New forms of old drugs: improving without changing

Salt or Cocrystal Puzzle Solved by Mechanochemistry: The Role of Solvent in the Pamoic Acid Case Study

Many drugs are nowadays marketed as salts. Cocrystallization is also emerging as a convenient tool to modify in vivo activity of pharmacologically active compounds. Given the marked difference in physicochemical properties between salts and cocrystals, the possibility of obtaining crystalline systems composed of the same building blocks in their neutral or charged form is desirable. Pamoic acid (PAM) is widely used in pharmaceutical formulation as pamoate salt, and we here propose a unique synthetic strategy to obtain a cocrystal of PAM rather than a salt by tuning mechanochemical conditions. Our findings have been corroborated by means of computational analyses, relating to the noncovalent interactions in the crystal structure with the formation of the different crystalline forms. A detailed analysis of the structure containing PAM in its neutral, anionic or dianionic form present in the Cambridge Structural Database (CSD) helped generalizing our results.

A new ciprofibrate calcium salt with improved solubility and intrinsic dissolution rate

Ciprofibrate (CIP) is an active pharmaceutical ingredient (API) classified as class II on the basis of biopharmaceutical classification system (BCS), what indicates that it has low solubility in aqueous solvents. The use of API salts has attracted attention due to their improvements in solubility, tolerability, higher rate and extent of absorption, and faster onset of the therapeutic effect. In this work, a new crystalline CIP monohydrated calcium salt (Ca(CIP)2.H2O) was successfully obtained and its crystal structure determined by single crystal X-ray diffraction analysis (SCXRD). Additionally, Ca(CIP)2.H2O was widely characterized by powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and submitted to solubility, intrinsic dissolution and accelerated stability studies. Ca(CIP)2.H2O exhibited higher solubility and dissolution rate than CIP-free form and was stable up to 6 months at 40 °C (75 %RH). Therefore, Ca(CIP)2.H2O may be a viable alternative for use in solid dosage forms.

Review of Personalized Medicine and Pharmacogenomics of Anti-Cancer Compounds and Natural Products

In recent years, the FDA has approved numerous anti-cancer drugs that are mutation-based for clinical use. These drugs have improved the precision of treatment and reduced adverse effects and side effects. Personalized therapy is a prominent and hot topic of current medicine and also represents the future direction of development. With the continuous advancements in gene sequencing and high-throughput screening, research and development strategies for personalized clinical drugs have developed rapidly. This review elaborates the recent personalized treatment strategies, which include artificial intelligence, multi-omics analysis, chemical proteomics, and computation-aided drug design. These technologies rely on the molecular classification of diseases, the global signaling network within organisms, and new models for all targets, which significantly support the development of personalized medicine. Meanwhile, we summarize chemical drugs, such as lorlatinib, osimertinib, and other natural products, that deliver personalized therapeutic effects based on genetic mutations. This review also highlights potential challenges in interpreting genetic mutations and combining drugs, while providing new ideas for the development of personalized medicine and pharmacogenomics in cancer study.

Never-Ending Story: New Cyclodextrin-Based Metal-Organic Framework Crystal Structures Obtained Using Different Crystallization Methods

Six novel cyclodextrin (CD)-based metal-organic frameworks (MOFs) were synthesized using distinct crystallization methodologies. A modified vapor diffusion method is introduced for the first time, termed fast crystallization, which enables the rapid solid-state formation of MOF compounds. This innovative method yielded four of the newly synthesized MOFs. The crystal structures of five obtained frameworks were structurally characterized through single-crystal X-ray diffraction, while one, compound 5 (γ-CD-K-5), was additionally characterized as a bulk powder. Structural analysis revealed that two of the newly obtained MOFs, namely, compound 2 (α-CD-K-2) and compound 3 (α-CD-Rb-3), exhibited isostructural characteristics, forming a three-dimensional (3D) framework. Compound 1 (α-CD-K-1) shared the same space group as EVEGET (α-CD-K) and displayed the same framework type. Furthermore, the crystal packing of compound 4 (β-CD-K-4) closely resembled that of compound 1 and EVEGET, with the only distinction lying in the type of CD employed. Notably, compound 6 (γ-CD-K-6) incorporated an iodine ion with an occupancy of 0.2. To discern the intermolecular interactions within the obtained MOFs, the Hirshfeld surface was calculated using Crystal Explorer software.

