutic levels and causing frequently gastrointestinal effects. In this way, the aim of this study was to synthesize two eutectic mixtures of MLX with mandelic acid (MND) and saccharin (SAC) by liquid-assisted grinding resulting in a multicomponent material with enhanced solubility. Mixtures were studied in different stoichiometric and eutectic point was found for each eutectic by Binary phase diagram and Tamman's triangle, with 0.33 molar fraction of MLX for SAC and MND. Eutectics were characterized by thermoanalytical techniques (TG-DSC, EGA, DSC, and DSC microscopy), infrared spectroscopy, and X-ray powder diffraction. Thermal behavior was studied and videos of the materials being heated were available. A polymorphic transition was discovered and studied for MLX-MND eutectic. Each new system was evaluated by solubility, dissolution, and hygroscopicity tests. Eutectics showed an increase in solubility of 1.7× (MLX-MND1), 3.1× (MLX-MND2), and 1.3× (MLX-SAC) with slower dissolution profile when compared with MLX. All new solid forms showed high hygroscopicity at 98% relative humidity with 27.9 and 58.9% increase in mass at day four for MLX-SAC and MLX-MND, deliquescence occurs at day 6. The experiments and analysis in this study help to understand the behavior of eutectics and evaluate them as an approach to modify properties in drugs.

Benzodiazepines co-crystals screening using FTIR and Raman spectroscopy supported by differential scanning calorimetry

Co-crystals, which are defined as "solids that are crystalline materials composed of two or more molecules in the same crystal lattice" have recently been the focus of increased interest in the pharmaceutical industry since co-crystallization can improve unfavorable physicochemical properties of active pharmaceutical ingredients. Thus, the quest for new co-crystal screening methods has become an issue of importance. The aim of this work was, therefore, to show to what extent expanded methodology based on FTIR and Raman spectroscopy supported by the DSC method can be used as a reliable tool to screen co-crystallization. Because co-crystals of benzodiazepines had not yet been obtained, a set of 72 binary mixtures composed of eight 1,4-benzodiazepine derivatives and nine coformers were used as model substances. Potential co-crystals were prepared in solid-state by liquid-assisted grinding procedure. The characteristic FTIR and Raman bands which reflect hydrogen bond formation between benzodiazepine and coformer were used as proof of co-crystal creation. DSC was used as a supporting tool to reflect the phase transitions which occur during co-crystallization. As a result of the study, four potential co-crystals can be selected: lorazepam with nicotinamide, chlordiazepoxide with p-aminobenzoic and saccharin, and estazolam with fumaric acid. The detailed spectral and thermal characteristics of these systems are presented in this work. Thus, the proposed methodology of co-crystal screening based on FTIR and Raman data supported by the DSC examination of phase transitions facilitates the screening and detection of benzodiazepine co-crystal prepared by short time components ground with a slight additional volume of solvent.

Pharmaceutical Co-Crystallization: Regulatory Aspects, Design, Characterization, and Applications

Pharmaceutical co-crystals are novel class of pharmaceutical substances, which possess an apparent probability of advancement of polished physical properties offering stable and patentable solid forms. These multi-component crystalline forms influence pertinent physicochemical parameters like solubility, dissolution rate, chemical stability, physical stability, etc. which in turn result in the materials with superior properties to those of the free drug. Co-crystallization is a process by which the molecular interactions can be altered to optimize the drug properties. Co-crystals comprise a multicomponent system of active pharmaceutical ingredient (API) with a stoichiometric amount of a pharmaceutically acceptable coformer incorporated in the crystal lattice. By manufacturing pharmaceutical co-crystals, the physicochemical properties of a drug can be improved thus multicomponent crystalline materials have received renewed interest in the current scenario due to the easy administration in the pharmaceutical industry. There is an immense amount of literature available on co-crystals. However, there is a lack of an exhaustive review on a selection of coformers and regulations on co-crystals. The review has made an attempt to bridge this gap. The review also describes the methods used to prepare co-crystals with their characterization. Brief description on the pharmaceutical applications of co-crystals has also been incorporated here. Efforts are made to include reported works on co-crystals, which further help to understand the concept of co-crystals in depth.

