Solid forms of pharmaceuticals: Polymorphs, salts and cocrystals

Evaluating experimental, knowledge-based and computational cocrystal screening methods to advance drug-drug cocrystal fixed-dose combination development

Fixed-dose combinations (FDCs) offer significant advantages to patients and the pharmaceutical industry alike through improved dissolution profiles, synergistic effects and extended patent lifetimes. Identifying whether two active pharmaceutical ingredients have the potential to form a drug-drug cocrystal (DDC) or interact is an essential step in determining the most suitable type of FDC to formulate. The lack of coherent strategies to determine if two active pharmaceutical ingredients that can be co-administered can form a cocrystal, has significantly impacted DDC commercialisation. This review aims to accelerate the development of FDCs and DDCs by evaluating existing experimental, knowledge-based and computational cocrystal screening methods; the background of their development, their application in screening for cocrystals and DDCs, and their limitations are discussed. The evaluation provided in this review will act as a guide for selecting suitable screening methods to accelerate FDC development.

In Situ Eutectic Formation in a Polymeric Matrix via Hot-Melt Reactive Extrusion and the Use of Partial Least Squares Regression Modeling for Reaction Yield Determination

There has been a significant volume of work investigating the design and synthesis of new crystalline multicomponent systems via examining complementary functional groups that can reliably interact through the formation of noncovalent bonds, such as hydrogen bonds (H-bonds). Crystalline multicomponent molecular adducts formed using this approach, such as cocrystals, salts, and eutectics, have emerged as drug product intermediates that can lead to effective drug property modifications. Recent advancement in the production for these multicomponent molecular adducts has moved from batch techniques that rely upon intensive solvent use to those that are solvent-free, continuous, and industry-ready, such as reactive extrusion. In this study, a novel eutectic system was found when processing albendazole and maleic acid at a 1:2 molar ratio and successfully prepared using mechanochemical methods including liquid-assisted grinding and hot-melt reactive extrusion. The produced eutectic was characterized to exhibit a 100 °C reduction in melting temperature and enhanced dissolution performance (>12-fold increase at 2 h point), when compared to the native drug compound. To remove handling of the eutectic as a formulation intermediate, an end-to-end continuous-manufacturing-ready process enables feeding of the raw parent reagents in their respective natural forms along with a chosen polymeric excipient, Eudragit EPO. The formation of the eutectic was confirmed to have taken place in situ in the presence of the polymer, with the reaction yield determined using a multivariate calibration model constructed by combining spectroscopic analysis with partial least-squares regression modeling. The ternary extrudates exhibited a dissolution profile similar to that of the 1:2 prepared eutectic, suggesting a physical distribution (or suspension) of the in situ synthesized eutectic contents within the polymeric matrix.

Ionic Liquids in Pharmaceutical and Biomedical Applications: A Review

The unique properties of ionic liquids (ILs), such as structural tunability, good solubility, chemical/thermal stability, favorable biocompatibility, and simplicity of preparation, have led to a wide range of applications in the pharmaceutical and biomedical fields. ILs can not only speed up the chemical reaction process, improve the yield, and reduce environmental pollution but also improve many problems in the field of medicine, such as the poor drug solubility, product crystal instability, poor biological activity, and low drug delivery efficiency. This paper presents a systematic and concise analysis of the recent advancements and further applications of ILs in the pharmaceutical field from the aspects of drug synthesis, drug analysis, drug solubilization, and drug crystal engineering. Additionally, it explores the biomedical field, covering aspects such as drug carriers, stabilization of proteins, antimicrobials, and bioactive ionic liquids.