Unveiling polyamorphism and polyamorphic interconversions in pharmaceuticals: the peculiar case of hydrochlorothiazide

Polyamorphism has been a controversial and highly debated solid-state phenomenon in both material and pharmaceutical communities. Although some evidence of this fascinating phenomenon has been reported for several inorganic systems, and more recently also for a few organic compounds, the occurrence of polyamorphism is poorly understood and the molecular-level organization of polyamorphic forms is still unknown. Here we have investigated the occurrence of polyamorphism and polyamorphic interconversions in hydrochlorothiazide (HCT), using both experimental and computational methods. Three distinct HCT polyamorphs, presenting distinct physical and thermal stabilities as well as distinct relaxation properties, were systematically prepared using spray-drying (SD), quench-cooling (QC) and ball milling (BM) methods. HCT polyamorph II (obtained by QC) was found to be more physically stable than polyamorphs I and III (obtained by SD and BM, respectively). Furthermore, polyamorphs I and III could be converted into polyamorph II after QC, while polyamorph II did not convert to any other polyamorph after SD or BM. Molecular dynamics simulations show that HCT dihedral angle distributions are significantly different for polyamorphs I and II, which is postulated as a possible explanation for their different physicochemical properties.

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.

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.

Pharmaceutical Salts of Piroxicam and Meloxicam with Organic Counterions

Piroxicam (PRM) and meloxicam (MEL) are two nonsteroidal anti-inflammatory drugs, belonging to the Biopharmaceutics Classification System Class II drugs. In this study, six novel pharmaceutical salts of PRM and MEL with three basic organic counterions, that is, 4-aminopyridine (4AP), 4-dimethylaminopyridine (4DMP), and piperazine (PPZ), were prepared by both slurrying and slow evaporation. These salts were characterized by single-crystal and powder X-ray diffraction, thermal analysis, and Fourier transform infrared spectroscopy. All six salts, especially MEL-4DMP and MEL-4AP, showed a significantly improved apparent solubility and dissolution rate in sodium phosphate solution compared with the pure APIs. Notably, PRM-4AP and PRM-4DMP salts exhibited enhanced fluorescence, and the PRM-PPZ salt showed weaker fluorescence compared with that of pure PRM due to different luminescence mechanisms.

Impact of the Dicarboxylic Acid Chain Length on Intermolecular Interactions with Lidocaine

Acid-base multicomponent systems have become a popular choice as a strategy to fine-tune the physicochemical properties of active pharmaceutical ingredients. Current prediction tools based on the principles of anticrystal engineering cannot always accurately predict the nature of intermolecular interactions within a multicomponent system. Even small changes in the physicochemical parameters of parent components can result in unexpected outcomes, and many salt, cocrystal, and ionic liquid forms are still being discovered empirically. In this work, we aimed to establish structural consistency in a series of mixtures comprising lidocaine (LID) with decanedioic, undecanedioic, dodecanedioic, and tridecanedioic acids and to explore how length and flexibility of the acid carbon backbone affect the molecular recognition, crystallization, and thermal behavior of the expected binary systems. We found that neat grinding of LID with dicarboxylic acids results in the formation of eutectic phases. The observed eutectic melting points deviated from the ideal eutectic temperatures predicted by the Schroeder van Laar model because of hydrogen bonding between the reacting components within the mixtures. Furthermore, thermal and infrared analysis provided evidence for the possible formation of new phases stemming from partial ionization of the counterions. Besides, the structure of a previously undetermined form I of the tridecanedioic acid was solved by single crystal X-ray diffraction.

Active pharmaceutical ingredients (APIs) in ionic liquids: An effective approach for API physiochemical parameter optimization

Ionic liquids (ILs) are widely used as solvents, co-solvents and permeation enhancers in the biomedical and pharmaceutical fields. There are many advantages to using active pharmaceutical ingredients (APIs) in the production of ILs for drug delivery, including the ability to tailor solubility, improve thermal stability, increase dissolution, regulate drug release, improve API permeability, and modulate cytotoxicity on tumor cells. Such an approach has shown significant potential as a tool for drug delivery. As a result, APIs converted into ILs are used as active components in solutions, emulsions, and even nanoparticles (NPs). In this review, we explore the use and physiochemical characteristics of APIs via ILs, including improvements of their physicochemical properties in preformulation and formulation development.

