Pharmaceutical solvates, hydrates and amorphous forms: A special emphasis on cocrystals

Enantiospecific crystallisation behaviour of malic acid in mechanochemical reactions with vinpocetine

We report an intriguing example of enantioselectivity in the formation of new multicomponent crystalline solid containing vinpocetine and malic acid. Several experimental data sets confirmed that the multicomponent system presents a clear enantiospecific crystallisation behaviour both in the solid-state and in solution: only the system consisting of vinpocetine and L-malic acid produces a free-flowing solid consisting of a new crystalline form, while the experiments with D-malic acid produced an amorphous and often deliquescent material. The new vinpocetine-L-malic system crystallizes in the monoclinic space group of P21 and in a 1:1 M ratio, where the two molecules are linked through intermolecular hydrogen bonds in the asymmetric unit. The vinpocetine-DL-malic system was partially crystalline (with also traces of unreacted vinpocetine) with diffraction peaks corresponding to those of vinpocetine-L-malic acid. Solid-state NMR experiments revealed strong ionic interactions in all the three systems. However, while vinpocetine-L-malic acid system was a pure and crystalline phase, in the other two systems the presence of unreacted vinpocetine was always detected. This resulted in a significant worsening of the dissolution profile with respect to vinpocetine-L-malic pure crystalline salt, whose dissolution kinetics appeared superior.

Investigating Internalization of Reporter-Protein-Functionalized Polyhedrin Particles by Brain Immune Cells

Achieving sustained drug delivery to the central nervous system (CNS) is a major challenge for neurological injury and disease, and various delivery vehicles are being developed to achieve this. Self-assembling polyhedrin crystals (POlyhedrin Delivery System; PODS) are being exploited for the delivery of therapeutic protein cargo, with demonstrated efficacy in vivo. However, to establish the utility of PODS for neural applications, their handling by neural immune cells (microglia) must be documented, as these cells process and degrade many biomaterials, often preventing therapeutic efficacy. Here, primary mouse cortical microglia were cultured with a GFP-functionalized PODS for 24 h. Cell counts, cell morphology and Iba1 expression were all unaltered in treated cultures, indicating a lack of acute toxicity or microglial activation. Microglia exhibited internalisation of the PODS, with both cytosolic and perinuclear localisation. No evidence of adverse effects on cellular morphology was observed. Overall, 20-40% of microglia exhibited uptake of the PODS, but extracellular/non-internalised PODS were routinely present after 24 h, suggesting that extracellular drug delivery may persist for at least 24 h.

Development and approval of novel injectables: enhancing therapeutic innovations

INTRODUCTION

Novel injectables possess applications in both local and systemic therapeutics delivery. The advancement in utilized materials for the construction of complex injectables has tremendously upgraded their safety and efficacy.

AREAS COVERED

This review focuses on various strategies to produce novel injectables, including oily dispersions, in situ forming implants, injectable suspensions, microspheres, liposomes, and antibody-drug conjugates. We herein present a detailed description of complex injectable technologies and their related drug formulations permitted for clinical use by the United States Food and Drug Administration (USFDA). The excipients used, their purpose and the challenges faced during manufacturing such formulations have been critically discussed.

EXPERT OPINION

Novel injectables can deliver therapeutic agents in a controlled way at the desired site. However, several challenges persist with respect to their genericization. Astronomical costs incurred by innovator companies during product development, complexity of the product itself, supply limitations with respect to raw materials, intricate manufacturing processes, patent evergreening, product life-cycle extensions, relatively few and protracted generic approvals contribute to the exorbitant prices and access crunch. Moreover, regulatory guidance are grossly underdeveloped and significant efforts have to be directed toward development of effective characterization techniques.

Nanocrystal technologies in biomedical science: From the bench to the clinic

The pharmaceutical industry is grappling with a pressing crisis in drug development characterized by soaring R&D costs, setbacks in blockbuster drug development due to poor aqueous solubility, and patent-related limitations on newly approved molecules. To combat these challenges, diverse strategies have emerged to enhance the solubility and dissolution rates of Biopharmaceutics Classification System (BCS) II and IV drug molecules. Enter drug nanocrystals, a revolutionary nanotechnology-driven, carrier-free colloidal drug delivery system. This review provides a comprehensive insight into nanocrystal strategies, stabilizer selection criteria, preparation methods, advanced characterization techniques, the evolving nanocrystal technological landscape, current market options, and exciting clinical prospects for reshaping the future of pharmaceuticals.