Effect of Basic Amino Acids on Folic Acid Solubility

To prevent neural tube defects and other cardiovascular diseases in newborns, folic acid (FA) is recommended in pregnant women. A daily dose of 600 µg FA consumption is widely prescribed for women during pregnancy and 400 µg for women with childbearing potential. FA is a class IV compound according to the Biopharmaceutics Classification System (BCS) due to its low permeability (1.7 × 10-6 cm/s) and low solubility (1.6 mg/L); therefore, it must be administered via a formulation that enhances its solubility. Studies reported in the literature have proved that co-amorphization and salt formation of a poorly soluble drug with amino acids (AA) can significantly increase its solubility. Although arginine has been used with FA as a supplement, there is no information on the effect of basic AA (arginine and lysine) on the physical and chemical properties of FA-AA binary formulations. The present study implemented a conductimetric titration methodology to find the effective molar ratio to maximize FA solubility. The results showed that a 1:2.5 FA:AA molar ratio maximized solubility for arginine and lysine. Binary formulations were prepared using different methods, which led to an amorphous system confirmed by the presence of a glass transition, broad FTIR bands, and the absence of an X-ray diffraction pattern. Results of FA:AA (1:2.5) solubility increased in the range of 5500-6000 times compared with pure FA. In addition to solubility enhancement, the binary systems presented morphological properties that depend on the preparation method and whose consideration could be strategic for scaling purposes.

Conformational Trimorphism in an Ionic Cocrystal of Hesperetin

We report the existence of conformational polymorphism in an ionic cocrystal (ICC) of the nutraceutical compound hesperetin (HES) in which its tetraethylammonium (TEA⁺) salt serves as a coformer. Three polymorphs, HESTEA-α, HESTEA-β and HESTEA-γ, were characterized by single-crystal X-ray diffraction (SCXRD). Each polymorph was found to be sustained by phenol···phenolate supramolecular heterosynthons that self-assemble with phenol···phenol supramolecular homosynthons into C ₃ ²(7) H-bonded motifs. Conformational variability in HES moieties and different relative orientations of the H-bonded motifs resulted in distinct crystal packing patterns: HESTEA-α and HESTEA-β exhibit H-bonded sheets; HESTEA-γ is sustained by bilayers of H-bonded tapes. All three polymorphs were found to be stable upon exposure to humidity under accelerated stability conditions for 2 weeks. Under competitive slurry conditions, HESTEA-α was observed to transform to the β or γ forms. Solvent selection impacted the relationship between HESTEA-β (favored in EtOH) and HESTEA-γ (favored in MeOH). A mixture of the β and γ forms was found to be present following H₂O slurry.

Design of Ascorbic Acid Eutectic Mixtures With Sugars to Inhibit Oxidative Degradation

L-Ascorbic acid (ASC), commonly known as vitamin C, acts as an anti-oxidant in the biological system. It is extensively used as an excipient in pharmaceutical industry, food supplements in fruit juices, and food materials due to its free radicals scavenging activity. Main drawback of ASC is its poor aqueous stability owing to the presence of lactone moiety that is easily oxidized to dehydroascorbic acid and further degraded. To improve aqueous stability and inhibit oxidative degradation, ASC was co-crystallized to constitute binary eutectic compositions with mono and di-saccharides such as glucose, sucrose, lactose, and mannitol. The eutectics were confirmed by their (single) lower melting endotherm compared to ASC and sugars, although Powder X-ray diffraction (PXRD) and Fourier transform Infrared spectroscopy (FT-IR) data confirmed the characteristics of their physical mixture. Scanning electron microscope (SEM) images of the binary eutectics confirmed their irregular morphology. The ASC eutectics exhibited improved shelf-life by 2–5-fold in weakly acidic (pH 5) and neutral (pH 7) aqueous buffer medium, whereas the eutectic with glucose enhanced shelf-life only by 1.1–1.2-fold in acidic medium (pH 3.3 and 4). Notably, stabilizing effect of the sugar eutectics decreased with increasing acidity of the medium. In addition, higher binding energy of the disaccharide eutectics partially supports the aqueous stability order of ASC in the neutral pH medium due to more number of non-bonded interactions than that of monosaccharides.

Multicomponent Crystal of Metformin and Barbital: Design, Crystal Structure Analysis and Characterization

The formation of most multicomponent crystals relies on the interaction of hydrogen bonds between the components, so rational crystal design based on the expected hydrogen-bonded supramolecular synthons was employed to establish supramolecular compounds with desirable properties. This theory was put into practice for metformin to participate in more therapeutic fields to search for a fast and simple approach for the screening of candidate crystal co-formers. The prediction of intermolecular synthons facilitated the successful synthesis of a new multicomponent crystal of metformin (Met) and barbital (Bar) through an anion exchange reaction and cooling crystallization method. The single crystal X-ray diffraction analysis demonstrated the hydrogen bond-based ureide/ureide and guanidine/ureide synthons were responsible for the self-assembly of the primary structural motif and extended into infinite supramolecular heterocatemeric structures.