NMR study of the inclusion complexes of β-cyclodextrin with diphenhydramine, clonidine and tolperisone

Abstract

Forming complexes with β-cyclodextrin can enhance stability, dissolution rate, solubility, and bioavailability of an active pharmaceutical ingredient. In this study, the inclusion behavior between β-cyclodextrin (β-CD) and diphenhydramine, clonidine, and tolperisone in DMSO-d6 was investigated using NMR spectroscopy. 1H, 13C, COSY, HMQC, and ROESY data were applied to determine the structure of inclusion complexes, and molecular docking analysis was engaged to identify the most favorable host–guest interactions in the inclusion complexes. Complexation of β-CD with diphenhydramine, clonidine, and tolperisone is accompanied by the insertion of a molecular fragment of the guest molecule, one molecule of diphenhydramine and tolperisone, and two molecules of clonidine, into the inner sphere of one host molecule. The reported study provides useful information for the potential application of the complexation of β-CD with diphenhydramine, clonidine, and tolperisone. This may be a good strategy for the development of solid pharmaceutical dosage forms based on β-CDs as a drug delivery system.

Article highlights

Solid-State Study of the Structure, Dynamics, and Thermal Processes of Safinamide Mesylate─A New Generation Drug for the Treatment of Neurodegenerative Diseases

Safinamide mesylate (SM), the pure active pharmaceutical ingredient (API) recently used in Parkinson disease treatment, recrystallized employing water–ethanol mixture of solvents (vol/vol 1:9) gives a different crystallographic form compared to SM in Xadago tablets. Pure SM crystallizes as a hemihydrate in the monoclinic system with the P2₁ space group. Its crystal and molecular structure were determined by means of cryo X-ray crystallography at 100 K. SM in the Xadago tablet exists in anhydrous form in the orthorhombic crystallographic system with the P2₁2₁2₁ space group. The water migration and thermal processes in the crystal lattice were monitored by solid-state NMR spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. SM in Xadago in the high-humidity environment undergoes phase transformation to the P2₁ form which can be easily reversed just by heating up to 80 °C. For the commercial form of the API, there is also a reversible thermal transformation observed between Z′ = 1 ↔ Z′ = 3 crystallographic forms in the 0–20 °C temperature range. Analysis of molecular motion in the crystal lattice proves that the observed conformational polymorphism is forced by intramolecular dynamics. All above-mentioned processes were analyzed and described employing the NMR crystallography approach with the support of advanced theoretical calculations.

Two Crystal Forms of a Hydrated 2:1 β-Cyclodextrin Fluconazole Complex: Single Crystal X-ray Structures, Dehydration Profiles, and Conditions for Their Individual Isolation

Inclusion complexes between cyclodextrins (CDs) and active pharmaceutical ingredients (APIs) have potential for pharmaceutical formulation. Since crystallization of a given complex may result in the isolation of multiple crystal forms, it is essential to characterize these forms with respect to their structures and physicochemical properties to optimize pharmaceutical candidate selection. Here, we report the preparation and characterization of two crystallographically distinct hydrated forms of an inclusion complex between β-cyclodextrin (β-CD) and the antifungal API fluconazole (FLU) as well as temperature–concentration conditions required for their individual isolation. Determination of crystal water contents was achieved using thermoanalytical methods. X-ray analyses revealed distinct structural differences between the triclinic (TBCDFLU, space group P1) and monoclinic (MBCDFLU, space group C2) crystal forms. Removal of the crystals from their mother liquors led to rapid dehydration of the MBCDFLU crystal, while the TBCDFLU crystal was stable, a result that could be reconciled with the distinct packing arrangements in the respective crystals. This study highlights (a) the importance of identifying possible multiple forms of a cyclodextrin API complex and controlling the crystallization conditions, and (b) the need to characterize such crystal forms to determine the extent to which their physicochemical properties may differ.

Anti-inflammatory and antioxidant effects of nanoformulations composed of metal-organic frameworks delivering rutin and/or piperine natural agents