Application of spray freeze drying to theophylline-oxalic acid cocrystal engineering for inhaled dry powder technology

Spray freeze drying (SFD) produces suitable particles for the pharmaceutical formulation of dry powders used in dry powder inhalers (DPIs). However, SFD particles have large specific surface area and are partially made up of amorphous solids; this state is hygroscopic and would lead to changes in physicochemical properties by humidity when the particles are stored over the long-term or under high humidity conditions such as in the lungs. This study focused on the application of SFD with a cocrystal technique which can add humidity resistance to the active pharmaceutical ingredients (APIs), and the investigation of the physicochemical properties under high humidity conditions. Cocrystal samples containing theophylline anhydrate (THA) and oxalic acid (OXA) in a molar ratio of 2:1 were prepared by SFD. The crystalline structure, thermal behavior, solid-state, hygroscopicity, stability, and aerodynamic properties were evaluated. Simultaneous in situ measurement by near-infrared and Raman (NIR-Raman) spectroscopy was performed to analyze the humidification process. The SFD sample had a porous particle and an optimal aerodynamic particle size (3.03 µm) although the geometric particle diameter was 7.20 µm. In addition, the sample formed the THAOXA cocrystal with partial coamorphous. The hydration capacity and pseudopolymorphic transformation rate of the SFD sample were much lower than those of THA under conditions of 96.4% relative humidity and 40.0°C temperature because of the cocrystal formation. The reasons were discussed based on the crystalline structure and energy. The SFD technology for cocrystallization would enable the pharmaceutical preparation of DPI products under environmentally friendly conditions.

The first zwitterionic cocrystal of indomethacin with amino acid showing optimized physicochemical properties as well as accelerated absorption and slowed elimination in vivo

The first zwitterionic cocrystal of indomethacin (INC) with proline (PL) with optimized in vitro/in vivo properties was prepared and characterized.

A 5-fluorouracil–kaempferol drug–drug cocrystal: a ternary phase diagram, characterization and property evaluation

A drug–drug cocrystal of 5-fluorouracil and kaempferol was comprehensively investigated and exhibits optimized solubility behavior in comparison with individual APIs.

Crystallisation parameters effect on the particle size distribution (PSD) of carbamazepine-saccharin (CBZ-SAC) co-crystals in batch cooling crystallisation

The crystallisation parameters effect on the particle size distribution (PSD) of carbamazepine-saccharin (CBZ-SAC) co-crystals in batch cooling crystallisation is presented. The particle size distribution study of CBZ-SAC co-crystals revealed that the multimodal with broad PSD was found for CBZ concentration of 19.14 mg/ml. Meanwhile, the unimodal with broad PSD were observed at CBZ concentration of 17.01 mg/ml and 17.96 mg/Crystal characterisation using differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), Fourier transform infrared (FTIR) and optical microscopy confirm the solid formed is CBZ-SAC co-crystal Form I with plate-like crystal morphology.

Formation of Indomethacin-Saccharin Cocrystals during Wet Granulation: Role of Polymeric Excipients

Formulation of a cocrystal into a solid pharmaceutical dosage form entails numerous processing steps during which there is risk of dissociation. In an effort to reduce the number of unit operations, we have attempted the in situ formation of an indomethacin-saccharin (INDSAC) cocrystal during high-shear wet granulation (HSWG). HSWG of IND (poorly water-soluble drug) and SAC (coformer), with polymers (granulating agents), was carried out using ethanol as the granulation liquid and yielded INDSAC cocrystal granules. Therefore, cocrystal formation and granulation were simultaneously accomplished. Our objectives were to (i) evaluate the influence of polymers on cocrystal formation kinetics during wet granulation and (ii) mechanistically understand the role of polymers in facilitating the cocrystal formation. Polyvinylpyrrolidone (PVP), hydroxypropyl cellulose (HPC), and polyethylene oxide (PEO) were chosen to investigate the influence of soluble polymers. The cocrystal formation kinetics was influenced by the polymer (PVP < HPC < PEO) and its concentration. The interaction of the polymer with cocrystal components inhibited the cocrystal formation. Complete cocrystal formation was observed in the presence of PEO, a polymer which does not interact with IND and SAC.

A New Method for Classification of Salts and Cocrystals Using Solid-State UV Spectrophotometry

Salt and cocrystal formulations are widely used as techniques to improve physicochemical properties of compounds. Some spectrometric techniques to distinguish cocrystals from salts have been reported; however, it has not been possible to adapt these formulations with many compounds, because of limitations, high difficulty, and exceptions. Therefore, we focused on the possibility of UV spectrometry, which had not been reported as a classification technique for salts and cocrystals. The integration values of solid-state UV/visible (Vis) spectra of indomethacin salts were larger than those of physical mixtures of indomethacin and counter molecules, while that of indomethacin cocrystal was not large compared with that of the physical mixture. From these results, differences between a salt and a cocrystal were observed in their solid-state UV/Vis absorption spectra for indomethacin complexes. Therefore, it is suggested that solid-state UV/Vis absorption spectra can be used as a new technique to classify salts and cocrystals.