Mechanochemistry: A Green Approach in the Preparation of Pharmaceutical Cocrystals

Mechanochemistry is considered an alternative attractive greener approach to prepare diverse molecular compounds and has become an important synthetic tool in different fields (e.g., physics, chemistry, and material science) since is considered an ecofriendly procedure that can be carried out under solvent free conditions or in the presence of minimal quantities of solvent (catalytic amounts). Being able to substitute, in many cases, classical solution reactions often requiring significant amounts of solvents. These sustainable methods have had an enormous impact on a great variety of chemistry fields, including catalysis, organic synthesis, metal complexes formation, preparation of multicomponent pharmaceutical solid forms, etc. In this sense, we are interested in highlighting the advantages of mechanochemical methods on the obtaining of pharmaceutical cocrystals. Hence, in this review, we describe and discuss the relevance of mechanochemical procedures in the formation of multicomponent solid forms focusing on pharmaceutical cocrystals. Additionally, at the end of this paper, we collect a chronological survey of the most representative scientific papers reporting the mechanochemical synthesis of cocrystals.

Cocrystals of Apixaban with Improved Solubility and Permeability: Formulation, Physicochemical Characterization, Pharmacokinetic Evaluation, and Computational Studies

The objective of the current study was to develop new cocrystals of Apixaban (APX) to improve its solubility and permeability. The molecular interaction between APX and caffeine (CFFN) was further studied by Raman spectroscopy. The results of all eight studied conformers revealed that the synthesized APX-CFFN cocrystals had the highest solubility and permeability. The water solubility and permeability of APX in the cocrystal were simultaneously enhanced as compared with pure APX in the physiological pH environment (pH 6.8 and pH 7.4). The X-ray diffraction analysis revealed that the cocrystal has a component molar ratio of 1:1. This was dominated by a three-dimensional hydrogen bonding supramolecular structure. The in vivo pharmacokinetic (PK) study indicated that the mean area under curve (AUC) of APX from the synthesized cocrystal was enhanced more than three-folds than the pure APX. Tablets of APX and APX-CFFN cocrystals were prepared using direct compression method and evaluated for in vitro dissolution profile in phosphate buffers (pH 6.8 and pH 7.4). Computational investigations with molecular dynamics simulations also supported the formation of stable cocrystals. The drug release of APX from the tablets was considerably increased when compared with the pure APX in both pH conditions and it was found to increase with an increase in media pH. The present investigation represents an alternative approach for optimizing physicochemical and PK properties of Biopharmaceutical Classification System class-III drugs without changing its molecular structure and intrinsic bioactivities.

Enhanced Water Solubility and Oral Bioavailability of Paclitaxel Crystal Powders through an Innovative Antisolvent Precipitation Process: Antisolvent Crystallization Using Ionic Liquids as Solvent

Paclitaxel (PTX) is a poor water-soluble antineoplastic drug with significant antitumor activity. However, its low bioavailability is a major obstacle for its biomedical applications. Thus, this experiment is designed to prepare PTX crystal powders through an antisolvent precipitation process using 1-hexyl-3-methylimidazolium bromide (HMImBr) as solvent and water as an antisolvent. The factors influencing saturation solubility of PTX crystal powders in water in water were optimized using a single-factor design. The optimum conditions for the antisolvent precipitation process were as follows: 50 mg/mL concentration of the PTX solution, 25 °C temperature, and 1:7 solvent-to-antisolvent ratio. The PTX crystal powders were characterized via scanning electron microscopy, Fourier transform infrared spectroscopy, high-performance liquid chromatography–mass spectrometry, X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, Raman spectroscopy, solid-state nuclear magnetic resonance, and dissolution and oral bioavailability studies. Results showed that the chemical structure of PTX crystal powders were unchanged; however, precipitation of the crystalline structure changed. The dissolution test showed that the dissolution rate and solubility of PTX crystal powders were nearly 3.21-folds higher compared to raw PTX in water, and 1.27 times higher in artificial gastric juice. Meanwhile, the bioavailability of PTX crystal increased 10.88 times than raw PTX. These results suggested that PTX crystal powders might have potential value to become a new oral PTX formulation with high bioavailability.