Plant-derived natural medicines have been extensively studied for anti-inflammatory or antioxidant properties, but challenges to their clinical use include low bioavailability, poor solubility in water, and difficult-to-control release kinetics. Nanomedicine may offer innovative solutions that can enhance the therapeutic activity and control release kinetics of these agents, opening the way to translating them into the clinic. Two agents of particular interest are rutin (Ru), a flavonoid, and piperine (Pip), an alkaloid, which exhibit a range of pharmacological activities that include antioxidant and anti-inflammatory effects. In this work, nanoformulations were developed consisting of two metal–organic frameworks (MOFs) with surface modifications, Ti-MOF and Zr-MOF, each of them loaded with Ru and/or Pip. Both MOFs and nanoformulations were characterized and evaluated in vivo for anti-inflammatory and antioxidant effects. Loadings of ∼17 wt.% for a single pro-drug and ∼27 wt.% for dual loading were achieved. The release patterns for Ru and or Pip followed two stages: a zero-order for the first 12-hour stage, and a second stage of stable sustained release. At pH 7.4, the release patterns best fit to zero-order and Korsmeyer–Peppas kinetic models. The nanoformulations had enhanced anti-inflammatory and antioxidant effects than any of their elements singly, and those with Ru or Pip alone showed stronger effects than those with both agents. Results of assays using a paw edema model, leukocyte migration, and plasma antioxidant capacity were in agreement. Our preliminary findings indicate that nanoformulations with these agents exert better anti-inflammatory and antioxidant effects than the agents in their free form.

Cryochemical Production of Drug Nanoforms: Particle Size and Crystal Phase Control of the Antibacterial Medication 2,3-Quinoxalinedimethanol-1,4-dioxide (Dioxidine)

Increasing the effectiveness of known, well-tested drugs is a promising low-cost alternative to the search for new drug molecular forms. Powerful approaches to solve this problem are (a) an active drug particle size reduction down to the nanoscale and (b) thermodynamically metastable but kinetically stable crystal modifications of drug acquisition. The combined cryochemical method has been used for size and structural modifications of the antibacterial drug 2,3-quinoxalinedimethanol-1,4-dioxide (dioxidine). The main stage of the proposed technique includes the formation of a molecular vapor of the drug substance, combined with a carrier gas (CO₂) flow, followed by a fast condensation of the drug substance and CO₂ molecules on a cooled-by-liquid nitrogen surface of preparative cryostate. It was established that the molecular chemical structure of the drug substance remained unchanged during cryochemical modification; however, it led to a significant decrease of the drug particles’ size down to nanosizes and changes in the crystal structures of the solid drug nanoforms obtained. Varying carrier gas (CO₂) flow led to changes in their solid phase composition. A higher dissolution rate and changes in antibacterial activity were demonstrated for cryomodified dioxidine samples in comparison to the properties of the initial pharmacopeia dioxidine.

Evaluation of metal-based antimicrobial compounds for the treatment of bacterial pathogens

Antimicrobial resistance (AMR) is one of the greatest global health challenges of modern times and its prevalence is rising worldwide. AMR within bacteria reduces the efficacy of antibiotics and increases both the morbidity and the mortality associated with bacterial infections. Despite this growing risk, few antibiotics with a novel mode of action are being produced, leading to a lack of antibiotics that can effectively treat bacterial infections with AMR. Metals have a history of antibacterial use but upon the discovery of antibiotics, often became overlooked as antibacterial agents. Meanwhile, metal-based complexes have been used as treatments for other diseases, such as the gold-containing drug auranofin, used to treat rheumatoid arthritis. Metal-based antibacterial compounds have novel modes of action that provide an advantage for the treatment of bacterial infections with resistance to conventional antibiotics. In this review, the antibacterial activity, mode of action, and potential for systemic use of a number of metal-based antibacterial complexes are discussed. The current limitations of these compounds are highlighted to determine if metal-based agents are a potential solution for the treatment of bacterial infections, especially those resistant to conventional antibiotics.

Exploratory Study on Lercanidipine Hydrochloride Polymorphism: pH-Dependent Solubility Behavior and Simulation of its Impact on Pharmacokinetics

This work describes an exploratory experimental and in silico study of the influence of polymorphism, particle size, and physiology on the pharmacokinetics of lercanidipine hydrochloride (LHC). Equilibrium and kinetic solubility studies were performed on LHC forms I and II, as a function of pH and buffer composition. GastroPlus® was used to evaluate the potential effect of solubility differences due to polymorphism, particle size, and physiological conditions, on the drug pharmacokinetics. The results indicated that solubilities of LHC polymorphs are strongly dependent on the composition and pH of the buffer media. The concentration ratio (C_I/C_II) is particularly large for chloride buffer (C_I/C_II = 3.3-3.9) and exhibits a slightly decreasing tendency with the pH increase for all other buffers. Based on solubility alone, a higher bioavailability of form I might be expected. However, exploratory PBPK simulations suggested that (i) under usual fasted (pH 1.3) and fed (pH 4.9) gastric conditions, the two polymorphs have similar bioavailability, regardless of the particle size; (ii) at high gastric pH in the fasted state (e.g., pH 3.0), the bioavailability of form II can be considerably lower than that of form I, unless the particle size is < 20 μm. This study demonstrates the importance of investigating the effect of the buffer nature when evaluating the solubility of ionizable polymorphic substances. It also showcases the benefits of using PBPK simulations, to assess the risk and pharmacokinetic relevance of different solubility and particle size between crystal forms, for diverse physiological conditions.