An unusual ionic cocrystal of ponatinib hydrochloride: characterization by single-crystal X-ray diffraction and ultra-high field NMR spectroscopy

This study describes the discovery of a unique ionic cocrystal of the active pharmaceutical ingredient (API) ponatinib hydrochloride (pon·HCl), and characterization using single-crystal X-ray diffraction (SCXRD) and solid-state NMR (SSNMR) spectroscopy. Pon·HCl is a multicomponent crystal that features an unusual stoichiometry, with an asymmetric unit containing both monocations and dications of the ponatinib molecule, three water molecules, and three chloride ions. Structural features include (i) a charged imidazopyridazine moiety that forms a hydrogen bond between the ponatinib monocations and dications and (ii) a chloride ion that does not feature hydrogen bonds involving any organic moiety, instead being situated in a "square" arrangement with three water molecules. Multinuclear SSNMR, featuring high and ultra-high fields up to 35.2 T, provides the groundwork for structural interpretation of complex multicomponent crystals in the absence of diffraction data. A 13C CP/MAS spectrum confirms the presence of two crystallographically distinct ponatinib molecules, whereas 1D 1H and 2D 1H-1H DQ-SQ spectra identify and assign the unusually deshielded imidazopyridazine proton. 1D 35Cl spectra obtained at multiple fields confirm the presence of three distinct chloride ions, with density functional theory calculations providing key relationships between the SSNMR spectra and H⋯Cl- hydrogen bonding arrangements. A 2D 35Cl → 1H D-RINEPT spectrum confirms the spatial proximities between the chloride ions, water molecules, and amine moieties. This all suggests future application of multinuclear SSNMR at high and ultra-high fields to the study of complex API solid forms for which SCXRD data are unavailable, with potential application to heterogeneous mixtures or amorphous solid dispersions.

New Perspectives for Antihypertensive Sartans as Components of Co-crystals and Co-amorphous Solids with Improved Properties and Multipurpose Activity

Sartans (angiotensin II receptor blockers, ARBs), drugs used in the treatment of hypertension, play a principal role in addressing the global health challenge of hypertension. In the past three years, their potential use has expanded to include the possibility of their application in the treatment of COVID-19 and neurodegenerative diseases (80 clinical studies worldwide). However, their therapeutic efficacy is limited by their poor solubility and bioavailability, prompting the need for innovative approaches to improve their pharmaceutical properties. This review discusses methods of co-crystallization and co-amorphization of sartans with nonpolymeric, low molecular, and stabilizing co-formers, as a promising strategy to synthesize new multipurpose drugs with enhanced pharmaceutical properties. The solid-state forms have demonstrated the potential to address the poor solubility limitations of conventional sartan formulations and offer new opportunities to develop dual-active drugs with broader therapeutic applications. The review includes an in-depth analysis of the co-crystal and co-amorphous forms of sartans, including their properties, possible applications, and the impact of synthetic methods on their pharmacokinetic properties. By shedding light on the solid forms of sartans, this article provides valuable insights into their potential as improved drug formulations. Moreover, this review may serve as a valuable resource for designing similar solid forms of sartans and other drugs, fostering further advances in pharmaceutical research and drug development.

Desolvation Processes in Channel Solvates of Niclosamide

The antiparasitic drug niclosamide (NCL) is notable for its ability to crystallize in multiple 1:1 channel solvate forms, none of which are isostructural. Here, using a combination of time-resolved synchrotron powder X-ray diffraction and thermogravimetry, the process-induced desolvation mechanisms of methanol and acetonitrile solvates are investigated. Structural changes in both solvates follow a complicated molecular-level trajectory characterized by a sudden shift in lattice parameters several degrees below the temperature where the desolvated phase first appears. Model fitting of kinetic data obtained under isothermal heating conditions suggests that the desolvation is rate-limited by the nucleation of the solvent-free product. The desolvation pathways identified in these systems stand in contrast to previous investigations of the NCL channel hydrate, where water loss by diffusion initially yields an anhydrous isomorph that converts to the thermodynamic polymorph at significantly higher temperatures. Taking the view that each solvate lattice is a unique "pre-organized" precursor, a comparison of the pathways from different starting topologies to the same final product provides the opportunity to reevaluate assumptions of how various factors (e.g., solvent binding strength, density) influence solid-state desolvation processes.

Using singular value decomposition to analyze drug/β-cyclodextrin mixtures: insights from X-ray powder diffraction patterns

The article discusses the use of mathematical models and linear algebra to understand the crystalline structures and interconversion pathways of drug complexes with β-cyclodextrin (β-CD). It involved the preparation and analysis of mixtures of indomethacin, diclofenac, famotidine, and cimetidine with β-CD using techniques such as differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), and proton nuclear magnetic resonance (1H-NMR). Singular value decomposition (SVD) analysis is used to identify the presence of different polymorphs in the mixtures of these drugs and β-CD, determine interconversion pathways, and distinguish between different forms. In general, linear algebra or artificial intelligence (AI) is used to approximate the contribution of distinguishable entities to various phenomena. We expected linear algebra to completely reveal all eight entities present in the diffractogram dataset. However, after performing the SVD procedure, we found that only six independent basis functions were extracted, and the entities of the INM α-form and the CIM B-form were not included. It is considered that this is due to that data processing is limited to revealing only six or seven independent factors, as it is a small world. The authors caution that these may not always reproduce or approach reality in complicated real-world situations.