Polymorphs of DP-VPA Solid Solutions and Their Physicochemical Properties

Different solid forms possess various physicochemical properties, which can significantly affect the stability, bioavailability, and manufacturability of the final product. DP-VPA, a complex of 1-stearoyl-2-valproyl-sn-glycero-3-phosphatidylcholine (DP-VPA-C₁₈) and 1-palmitoyl-2-valproyl-sn-glycero-3-phosphatidylcholine (DP-VPA-C₁₆), is currently under development as an antiepileptic drug. DP-VPA-C₁₆ and DP-VPA-C₁₈ crystallize together in solid solution forms. The solid forms of DP-VPA solid solution were studied herein. Powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), dynamic vapor sorption (DVS) and optical microscopy were used to characterize the different crystalline forms, known as polymorphs. The physicochemical properties, including hygroscopicity, thermodynamic behavior, and relative stability, of each form were investigated. DVS analysis showed that DP-VPA solid solution reduced the hygroscopicity of DP-VPA-C₁₆. The relative humidity stability study revealed that Forms A and B are relatively stable, while Forms A-1, B-1, C and D are highly unstable under natural humidity. Further analysis revealed that Form A transforms into Form B through milling. Given the physicochemical properties of the available physical forms, Form B may be the optimal form for the formulation and development of antiepileptic drugs.

Improving Dissolution and Cytotoxicity by Forming Multidrug Crystals

Both rosiglitazone and metformin have effects on blood glucose regulation and the proliferation of liver cancer cells. Combination therapy with these two drugs is common and effective for the treatment of diabetes in the clinic, however, the application of these two drugs is influenced by the poor dissolution of rosiglitazone and the gastrointestinal side-effect of metformin resulting from a high solubility. The formation of a multidrug crystal form (Rsg-Met) by a solvent evaporation method can solve the solubility issue. Crystal structure data and intramolecular hydrogen bonds were detected by X-ray diffraction and infrared spectroscopy. Surprisingly, Rsg-Met shortens the time spent in solubility equilibrium and multiplies the dissolution rate of Rsg. Finally, we found that a low concentration of Rsg-Met enhanced the proliferation inhibition effect on liver cancer cells (HepG2, SK-hep1) compared with rosiglitazone, without affecting the human normal cell line LO2.

Preparation of quercetin–nicotinamide cocrystals and their evaluation under in vivo and in vitro conditions

Quercetin is a flavonoid abundant in the plant kingdom. Various types of bioactivities of quercetin have been demonstrated in vitro. Although quercetin has been proposed to exhibit numerous pharmacological benefits, it suffers from low bioavailability on account of its obviously poor solubility in water. Cocrystals have generated interest recently as a way of enhancing the dissolution in vitro and creating relative bioavailability of insoluble medicine. In this study, quercetin–nicotinamide cocrystals were obtained via a solvent evaporation technique. Furthermore, quercetin–nicotinamide cocrystals were characterized via Fourier transform infrared (FI-IR) spectroscopy, X-ray powder diffraction (PXRD), and differential scanning calorimetry (DSC) techniques. Quercetin–nicotinamide cocrystals are a new phase material, and the established intermolecular forces such as hydrogen bonds between quercetin and nicotinamide existed in the quercetin–nicotinamide cocrystals, as confirmed from the solid-state analysis. The dissolution of quercetin–nicotinamide cocrystals was found to be significantly higher than that of quercetin crystals. The pharmacokinetic data from the in vivo experiments suggested that quercetin–nicotinamide cocrystals could significantly increase the oral absorption of quercetin by nearly 4-fold. These results demonstrate that the developed quercetin–nicotinamide cocrystals are a promising oral formulation toward improvement in the dissolution and bioavailability of quercetin.