Crystal structure and energetic features of the cocrystal of carbamazepine with 3,5-dinitrobenzoic acid

The synthesis and detailed description of the crystal structure and energetic features of the 1:1 cocrystal of carbamazepine (5H-dibenzo[b,f]azepine-5-carboxamide, CBZ) with 3,5-dinitrobenzoic acid (35DNBA), i.e. C₁₅H₁₂N₂O·C₇H₄N₂O₆, are reported. The CBZ and 35DNBA molecules are packed in alternately arranged layers. Two characteristic R₂²(8) and R₂²(16) hydrogen-bond ring motifs have been found. The supramolecular architecture, besides the network of hydrogen bonds, is also stabilized by numerous C-H...π, C=O...π, N-O...π, N-O...C and C=O...N weak intermolecular contacts involving neighbouring molecules in the crystal network. Identified interactions have been discussed in detail on the basis of a structural and energetic analysis. The latter approach, performed using the Pixel and CrystalExplorer programs, yielded additional information about the lattice energy and energetic landscape of the respective interactions in the crystal of CBZ·3DNBA with the evaluation of electrostatic, polarization, repulsion and dispersion terms.

Structural variety of clofaziminium salts: effect of the counter-ion on clofaziminium conformation and crystal packing

Clofazimine is a water-insoluble antimycobacterial agent gaining attention as a treatment for multi-drug resistant and extensively drug-resistant tuberculosis. Novel salts of clofazimine are reported with fumaric, succinic, 2,4-dihydroxybenzoic and terephthalic acids and with saccharin. The salt structures were obtained by single-crystal X-ray diffraction. The salts with 2,4-dihydroxybenzoic acid and with saccharin are solvated (methanol and acetonitrile, respectively). The reaction of clofazimine with terephthalic acid led to two salt cocrystals, one solvated and one non-solvated. These new clofaziminium salts are compared with the currently known ones in terms of crystal packing and clofazimine/ium conformation. Clofaziminium hydrogen succinate presents isostructurality with clofaziminium hydrogen malonate, an already described salt. In the structure of clofaziminium terephthalate terephthalic acid salt cocrystal, solvent evaporation leads to packing and hydrogen-bonding modifications. In all the new structures, the clofaziminium conformation is quite well conserved and steric hindrance is observed around the protonated site. Conformational optimization of clofaziminium reveals that this steric-hindrance energy penalty is compensated for by hydrogen-bond interactions with the salt counter-ions.

Kinetics Study of Cocrystal Formation Between Indomethacin and Saccharin Using High-Shear Granulation With In Situ Raman Spectroscopy

Pharmaceutical manufacturing processes are necessary to make solid dosage form even in cocrystal formation. In an effort to reduce the number of unit operations, high-shear wet granulation with cocrystallization system was proposed. In the present study, indomethacin-saccharin was chosen as a model compound, and the cocrystal formation kinetics was investigated during the consistent process. The role of each initial indomethacin crystal state (γ-form, α-form, or amorphous) for the kinetics was explored using in situ Raman spectroscopy with multivariate curve resolution by alternating least-squares analysis as a chemometrics. Obtained granules were characterized by X-ray diffraction and tablet dissolution testing. The Raman peaks assigned to indomethacin-saccharin cocrystal were increased with granulation when ethanol was used as a binding solvent. In addition, the reaction kinetics of run samples which had different indomethacin forms was distinguished by best fitting using Avrami-Erofeev or Ginstling-Brounshtein model. The kinetic variance depended on the initial thermodynamic state of indomethacin because they had a different crystallization mechanism for the cocrystal. The scalable and feasible granulation method is required in the pharmaceutical industry.

Preparation of Theophylline-Benzoic Acid Cocrystal and On-Line Monitoring of Cocrystallization Process in Solution by Raman Spectroscopy

Pure theophylline-benzoic acid cocrystal was prepared via slurry and cooling crystallization in solution to overcome the disadvantages of existing preparation methods. The target cocrystal was characterized by powder X-ray diffraction (PXRD), thermalgravimetric analysis (TGA), differential scanning calorimetry (DSC) and Raman spectroscopy. The slurry and cooling cocrystallization process in solution was monitored via on-line Raman spectroscopy. The results obtained from on-line Raman monitoring can exhibit the transformation process from raw materials (theophylline and benzoic acid) to cocrystal and show the cocrystal formation rate. Comparing each transformation process under different conditions in slurry crystallization, we found that suspension density of raw materials and temperature both have an impact on the theophylline-benzoic acid cocrystal formation rate. It could be concluded that the cocrystal formation rate increased with the increase of suspension density of raw materials. Further under the same suspension density, higher temperature will accelerate theophylline-benzoic acid cocrystal formation. Meanwhile, various data from the cocrystallization process in cooling crystallization, including nucleation time, nucleation temperature and suitable cooling ending point can be gained from results of on-line Raman monitoring.