One Step In Situ Co-Crystallization of Dapsone and Polyethylene Glycols during Fluidized Bed Granulation

Several studies have demonstrated the feasibility of in situ co-crystallization in different pharmaceutical processes such as spray drying, hot melt extrusion, and fluidized bed granulation (FBG) to produce co-crystal-in-excipient formulations. However, no previous studies have examined such a one step in situ co-crystallization process for co-crystal formulations where the coformer is a polymer. In the current study, we explored the use of FBG to produce co-crystal granules of dapsone (DAP) and different molecular weight polyethylene glycols (PEGs). Solvent evaporation (SE) was proven to generate DAP-PEGs co-crystals at a particular weight ratio of 55:45 w/w between DAP and PEG, which was subsequently used in FBG, using microcrystalline cellulose and hydroxypropyl methyl cellulose as filler excipient and binder, respectively. FBG could generate co-crystals with higher purity than SE. Granules containing DAP-PEG 400 co-crystal could be prepared without any additional binder. DAP-PEG co-crystal granules produced by FBG demonstrated superior pharmaceutical properties, including flow properties and tableting properties, compared to DAP and DAP-PEG co-crystals prepared by SE. Overall, in situ co-crystallization via FBG can effectively produce API-polymer co-crystals and enhance the pharmaceutical properties.

In Situ Cocrystallization via Spray Drying with Polymer as a Strategy to Prevent Cocrystal Dissociation

The aim of the present study was to investigate how different polymers affect the dissociation of cocrystals prepared by co-spray-drying active pharmaceutical ingredient (API), coformer, and polymer. Diclofenac acid-l-proline cocrystal (DPCC) was selected in this study as a model cocrystal due to its previously reported poor physical stability in a high-humidity environment. Polymers investigated include polyvinylpyrrolidone (PVP), poly(1-vinylpyrrolidone-co-vinyl acetate) (PVPVA), hydroxypropyl methyl cellulose, hydroxypropylmethylcellulose acetate succinate, ethyl cellulose, and Eudragit L-100. Terahertz Raman spectroscopy (THz Raman) and powder X-ray diffraction (PXRD) were used to monitor the cocrystal dissociation rate in a high-humidity environment. A Raman probe was used in situ to monitor the extent of the dissociation of DPCC and DPCC in crystalline solid dispersions (CSDs) with polymer when exposed to pH 6.8 phosphate buffer and water. The solubility of DPCC and solid dispersions of DPCC in pH 6.8 phosphate buffer and water was also measured. The dissociation of DPCC was water-mediated, and more than 60% of DPCC dissociated in 18 h at 40 °C and 95% RH. Interestingly, the physical stability of the cocrystal was effectively improved by producing CSDs with polymers. The inclusion of just 1 wt % polymer in a CSD with DPCC protected the cocrystal from dissociation over 18 h under the same conditions. Furthermore, the CSD with PVPVA was still partially stable, and the CSD with PVP was stable (undissociated) after 7 days. The superior stability of DPCC in CSDs with PVP and PVPVA was also demonstrated when systems were exposed to water or pH 6.8 phosphate buffer and resulted in higher dynamic solubility of the CSDs compared to DPCC alone. The improvement in physical stability of the cocrystal in CSDs was thought to be due to an efficient mixing between polymer and cocrystal at the molecular level provided by spray drying and in situ gelling of polymer. It is hypothesized that polymer chains could undergo gelling in situ and form a physical barrier, preventing cocrystal interaction with water, which contributes to slowing down the water-mediated dissociation.

Formation of Hemihydrate Crystal form Overcomes Milling Issue Induced by Exposed Functional Groups on Cleavage Plane for a Y5 Receptor Antagonist of Neuropeptide Y

This study aimed to investigate the crystal forms of an originally designed Y5 receptor antagonist of neuropeptide Y. Polymorphic screening was performed via solvent evaporation and slurry conversion using various solvents. The obtained crystal forms α, β, and γ were characterized by X-ray powder diffraction analysis. Thermal analysis determined that forms α, β, and γ were hemihydrate, metastable and stable forms, respectively; the hemihydrate and the stable forms were candidates. To arrange the particle size, forms α and γ were subjected to jet milling. However, form γ could not be milled because of powder stiction to the apparatus, whereas form α could be. To investigate this mechanism, single-crystal X-ray diffraction analysis was performed. The crystal structure of form γ was characterized by two-dimensional hydrogen bonding between neighboring molecules. This revealed that the functional groups forming hydrogen bonds were exposed on the cleavage plane of form γ. The three-dimensional hydrogen-bonding network with water stabilized the hemihydrate form, α. These results indicate that the hydrogen bondable groups exposed on the cleavage plane of form γ should result in stiction of the powder and adherence to the apparatus. It was concluded that crystal conversion is a method to overcome the milling issue.

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.

Norfloxacin Cocrystals: Mechanochemical Synthesis and Scale-up Viability Through Solubility Studies

Cocrystals are recognized as one of the most efficient approaches to improve aqueous solubility of Biopharmaceutical Classification System, BCS, classes II and IV drugs. Cocrystal discovery and the establishment of experimental conditions suitable for scale-up purposes are some of the main challenges in cocrystal investigation. In this work, the investigation of mechanochemical synthesis of norfloxacin cocrystals with picolinic and isonicotinic acids is performed, leading to the discovery of two new cocrystals of this important BCS class IV antibiotic, which were characterized through thermal, spectral and diffractometric analysis. Norfloxacin apparent aqueous solubility using the cocrystals is also presented, with higher values being obtained for all the investigated systems when compared to the pure drug. Norfloxacin has 3 polymorphs and several solvents/hydrates, which represents a challenge for obtaining pure cocrystal forms from solvent crystallization. This challenge was successfully overcome in this work, as experimental conditions to obtain the pure cocrystals (the new ones and also norfloxacin-nicotinic acid and norfloxacin-saccharin) were established using Crystal16 equipment. This is a crucial step to envisage future scale-up procedures and therefore a valuable information for the pharmaceutical industry.