Improved Manufacturability and In Vivo Comparative Pharmacokinetics of Dapagliflozin Cocrystals in Beagle Dogs and Human Volunteers

Dapagliflozin (DAP), which improves glycemic control in patients with type 2 diabetes mellitus, has poor physical properties against heat and moisture, thus hindering its manufacturing potential. The superior physicochemical properties of a recently developed cocrystal of DAP and citric acid (DAP cocrystal) in comparison with those of DAP and Forxiga^®, a patented solvate form with propandiol monohydrate, were identified via structural analysis and moisture sorption isotherm. For the first time, the formulation, manufacturability, and in vivo bioavailability of DAP cocrystals were successfully investigated to develop oral dosage forms that substitute Forxiga^®. The intrinsic dissolution rate of DAP cocrystal was controlled by varying particle size distribution. Unlike the direct compression (DC), roller compaction (RC) was more preferable to obtain good flowability of dry granules for a continuous manufacturing system. The cocrystal structure was maintained throughout the stability assessment period. In Vitro dissolution pattern differences of the optimized DAP cocrystal tablet with RC and the reference tablet, Forxiga^® 10 mg, were pharmaceutically equivalent within 5% in four different media. Furthermore, comparative pharmacokinetic analysis confirmed that a 10 mg DAP cocrystal tablet with RC was bioequivalent to a 10 mg Forxiga^® tablet, as assessed in beagle dogs and human volunteers.

Molecular Crystal Forms of Antitubercular Ethionamide with Dicarboxylic Acids: Solid-State Properties and a Combined Structural and Spectroscopic Study

We report on the preparation, characterization, and bioavailability properties of three new crystal forms of ethionamide, an antitubercular agent used in the treatment of drug-resistant tuberculosis. The new adducts were obtained by combining the active pharmaceutical ingredient with three dicarboxylic acids, namely glutaric, malonic and tartaric acid, in equimolar ratios. Crystal structures were obtained for all three adducts and were compared with two previously reported multicomponent systems of ethionamide with maleic and fumaric acid. The ethionamide-glutaric acid and the ethionamide-malonic acid adducts were thoroughly characterized by means of solid-state NMR (13C and 15N Cross-Polarization Magic Angle Spinning or CPMAS) to confirm the position of the carboxylic proton, and they were found to be a cocrystal and a salt, respectively; they were compared with two previously reported multicomponent systems of ethionamide with maleic and fumaric acid. Ethionamide-tartaric acid was found to be a rare example of kryptoracemic cocrystal. In vitro bioavailability enhancements up to a factor 3 compared to pure ethionamide were assessed for all obtained adducts.

Bioinspired Ion Pairs Transforming Papaverine into a Protic Ionic Liquid and Salts

Microbial, mammalian, and plant cells produce and contain secondary metabolites, which typically are soluble in water to prevent cell damage by crystallization. The formation of ion pairs, for example, with carboxylic acids or mineral acids, is a natural blueprint to maintain basic metabolites in solution. Here, we aim at showing whether the mostly large carboxylates form soluble protic ionic liquids (PILs) with the basic natural product papaverine resulting in enhanced aqueous solubility. The obtained PILs were characterized by 1H-15N HMBC nuclear magnetic resonance (NMR) and in the solid state using X-ray powder diffraction, differential scanning calorimetry, and dissolution measurements. Furthermore, their supramolecular pattern in aqueous solution was studied by means of potentiometric and photometrical solubility, NMR aggregation assay, dynamic light scattering, zeta potential, and viscosity measurements. Thereby, we identified the naturally occurring carboxylic acids, citric acid, malic acid, and tartaric acid, as being appropriate counterions for papaverine and which will facilitate the formation of PILs with their beneficial characteristics, like the improved dissolution rate and enhanced apparent solubility.