Co-Crystal Formation of Antibiotic Nitrofurantoin Drug and Melamine Co-Former Based on a Vibrational Spectroscopic Study

The co-crystallization of active pharmaceutical ingredients (APIs) has received increasing attention due to the modulation of the relative physicochemical properties of APIs such as low solubility, weak permeability and relatively inferior oral bioavailability. Crystal engineering plays a decisive role in the systematic design and synthesis of co-crystals by means of exerting control on the inter-molecular interactions. The characterization and detection of such co-crystal formations plays an essential role in the field of pharmaceutical research and development. In this work, nitrofurantoin (NF), melamine (MELA) and their hydrated co-crystal form were characterized and analyzed by using terahertz time-domain spectroscopy (THz-TDS) and Raman vibrational spectroscopy. According to the experimental THz spectra, the hydrated co-crystal form has characteristic absorption peaks at 0.67, 1.05, 1.50 and 1.73 THz, while the THz spectra for the two raw parent materials (NF and MELA) are quite different within this spectral region. Similar observations were made from the experimental Raman vibrational spectra results. Density functional theory (DFT) calculation was performed to help determine the major vibrational modes of the hydrated co-crystal between nitrofurantoin and melamine, as well as identify the structural changes due to inter- and/or intra-molecular hydrogen bonding motifs between NF and MELA. The results of the theoretical frequency calculations corroborate the THz and Raman experimental spectra. The characteristic bands of the NF⁻MELA-hydrated co-crystal between nitrofurantoin and melamine were also determined based on the DFT simulated calculation. The reported results in this work provide us with a wealth of structural information and a unique vibrational spectroscopic method for characterizing the composition of specific co-crystals and inter-molecular hydrogen bonding interactions upon pharmaceutical co-crystallization.

Succinic, fumaric, adipic and oxalic acid cocrystals of promethazine hydrochloride

Novel cocrystals of promethazine hydrochloride [PTZ-Cl; systematic name: N,N-dimethyl-1-(10H-phenothiazin-10-yl)propan-2-aminium chloride] with succinic acid (PTZ-Cl-succinic, C₁₇H₂₁N₂S⁺·Cl^-·0.5C₄H₆O₄), fumaric acid (PTZ-Cl-fumaric, C₁₇H₂₁N₂S⁺·Cl^-·0.5C₄H₄O₄) and adipic acid (PTZ-Cl-adipic, C₁₇H₂₁N₂S⁺·Cl^-·0.5C₆H₁₀O₄) were prepared by solvent drop grinding and slow evaporation from acetonitrile solution, along with two oxalic acid cocrystals which were prepared in tetrahydrofuran (the oxalic acid hemisolvate, PTZ-Cl-oxalic, C₁₇H₂₁N₂S⁺·Cl^-·0.5C₂H₂O₄) and nitromethane (the hydrogen oxalate salt, PTZ-oxalic, C₁₇H₂₁N₂S⁺·C₂HO₄^-). The crystal structures obtained by crystallization from tetrahydrofuran and acetonitrile include the Cl^- ion in the lattice structures, while the Cl^- ion is missing from the crystal structure obtained by crystallization from nitromethane (PTZ-oxalic). In order to explain the formation of the two types of supramolecular configurations with oxalic acid, the intermolecular interaction energies were calculated in the presence of the two solvents and the equilibrium configurations were determined using density functional theory (DFT). The cocrystals were studied by X-ray diffraction, IR spectroscopy and differential scanning calorimetry. Additionally, a stability test under special conditions and water solubility were also investigated. PTZ-Cl-succinic, PTZ-Cl-fumaric and PTZ-Cl-adipic crystallized having similar lattice parameter values, and showed a 2:1 PTZ-Cl to dicarboxylic acid stoichiometry. PTZ-Cl-oxalic crystallized in a 2:1 stoichiometric ratio, while the structure lacking the Cl atom belongs has a 1:1 stoichiometry. All the obtained crystals exhibit hydrogen bonds of the type PTZ...Cl...(dicarboxylic acid)...Cl...PTZ, except for PTZ-oxalic, which forms bifurcated bonds between the hydrogen oxalate and promethazinium ions, along with an infinite hydrogen-bonded chain between the hydrogen oxalate anions.

Mechanochemical preparation of molecular and ionic co-crystals of the hormone melatonin

Molecular and ionic co-crystals of melatonin with piperazine, DABCO and CaCl₂ were obtained via kneading with ethanol: the solubility of melatonin in H₂O increases by an order of magnitude when combined with CaCl₂.

Systematic investigation of hydrogen-bond propensities for informing co-crystal design and assembly

Structure-informatics methods can provide important guidelines for defining the experimental space that needs to be explored in the efficient pursuit of new co-crystals.