Evidence of a New Crystalline Phase of Prednisolone Obtained from the Study of the Hydration-Dehydration Mechanisms of the Sesquihydrate

The dehydration of prednisolone sesquihydrate is studied and characterized by different physico-chemical analysis methods. The meticulous study of this dehydration led to the highlighting of a new solid form (form 3), metastable, never identified before. In a second step, the rehydration of anhydrous forms 1 and 2 of prednisolone is studied, in particular by Dynamic Vapor Sorption. It is then demonstrated that neither of the two forms is sensitive to humidity. By means of solid-gas equilibria, the sesquihydrate can only be obtainable from the isomorphic anhydrous form. Finally, a classification of the sesquihydrate is made, taking into account, in particular, the activation energy determined during dehydration.

How much do molecular shapes matter?

Nifedipine (NIF) molecules (L-type calcium channel antagonists) pack in solvated structures showing strikingly similar patterns, see Jones et al. [Acta Cryst. (2023), B79, 164-175]. How much do molecular shapes, such as the NIF molecule which resembles the letter T, matter in their associations in crystals?

New Lidocaine-Based Pharmaceutical Cocrystals: Preparation, Characterization, and Influence of the Racemic vs. Enantiopure Coformer on the Physico-Chemical Properties

This study describes the preparation, characterization, and influence of the enantiopure vs. racemic coformer on the physico-chemical properties of a pharmaceutical cocrystal. For that purpose, two new 1:1 cocrystals, namely lidocaine:dl-menthol and lidocaine:d-menthol, were prepared. The menthol racemate-based cocrystal was evaluated by means of X-ray diffraction, infrared spectroscopy, Raman, thermal analysis, and solubility experiments. The results were exhaustively compared with the first menthol-based pharmaceutical cocrystal, i.e., lidocaine:l-menthol, discovered in our group 12 years ago. Furthermore, the stable lidocaine/dl-menthol phase diagram has been screened, thoroughly evaluated, and compared to the enantiopure phase diagram. Thus, it has been proven that the racemic vs. enantiopure coformer leads to increased solubility and improved dissolution of lidocaine due to the low stable form induced by menthol molecular disorder in the lidocaine:dl-menthol cocrystal. To date, the 1:1 lidocaine:dl-menthol cocrystal is the third menthol-based pharmaceutical cocrystal, after the 1:1 lidocaine:l-menthol and the 1:2 lopinavir:l-menthol cocrystals reported in 2010 and 2022, respectively. Overall, this study shows promising potential for designing new materials with both improved characteristics and functional properties in the fields of pharmaceutical sciences and crystal engineering.

Non-stoichiometric carbamazepine cocrystal hydrates of 3,4-/3,5-dihydroxybenzoic acids: coformer-water exchange

The cocrystallisation of carbamazepine (CBZ) with 3,4-/3,5-dihydroxybenzoic acids (34/35DHBA) with different stoichiometries formed molecular alloys, exchanging a water molecule, in their isostructural CBZ dihydrate form. Furthermore, we show a correlation between the mechanical properties of the CBZ-DHBA cocrystals with the amount of coformer present.

Dehydration kinetics and mechanism of the stable isonicotinamide hydrate revealed by terahertz spectroscopy and DFT calculation

The dehydration behavior of pharmaceutical hydrates has a great influence on its physiochemical properties such as stability, dissolution rate and bioavailability. However, how the intermolecular interactions vary during dehydration process remains elusive. In this work, we employed terahertz time-domain spectroscopy (THz-TDS) to probe the low-frequency vibrations and the dehydration process of isonicotinamide hydrate I (INA-H I). Theoretical solid-state DFT calculation was conducted to reveal its mechanism. Vibrational modes which are responsible for the THz absorption peaks were decomposed for better understanding the characters of these low-frequency modes. The result suggests translational motion is the dominant component for water molecules in THz region. Evolution of the THz spectrum of INA-H I during dehydration provides direct evidence of the variations of crystal structure. Based on the THz measurements, a two-step kinetics mode including first-rate reaction and three-dimensional nuclei growth is proposed. And we nure that the low-frequency vibrations of water molecules are the origin of dehydration process of hydrate.

Formulation Approaches to Crystalline Status Modification for Carotenoids: Impacts on Dissolution, Stability, Bioavailability, and Bioactivities

Carotenoids, including carotenes and xanthophylls, have been identified as bioactive ingredients in foods and are considered to possess health-promoting effects. From a biopharmaceutical perspective, several physicochemical characteristics, such as scanty water solubility, restricted dissolution, and susceptibility to oxidation may influence their oral bioavailability and eventually, their effectiveness. In this review, we have summarized various formulation approaches that deal with the modification of crystalline status for carotenoids, which may improve their physicochemical properties, oral absorption, and biological effects. The mechanisms involving crystalline alteration and the typical methods for examining crystalline states in the pharmaceutical field have been included, and representative formulation approaches are introduced to unriddle the mechanisms and effects more clearly.