Quercetin is a flavonoid abundant in the plant kingdom.

Enhancing the solubility of natural compound xanthotoxin by modulating stability via cocrystallization engineering

A comprehensive cocrystal study for the insoluble natural pharmaceutical compound xanthotoxin (XT) was conducted, in which xanthotoxin-para aminobenzoic acid (XT-PABA) and xanthotoxin-oxalic acid (XT-OA) cocrystals were obtained. The xanthotoxin cocrystals were characterized by powder X-ray diffraction, thermal analysis, and FT-IR spectra, and the crystal structures were determined by single-crystal X-ray diffraction. Crystal structures and thermal analysis showed that XT-OA was more stable than XT-PABA. Energy framework calculation indicated that H-bond and π···π interactions generated in XT-OA were stronger than that in XT-PABA and xanthotoxin. The powder dissolution experiments of xanthotoxin and its cocrystals suggested the XT-OA cocrystal might be applied as an alternative formulation of API, on account of its enhanced solubility and stability in the hydrochloric acid buffer solution (pH 1.2). The cocrystallization engineering can prolong the enhanced apparent solubility via modulating the stability.

Engineering Cocrystals of PoorlyWater-Soluble Drugs to Enhance Dissolution in Aqueous Medium

Biopharmaceutics Classification System (BCS) Class II and IV drugs suffer from poor aqueous solubility and hence low bioavailability. Most of these drugs are hydrophobic and cannot be developed into a pharmaceutical formulation due to their poor aqueous solubility. One of the ways to enhance the aqueous solubility of poorlywater-soluble drugs is to use the principles of crystal engineering to formulate cocrystals of these molecules with water-soluble molecules (which are generally called coformers). Many researchers have shown that the cocrystals significantly enhance the aqueous solubility of poorly water-soluble drugs. In this review, we present a consolidated account of reports available in the literature related to the cocrystallization of poorly water-soluble drugs. The current practice to formulate new drug cocrystals with enhanced solubility involves a lot of empiricism. Therefore, in this work, attempts have been made to understand a general framework involved in successful (and unsuccessful) cocrystallization events which can yield different solid forms such as cocrystals, cocrystal polymorphs, cocrystal hydrates/solvates, salts, coamorphous solids, eutectics and solid solutions. The rationale behind screening suitable coformers for cocrystallization has been explained based on the rules of five i.e., hydrogen bonding, halogen bonding (and in general non-covalent bonding), length of carbon chain, molecular recognition points and coformer aqueous solubility. Different techniques to screen coformers for effective cocrystallization and methods to synthesize cocrystals have been discussed. Recent advances in technologies for continuous and solvent-free production of cocrystals have also been discussed. Furthermore, mechanisms involved in solubilization of these solid forms and the parameters influencing dissolution and stability of specific solid forms have been discussed. Overall, this review provides a consolidated account of the rationale for design of cocrystals, past efforts, recent developments and future perspectives for cocrystallization research which will be extremely useful for researchers working in pharmaceutical formulation development.

Cryochemically Obtained Nanoforms of Antimicrobial Drug Substance Dioxidine and Their Physico-chemical and Structural Properties

Nanoforms of the antimicrobial drug substance 2,3-bis-(hydroxymethyl) quinoxaline-N,N′-dioxide with particles sizes between 50 and 300 nm were obtained by cryochemical modification of the initial pharmaceutical substance using a freeze-drying technique and were characterized by different physicochemical methods (FTIR, UV-Vis, 1H-NMR, DSC, TG and X-ray diffraction) and transmission electron microscopy (TEM). The data obtained from FTIR- and UV–Vis-spectroscopy confirmed the unaltered chemical structure of dioxidine molecules due to the cryochemical modification method. At the same time, X-ray diffraction and thermal analysis data show the change of the crystal structure compared to the parameters of the initial pharmaceutical dioxidine substance. A higher dissolution rate was revealed for cryomodified dioxidine nanoforms. The existence of three polymorphic crystal phases was established for cryomodified dioxidine samples possessed by some thermal activation processes: two anhydrous polymorphic phases, triclinic (T) and monoclinic (M), and one hydrated form (H).