Recent Advances in Pharmaceutical Cocrystals: A Focused Review of Flavonoid Cocrystals

Cocrystallization is currently an attractive technique for tailoring the physicochemical properties of active pharmaceutical ingredients (APIs). Flavonoids are a large class of natural products with a wide range of beneficial properties, including anticancer, anti-inflammatory, antiviral and antioxidant properties, which makes them extensively studied. In order to improve the properties of flavonoids, such as solubility and bioavailability, the formation of cocrystals may be a feasible strategy. This review discusses in detail the possible hydrogen bond sites in the structure of APIs and the hydrogen bonding networks in the cocrystal structures, which will be beneficial for the targeted synthesis of flavonoid cocrystals. In addition, some successful studies that favorably alter the physicochemical properties of APIs through cocrystallization with coformers are also highlighted here. In addition to improving the solubility and bioavailability of flavonoids in most cases, flavonoid cocrystals may also alter their other properties, such as anti-inflammatory activity and photoluminescence properties.

Synthesis, Crystal Packing Aspects and Pseudosymmetry in Coordination Compounds with a Phosphorylamide Ligand

This work reports the synthesis and crystal structure of new closely related coordination compounds, [ML2]·nTHF, where M is Zn or Mn; L is a phosphorylmethylamide derivative of benzothiadiazole; n = 1 (M = Zn) and 1, 2 (M = Mn); and THF is tetrahydrofuran. The zinc compound, 1·THF, crystallizes in a high-symmetry space group, I41/a, that is relatively rare for compounds with organic ligands. The corresponding manganese congener, 2·THF, with a similar crystal packing, features a pseudosymmetrical structure P21/c of the doubled volume of the unit cell as compared to 1·THF. The main difference between the structures lies in a different arrangement of solvate THF molecules, which likely modulates the crystal packing of the complexes. Another manganese solvatomorph, 2·2THF, reveals a fundamentally different crystal packing while exhibiting a similar geometry of the complex. We consider the problem of localization of solvate THF molecules and the types of their disorder by the example of compounds 1–2.

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.

Seeking Rules Governing Mixed Molecular Crystallization

Mixed crystals result when components of the structure are randomly replaced by analogues in ratios that can be varied continuously over certain ranges. Mixed crystals are useful because their properties can be adjusted by increments, simply by altering the ratio of components. Unfortunately, no clear rules exist to predict when two compounds are similar enough to form mixed crystals containing substantial amounts of both. To gain further understanding, we have used single-crystal X-ray diffraction, computational methods, and other tools to study mixed crystallizations within a selected set of structurally related compounds. This work has allowed us to begin to clarify the rules governing the phenomenon by showing that mixed crystals can have compositions and properties that vary continuously over wide ranges, even when the individual components do not normally crystallize in the same way. Moreover, close agreement of the results of our experiments and computational modeling demonstrates that reliable predictions about mixed crystallization can be made, despite the complexity of the phenomenon.

Baloxavir Marboxil Shows Anomalous Conversion of Crystal Forms from Stable to Metastable through Formation of Specific Solvate Form

Baloxavir marboxil is a novel cap-dependent endonuclease inhibitor of influenza. This study aimed to identify its polymorphs and their relationship with crystal engineering. Polymorph screening by evaporation gave forms I-III and solvate forms IV and V. Heating enabled the conversion of form III to form II, but did not enable that of forms I and II. The solvent-mediated transformation of the forms I-III by magnetic stirring in various solvents resulted in the formation of form I. These results indicate that form I is the stable form. However, all crystal forms transformed to form II after magnetic stirring in a 50% acetonitrile aqueous solution, which was not obtained from water or acetonitrile. The suspension in a 50% acetonitrile aqueous solution exhibited a novel X-ray diffraction pattern as shown in form VI. The measurement of the suspension by solid-state ¹³C-nuclear magnetic resonance revealed that the spectra of forms II and VI were similar. From these results, we conclude that the drug forms a solvate with both water and acetonitrile and spontaneously transforms to form II upon rapid desolvation under ambient conditions. This study elucidates the mechanism of unexpected convergence to a metastable form in a specific solvent and contributes to the crystal engineering of baloxavir marboxil.

Mechanistic study of the formation of arbutin polymorphs and solvates

Six solid forms of arbutin are successfully obtained and four single crystal structures are reported for the first time. Further, the formation mechanism of arbutin solvates is proposed and rationalized.

A Comparison of the Pharmacokinetics and Safety of Dapagliflozin Formate, an Ester Prodrug of Dapagliflozin, to Dapagliflozin Propanediol Monohydrate in Healthy Subjects

Background

Dapagliflozin formate (DAP-FOR, DA-2811), an ester prodrug of dapagliflozin, was developed to improve the stability and pharmaceutical manufacturing process of dapagliflozin, a sodium-glucose cotransporter-2 inhibitor.

Purpose

This study aimed to evaluate the pharmacokinetics (PKs) and safety of dapagliflozin for DAP-FOR compared to those for dapagliflozin propanediol monohydrate (DAP-PDH, Forxiga) in healthy subjects.

Methods

This was an open-label, randomized, single-dose, two-period, two-sequence crossover study. The subjects received a single dose of DAP-FOR or DAP-PDH 10 mg in each period, with a 7-day washout. Serial blood samples for PK analysis were collected up to 48 hours after a single administration to determine plasma concentrations of DAP-FOR and dapagliflozin. PK parameters were calculated using a non-compartmental method and compared between the two drugs.

Results

In total, 28 subjects completed the study. DAP-FOR plasma concentrations were not detected in all of the blood sampling time points except for one time point in one subject, and the corresponding DAP-FOR plasma concentration in the subject was close to the lower limit of quantification. The mean plasma concentration-time profiles of dapagliflozin were comparable between the two drugs. The geometric mean ratios and its 90% confidence intervals of the maximum plasma concentration and area under the plasma concentration-time curve of dapagliflozin for DAP-FOR to DAP-PDH were within the conventional bioequivalence range of 0.80-1.25. Both drugs were well-tolerated, with a similar incidence of adverse drug reactions.

Conclusion

The rapid conversion of DAP-FOR into dapagliflozin led to the extremely low exposure of DAP-FOR and comparable PK profiles of dapagliflozin between DAP-FOR and DAP-PDH. The safety profiles were also similar between the two drugs. These results suggest that DAP-FOR can be used as an alternative to DAP-PDH.

Three-state fluorescence hydrochromism of a fluorophore-spacer-receptor system with variations in relative humidity

The uptake of atmospheric moisture by hygroscopic materials can have marked effects on a material's physical and chemical properties. This is true of materials that go on to incorporate waters of hydration in their molecular structural lattice, forming stable hydrates with fluctuations in relative humidity (RH). Nevertheless, RH remains relatively uncontrolled for a variable that can fluctuate widely depending on geographical climate, weather fluctuations, and building HVAC system stability. Herein, we report a processable 1,8-napthalimide-based fluorophore-spacer-receptor system that unexpectedly exhibited reversible three-state fluorescence hydrochromism with changes in RH due to RH-induced solid state molecular rearrangement. Care should be taken to evaluate the impact of variations in RH when characterising the solid state emission properties of charged fluorescent materials.

Mechanisms of Crystal Plasticization by Lattice Water

PURPOSE

Water of crystallization has been observed to increase plasticity, decrease crystal hardness, and improve powder compressibility and tabletability of organic crystals. This work is aimed at gaining a molecular level insight into this observation.

METHOD

We systematically analyzed crystal structures of five stoichiometric hydrate systems, using several complementary techniques of analysis, including energy framework, water environment, overall packing change, hydrate stability, and slip plane identification.

RESULTS

The plasticizing effect by lattice water is always accompanied by an introduction of more facile slip planes, lower packing efficiency, and lower density in all hydrate systems examined in this work. Three distinct mechanisms include 1) changing the distribution of intermolecular interactions without significantly changing the packing of molecules to introduce more facile slip planes; 2) changing packing feature into a flat layered structure so that more facile slip planes are introduced; 3) reducing the interlayer interaction energies and increasing the anisotropy.

CONCLUSION

Although the specific mechanisms for these five systems differ, all five hydrates are featured with more facile slip planes, lower packing efficiency, and lower density.

Hydrates of active pharmaceutical ingredients: A 35Cl and 2H solid-state NMR and DFT study

This study uses ³⁵Cl and ²H solid-state NMR (SSNMR) spectroscopy and dispersion-corrected plane-wave density functional theory (DFT) calculations to characterize the molecular-level structures and dynamics of hydrates of active pharmaceutical ingredients (APIs). We use ³⁵Cl SSNMR to measure the EFG tensors of the chloride ions to characterize hydrated forms of hydrochloride salts of APIs, along with two corresponding anhydrous forms. DFT calculations are used to refine the crystal structures of the APIs and determine relationships between the ³⁵Cl EFG tensors and the spatial arrangements of proximate hydrogen bonds, which are particularly influenced by interactions with water molecules. We find that the relationship between ³⁵Cl EFG tensors and local hydrogen bonding geometries is complex, but meaningful structure/property relationships can be garnered through use of DFT calculations. Specifically, for every case in which such a comparison could be made, we find that the hydrate has a smaller magnitude of C_Q than the corresponding anhydrous form, indicating a chloride ion environment with a ground-state electron density of higher spherical symmetry in the former. Finally, variable-temperature ³⁵Cl and ²H SSNMR experiments on a deuterium-exchanged sample of the API cimetidine hydrochloride monohydrate are used to monitor temperature-dependent influences on the spectra that may arise from motional influences on the ³⁵Cl and ²H EFG tensors. From the ²H SSNMR spectra, we determine that the motions of water molecules are characterized by jump-like motions about their C₂ rotational axes that occur on timescales that are unlikely to influence the ³⁵Cl central-transition (+1/2 ↔︎ -1/2) powder patterns (this is confirmed by ³⁵Cl SSNMR). Together, these methods show great promise for the future study of APIs in their bulk and dosage forms, especially variable hydrates in which crystallographic water content varies with external conditions such as humidity.