Pharmaceutical cocrystallization techniques. Advances and challenges

Cocrystals are homogenous (single-phase) crystalline structures composed by two or more components in a definite stoichiometric ratio bonded together by noncovalent bonds. Pharmaceutical industry has been showing interest in cocrystals due to their ability to improve active pharmaceutical ingredients (API's) properties, such as solubility, dissolution, bioavailability, stability and processability. The necessity for high-throughput screening methods and methods capable of producing cocrystals in an industrial scale still hinders the use of cocrystals by the pharmaceutical industry. The aim of this review is to present an extensive overview of the cocrystallization methods, focusing in the specificities of each technique, its advantages and disadvantages. The review is divided into solvent-based and solvent-free methods. The most appropriate methods to the different stages of cocrystals manufacture, from the screening phase to industrial production are identified. The use of continuous and scalable methods in cocrystal production as well as the implementation of quality-by-design and process analytical technology concepts are also addressed.

Experimental cocrystal screening and solution based scale-up cocrystallization methods

Cocrystals are crystalline single phase materials composed of two or more different molecular and/or ionic compounds generally in a stoichiometric ratio which are neither solvates nor simple salts. If one of the components is an active pharmaceutical ingredient (API), the term pharmaceutical cocrystal is often used. There is a growing interest among drug development scientists in exploring cocrystals, as means to address physicochemical, biopharmaceutical and mechanical properties and expand solid form diversity of the API. Conventionally, coformers are selected based on crystal engineering principles, and the equimolar mixtures of API and coformers are subjected to solution-based crystallization that are commonly employed in polymorph and salt screening. However, the availability of new knowledge on cocrystal phase behaviour in solid state and solutions has spurred the development and implementation of more rational experimental cocrystal screening as well as scale-up methods. This review aims to provide overview of commonly employed solid form screening techniques in drug development with an emphasis on cocrystal screening methodologies. The latest developments in understanding and the use of cocrystal phase diagrams in both screening and solution based scale-up methods are also presented. Final section is devoted to reviewing the state of the art research covering solution based scale-up cocrystallization process for different cocrystals besides more recent continuous crystallization methods.

Crystal Structure Analysis of the First Discovered Stability-Enhanced Solid State of Tenofovir Disoproxil Free Base Using Single Crystal X-ray Diffraction

Tenofovir disoproxil (TD), an anti-virus drug, is currently marketed under its most stable form, Form-I of Tenofovir disoproxil fumarate (TDF). However, studies regarding the properties of TD free base crystal as a promising drug as well as its crystal structure have not yet been reported. This assumption was made because TD free base is not directly produced in a solid form during the manufacturing process. TD free base is first obtained in an oil form, and is then synthesized into TDF crystal. In this regard, the present study was conducted to investigate both the potentiality of TD free base to be an active pharmaceutical ingredient (API) and its crystal structure. Here, TD free base solid was produced by means of drowning-out crystallization. Next, single crystal X-ray diffraction (SXD) was employed to determine the crystal structure. Powder X-ray diffraction (PXRD) and a differential scanning calorimetry (DSC) analysis were performed to evaluate the crystal’s properties. Furthermore, experiments were carried out at 15%, 35%, 55%, 75%, and 95% relative humidity (RH) for 12 h using a hygroscopic tester to determine and to compare the hygroscopicity and stability of TD free base with TDF crystal. Additionally, experiments were conducted under accelerated (40 °C, RH 75%) and stress storage (60 °C, RH 75%) conditions for 30 days to investigate the changes in purity and the formation of dimer. In this work, we report that TD free base possesses lower hygroscopicity, and thus does not generate dimer impurity from hydrolysis. Primarily, this is attributed to the fact that TD free base is not an easily ionized salt but comprises neutral hydrophobic molecules. According to the structural properties, the improved hygroscopic property of the TD free base crystal was due to the decrease of crystal polarity owing to the intermolecular H-bonds present in TD free base rings. In addition, the solubility investigation study carried out in aqueous solution and at gastrointestinal pH revealed a similarity in TDF and TD free base solubility under the mentioned conditions. Accordingly, we could confirm the potentiality of TD free base as an active pharmaceutical ingredient.