The Structure of Liquid and Glassy Carbamazepine

To enhance the solubility of orally administered pharmaceuticals, liquid capsules or amorphous tablets are often preferred over crystalline drug products. However, little is known regarding the variation in bonding mechanisms between pharmaceutical molecules in their different disordered forms. In this study, liquid and melt-quenched glassy carbamazepine have been studied using high energy X-ray diffraction and modeled using Empirical Potential Structure Refinement. The results show significant structural differences between the liquid and glassy states. The liquid shows a wide range of structures; from isolated molecules, to aromatic ring correlations and NH-O hydrogen bonding. Upon quenching from the liquid to the glass the number of hydrogen bonds per molecule increases by ~50% at the expense of a ~30% decrease in the close contact (non-bonded) carbon-carbon interactions between aromatic rings. During the cooling process, there is an increase in both singly and doubly hydrogen-bonded adjacent molecules. Although hydrogen-bonded dimers found in the crystalline states persist in the glassy state, the absence of a crystalline lattice also allows small, hydrogen-bonded NH-O trimers and tetramers to form. This proposed model for the structure of glassy carbamazepine is consistent with the results from vibrational spectroscopy and nuclear magnetic resonance.

Novel Ascorbic Acid Co-Crystal Formulations for Improved Stability

A series of co-crystals of ascorbic acid were prepared with equimolar amounts of co-crystal formers (CCFs), including isonicotinic acid, nicotinic acid, 3,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid and m-hydroxybenzoic acid, by slow solvent evaporation and solvent-assisted grinding. The co-crystals were characterized by single-crystal X-ray diffraction spectroscopy, powder X-ray diffraction, IR spectroscopy, differential scanning calorimetry and thermogravimetric analysis. Molecular dynamics (MD) simulations further validated the interaction energy and the possible intermolecular hydrogen bonds among VC and CCFs. The co-crystals showed improved stability when exposed to different wavelengths of light, pH and temperatures compared to the free analogue, especially at higher pH (~9) and lower temperature (~4 °C).

19F Solid-state NMR characterization of pharmaceutical solids

Solid-state NMR has been increasingly recognized as a high-resolution and versatile spectroscopic tool to characterize drug substances and products. However, the analysis of pharmaceutical materials is often carried out at natural isotopic abundance and a relatively low drug loading in multi-component systems and therefore suffers from challenges of low sensitivity. The fact that fluorinated therapeutics are well represented in pipeline drugs and commercial products offers an excellent opportunity to utilize fluorine as a molecular probe for pharmaceutical analysis. We aim to review recent advancements of ¹⁹F magic angle spinning NMR methods in modern drug research and development. Applications to polymorph screening at the micromolar level, structural elucidation, and investigation of molecular interactions at the Ångström to submicron resolution in drug delivery, stability, and quality will be discussed.

DFT–Assisted Structure Determination from Powder X-ray Diffraction Data of a New Zonisamide/ϵ-Caprolactam Cocrystal

The crystal structure of a new zonisamide cocrystal, an anticonvulsant drug used to treat the symptoms of epilepsy and Parkinson’s disease, with ϵ-caprolactam is reported herein. The structure has been solved by direct space methodologies from powder X-ray diffraction data. The refinement of the structure was conducted by the Rietveld method assisted by the dispersion-corrected density-functional theory (D-DFT) calculations and periodic boundary conditions. Further analysis of the structure reveals several H-bonded synthons and self–assembled dimers that have been further analyzed by DFT calculations and other computational tools such as molecular electrostatic potential (MEP) surfaces and the quantum theory of “atom-in-molecules” (QTAIM).

Nano- and Crystal Engineering Approaches in the Development of Therapeutic Agents for Neoplastic Diseases

Cancer is a leading cause of death worldwide. It is a global quandary that requires the administration of many different active pharmaceutical ingredients (APIs) with different characteristics. As is the case with many APIs, cancer treatments exhibit poor aqueous solubility which can lead to low drug absorption, increased doses, and subsequently poor bioavailability and the occurrence of more adverse events. Several strategies have been envisaged to overcome this drawback, specifically for the treatment of neoplastic diseases. These include crystal engineering, in which new crystal structures are formed to improve drug physicochemical properties, and/or nanoengineering in which the reduction in particle size of the pristine crystal results in much improved physicochemical properties. Co-crystals, which are supramolecular complexes that comprise of an API and a co-crystal former (CCF) held together by non-covalent interactions in crystal lattice, have been developed to improve the performance of some anti-cancer drugs. Similarly, nanosizing through the formation of nanocrystals and, in some cases, the use of both crystal and nanoengineering to obtain nano co-crystals (NCC) have been used to increase the solubility as well as overall performance of many anticancer drugs. The formulation process of both micron and sub-micron crystalline formulations for the treatment of cancers makes use of relatively simple techniques and minimal amounts of excipients aside from stabilizers and co-formers. The flexibility of these crystalline formulations with regards to routes of administration and ability to target neoplastic tissue makes them ideal strategies for effectiveness of cancer treatments. In this review, we describe the use of crystalline formulations for the treatment of various neoplastic diseases. In addition, this review attempts to highlight the gaps in the current translation of these potential treatments into authorized medicines for use in clinical practice.

Solid-State and Particle Size Control of Pharmaceutical Cocrystals using Atomization-Based Techniques

Poor bioavailability and aqueous solubility represent a major constraint during the development of new API molecules and can influence the impact of new medicines or halt their approval to the market. Cocrystals offer a novel and competitive advantage over other conventional methods with respect towards the substantial improvement in solubility profiles relative to the single-API crystals. Furthermore, the production of such cocrystals through atomization-based methods allow for greater control, with respect to particle size reduction, to further increase the solubility of the API. Such atomization-based methods include supercritical fluid methods, conventional spray drying and electrohydrodynamic atomization/electrospraying. The influence of process parameters such as solution flow rates, pressure and solution concentration, in controlling the solid-state and final particle size are discussed in this review with respect to atomization-based methods. For the last decade, literature has been attempting to catch-up with new regulatory rulings regarding the classification of cocrystals, due in part to data sparsity. In recent years, there has been an increase in cocrystal publications, specifically employing atomization-based methods. This review considers the benefits to employing atomization-based methods for the generation of pharmaceutical cocrystals, examines the most recent regulatory changes regarding cocrystals and provides an outlook towards the future of this field.

The fingerprints of nifedipine/isonicotinamide cocrystal polymorph studied by terahertz time-domain spectroscopy

Cocrystal is constructed to improve physicochemical properties of active pharmaceutical ingredient and prevent polymorphism via intermolecular interactions. However, recent examples on cocrystal polymorphs display significantly different properties. Even though some analytical techniques have been used to characterize the cocrystal polymorphic system, it remains unclear how intermolecular interactions drive and stabilize the structure. In this work, we study the cocrystal polymorphs of nifedipine (NFD) and isonicotinamide (INA) using terahertz (THz) spectroscopy. Form I and form II of NFD-INA cocrystals show spectral fingerprints in THz region. Temperature-dependent THz spectra display distinguished frequency shifts of each fingerprint. Combined with solid-state density functional theory (DFT) calculations, the experimental fingerprints and their distinct responses to temperature are elucidated by specific collective vibrational modes. The vibrations of hydrogen bonding between dihydropyridine ring of NFD and INA are generally distributed below 1.5 THz, which play important roles in stabilizing cocrystal and preventing the oxidation of NFD. The rotations of methyl group in NFD are widely distributed in the range of 1.5-4.0 THz, which helps the steric recognition. The results demonstrate that THz spectroscopy is a sensitive tool to discriminate cocrystal polymorphs. It has the potential to be used as a non-invasive technique for pharmaceutical screening.

A High Energy X-ray Diffraction Study of Amorphous Indomethacin

Amorphous pharmaceuticals often possess a wide range of molecular conformations and bonding arrangements. The x-ray pair distribution function (PDF) method is a powerful technique for the characterization of variations in both intra-molecular and inter-molecular packing arrangements. Here, the x-ray PDF of amorphous Indomethacin is shown to be particularly sensitive to the preferred orientations of the chlorobenzyl ring found in isomers in the crystalline state. In some cases, the chlorobenzyl ring has no preferred torsional angle in the amorphous form, while in others evidence of distinct isomer orientations are observed. Amorphous samples with no preferred torsion angles of the chlorobenzyl ring are found to favor enhanced inter-molecular hydrogen bonding, and this is reflected in the intensity of the first sharp diffraction peak. These significant variations in structure rule out amorphous Indomethacin as a possible standard for x-ray PDF measurements. At high humidity, time resolved PDF's for >40 h reveal water molecules forming hydrogen bonds with Indomethacin molecules. A simple linear hydrogen bond model indicates that water molecules in the wet amorphous form have similar hydrogen bond strengths to those found between Indomethacin dimers or chains in the dry amorphous form.

Kinetic solubility improvement and influence of polymers on controlled supersaturation of itraconazole-succinic acid nano-co-crystals

Nano-co-crystals enhance the solubility and dissolution rate of poorly soluble drugs. The objective of this study was to obtain a better understanding of the dissolution process of nano-co-crystals and of the precipitation inhibition by various polymers. Itraconazole-succinic acid (ITZ-SUC) nano-co-crystal was chosen as model drug formulation to investigate the supersaturation and precipitation inhibition capabilities of various polymers (HPMC E5, HPMC E50, HPMCAS, HPC-SSL, PVPK30 and PVPVA64). The kinetic concentration-time profiles of nano-co-crystal were measured under non-sink conditions with in situ UV-VIS spectroscopy. HPMC E5 performed best by achieving the greatest extended supersaturation/precipitation inhibition. The precipitation inhibition capacity of HPMC E5 was proportional to its concentration. The maximum achievable supersaturation was proportional to the dissolution rate which can be modulated by the rate of supersaturation generation (i.e., addition rate or dose). Supersaturation could be prolonged significantly resulting in 2-5-fold increased area under the dissolution curves compared to nano-co-crystals alone. This effect was limited by a critical excess of undissolved particles with high specific surface area which acted as crystallization seeds resulting in faster precipitation. The study highlighted that a faster dissolution rate and the use of precipitation inhibitors were two key factors determining the extent and time of supersaturation of nano-co-crystals.

Two anhydrous forms and one monohydrate of a cocrystal of axitinib and glutaric acid: characterization, property evaluation and phase transition study

The polymorphs and hydrates of multi-component crystals have not been studied as extensively as that of single-component crystals. In this work, one anhydrate and one monohydrate of a cocrystal involving...