Is Failure of Cocrystallization Actually a Failure? Eutectic Formation in Cocrystal Screening of Hesperetin

Cocrystal screening of hesperetin with certain countermolecules generated highly soluble noncovalent derivatives in the form of eutectics, instead of expected cocrystals. As adhesive forces established by complimentary functional groups on hesperetin and coformers were unable to overcome the stress due to size shape mismatch of component molecules, thus, eutectics were formed. Hesperetin, a polyphenolic antioxidant with potent anticancer and cardioprotective effects, has an underdeveloped role in modern therapeutics on account of its critically low aqueous solubility resulting in stunted bioavailability. The liquid-assisted cogrinding of hesperetin and coformers generated binary-phase eutectics in fixed stoichiometry with theophylline (1:1.5), adenine (2:1), gallic acid (1.5:1), and theobromine (2:1). Primarily characterized by lower melting endotherm in differential scanning calorimetry, the eutectics showed complete melting in hot-stage microscopy. Apart from characteristic V-shaped binary-phase diagram, no discernible changes in the FTIR and powder X-ray diffraction spectra further confirm eutectic formation. The morphological differences were analyzed by SEM measurements. A 2 to 4 times enhanced dissolution profile of the eutectics measured in pH 7.4 aqueous buffer was coupled with the in vitro (1,1-diphenyl-2-picryl hydroxyl free radical antioxidant assay and RBC antihemolytic assay) studies to present a complete preliminary data on the improved bioavailability of hesperetin eutectics.

Solubility and in vitro drug permeation behavior of ethenzamide cocrystals regulated in physiological pH environments

Drug release behavior of few ethenzamide cocrystals was investigated at different pH buffers. Change in lipophilic behavior and conformational adjustment of drug along with supramolecular synthons were probed for their improved drug efficacy.

A new polymorphic form and polymorphic transformation of loratadine

In this work, a new form of loratadine (Form B) was prepared from a 20% methanol and 80% water mixture and characterized by polarizing microscopy, scanning electron microscopy, powder X-ray diffraction and differential scanning calorimetry.

Synthesis, structure determination, and formation of a theobromine : oxalic acid 2 : 1 cocrystal

The structure and the formation pathway of a new theobromine : oxalic acid (2 : 1) cocrystal are presented.

The role of a liquid in “dry” co-grinding: a case study of the effect of water on mechanochemical synthesis in a “l-serine–oxalic acid” system

[l-serH]₂[ox]·2H₂O form II proved to be an intermediate product in the reaction for obtaining the form I.

Evaluation of the formation pathways of cocrystal polymorphs in liquid-assisted syntheses

Small but important: the kind of solvent added in liquid-assisted grinding syntheses of cocrystals influences the final product and the reaction rate.

Hydrogen bond synthon competition in the stabilization of theophylline cocrystals

In the preparation of theophylline cocrystals, phenol coformers facilitate water assimilation due to their weaker O–H⋯N(imidazole) synthon. The presence of –COOH prevents water incorporation and provides added physical stability at high humidity. This study shows the feasibility of cocrystal design of an API to tune physical properties based on hydrogen bond synthons.

Systemic exposure, tissue distribution, and disease evolution of a high solubility ciprofloxacin-aluminum complex in a murine model of septicemia induced by salmonella enterica serotype Enteritidis

A new pharmaceutical derivative obtained by stoichiometric complexation of ciprofloxacin (CIP) with aluminum (CIP-complex) has been investigated and reported in this study. Such product has high solubility in the gastrointestinal pH range and was successful in the development of optimized formulations while maintaining its antimicrobial potency. The systemic exposure, tissue distribution, and the disease evolution after given CIP-complex were assessed. The systemic exposure and distribution in intestines, lungs, and kidneys after a single intragastric administration of CIP-complex and CIP given alone, used as reference, were performed in Balb-C mice at a dose of 5 mg CIP/kg. For the assessment of the disease evolution assay, mice were infected with a virulent strain of Salmonella enterica serotype Enteritidis and treated intragastrically once or twice daily during 5 consecutive days with solutions of CIP-complex or the reference. Clinical follow up and survival was measured during 15 days post inoculation and health state was scored during this period from 0 to 5. CIP-complex showed a 32% increase in C(max), an earlier T(max), and a smaller AUC(0-12) than the reference. Maximum tissue concentrations (0.5-1 h) were significantly higher in CIP-complex (447% in intestine, 93% in kidney, and 44% in lungs). In the infection model used in this study, survival in CIP-complex versus CIP groups was 40% versus 20% (twice-daily administration) and 30% versus 0% (once-daily administration). Health state of the survivors of CIP-complex group (5/5) was higher than CIP group (3/5). The greater effectiveness of CIP-complex is attributed to the higher levels of CIP in the intestine. Our results supported the fact that CIP-complex is a promising candidate to develop dose-efficient formulations of CIP for oral administration.

4-[3-(Pyridin-4-yl)prop-yl]pyridinium 2-carb-oxy-benzoate

In the title molecular salt, C₁₃H₁₅N₂⁺·C₈H₅O₄⁻, the 2-carb­oxy­benzoate anions are joined into a chain along [010] by strong O—H⋯O hydrogen bonds, with the H atoms disordered about the inter­vening centres of inversion. The presence of N—H⋯O hydrogen bonds between cations generates an additional chain along [010] and parallel to that of the anions. The chains are assembled into a three-dimensional framework via weak C—H⋯O inter­chain inter­actions. In the cation, thee dihedral angle between the pyridine rings is 48.91 (4)°.

Polymorphic and kinetic investigation of adefovir dipivoxil during phase transformation

To search polymorphs of adefovir dipivoxil (AD), the polymorphic transformation approach in solution was developed. Also, the kinetics of polymorphic transformation was investigated to effectively control polymorphs. The AD crystals were obtained by crystallization at -10°C, and then the polymorphic transformation was induced by raising temperature. The polymorphs of AD were confirmed using DSC, XRD and solubility analyses. The polymorphic fraction during transformation was monitored for kinetic investigation. Via polymorphic transformation in solution, four polymorphs of AD were found and two of them were new (NF-I, NF-II). The DSC analysis revealed that solvate form (NF-I) was changed to form-V in solid state, and then re-crystallized to NF-II at 93°C, and finally became form-I at 97°C. This serial change of polymorphs in DSC was identical to polymorphic transformation sequence in solution. The kinetic rates of polymorphic transformation described by nucleation and mass transfer theories were well matched with experimental measurement. The polymorphic transformation approach was effective to search polymorphs of which the structure was changed to the other one in the solution. The kinetic information of polymorphic transformation predicted by Volmer's nucleation model and Stokes-Einstein diffusion equation was valuable for exact control of polymorphic purity.

Cocrystals of quercetin with improved solubility and oral bioavailability

Flavonoids have been studied extensively due to the observation that diets rich in these compounds are associated with lower incidences of many diseases. One of the most studied flavonoids, quercetin, is also the most abundant of these compounds in the plant kingdom. Numerous therapeutic bioactivities have been identified in vitro. However, its in vivo efficacy in pure form is limited by poor bioavailability, primarily due to its low solubility and consequent low absorption in the gut. Cocrystallization has gained attention recently as a means for improving the physicochemical characteristics of a compound. Here, we synthesized and evaluated four new cocrystals of quercetin (QUE): quercetin:caffeine (QUECAF), quercetin:caffeine:methanol (QUECAF·MeOH), quercetin:isonicotinamide (QUEINM), and quercetin:theobromine dihydrate (QUETBR · 2H(2)O). Each of these cocrystals exhibited pharmacokinetic properties that are vastly superior to those of quercetin alone. Cocrystallization was able to overcome the water insolubility of quercetin, with all four cocrystals exhibiting some degree of solubility. The QUECAF and QUECAF·MeOH cocrystals increased the solubility of QUE by 14- and 8-fold when compared to QUE dihydrate. We hypothesized that this improved solubility would translate into enhanced systemic absorption of QUE. This hypothesis was supported in our pharmacokinetic study. The cocrystals outperformed QUE dihydrate with increases in bioavailability up to nearly 10-fold.