The Lisbon Supramolecular Green Story: Mechanochemistry towards New Forms of Pharmaceuticals

This short review presents and highlights the work performed by the Lisbon Group on the mechanochemical synthesis of active pharmaceutical ingredients (APIs) multicomponent compounds. Here, we show some of our most relevant contributions on the synthesis of supramolecular derivatives of well-known commercial used drugs and the corresponding improvement on their physicochemical properties. The study reflects, not only our pursuit of using crystal engineering principles for the search of supramolecular entities, but also our aim to correlate them with the desired properties. The work also covers our results on polymorphic screening and describes our proposed alternatives to induce and maintain specific polymorphic forms, and our approach to avoid polymorphism using APIs as ionic liquids. We want to stress that all the work was performed using mechanochemistry, a green advantageous synthetic technique.

Exploring solid forms of oxytetracycline hydrochloride

Oxytetracycline hydrochloride, an antibiotic of the tetracycline family, is a polymorphic drug that evidences erratic absorption in oral administration. Additionally, poor solid state characterization of the polymorphs and diversity in the existing nomenclature impede the correct identification of the raw materials. In this work, oxytetracycline hydrochloride solid forms were prepared from isopropyl alcohol, ethanol and methanol through different crystallization techniques, and then their physicochemical and microbiological properties were evaluated. A combination of advanced techniques such as solid state nuclear magnetic resonance, powder X-ray diffraction, infrared spectroscopy, thermal analysis, scanning electron microscopy and energy-dispersive X-ray spectroscopy were used in the characterization of solid samples giving clear evidence of the existence of three stable and one metastable solid forms of the oxytetracycline hydrochloride. Solubility was determined in aqueous solution, simulated gastric fluid, and simulated intestinal fluid. In addition, microbiological studies were performed. The polymorphs showed similar antimicrobial activity against Escherichia coli and Staphylococcus aureus. Therefore, these solid forms of oxytetracycline hydrochloride constitute promising candidates to encourage studies for repositioning old and known antibiotic drugs in the developing strategies for new therapeutic alternatives.

Optimization and comparison of statistical tools for the prediction of multicomponent forms of a molecule: the antiretroviral nevirapine as a case study

A methodology is proposed to assess the propensity to obtain multicomponent forms of an API based on the combination of modified statistical analytical tools to order the possible co-formers in a ranking index.

Plastically bendable pregabalin multi-component systems with improved tabletability and compressibility

Pregabalin (SPG) is brittle in nature without the presence of any slip planes. The coformer (OX/SA) facilitates the slip planes in order to make the brittle structure plastically bendable.

Insight into the Structure and Properties of Novel Imidazole-Based Salts of Salicylic Acid

The preparation of new active pharmaceutical ingredient (API) multicomponent crystal forms, especially co-crystals and salts, is being considered as a reliable strategy to improve API solubility and bioavailability. In this study, three novel imidazole-based salts of the poorly water-soluble salicylic acid (SA) are reported exhibiting a remarkable improvement in solubility and dissolution rate properties. All structures were solved by powder X-ray diffraction. Multiple complementary techniques were used to solve co-crystal/salt ambiguities: density functional theory calculations, Raman and ¹H/¹³C solid-state NMR spectroscopies. In all molecular salts, the crystal packing interactions are based on a common charged assisted ⁺N-H_(SA)⋯O⁻_(co-former) hydrogen bond interaction. The presence of an extra methyl group in different positions of the co-former, induced different supramolecular arrangements, yielding salts with different physicochemical properties. All salts present much higher solubility and dissolution rate than pure SA. The most promising results were obtained for the salts with imidazole and 1-methylimidazole co-formers.

Implication of Differential Surface Anisotropy on Biopharmaceutical Performance of Polymorphic Forms of Ambrisentan

The aim of the present study was to compare the dissolution rate and in vivo biopharmaceutical performance of 2 polymorphic forms (form I and II) of ambrisentan and correlate with their surface molecular environment. Dominance of various functionalities on the surface of specific crystal facets of both forms was predicted by Bravais-Friedel-Donnay-Harker method. Hirshfeld surface analysis maps and 2D fingerprint plots indicate a difference in shape index, curvedness, and relative percentage contribution of various contacts in both forms. Pre- and post-intrinsic dissolution compact studied by atomic force microscopy showed a significant difference in surface roughness and defects formation in form II as compared to form I which is attributed to the presence of more hydrophilic surfaces. The hydrophilic molecular surface environment of form II is ascribed to its improved intrinsic dissolution rate than form I. Furthermore, in vivo pharmacokinetic study also showed significantly higher AUC_0-24 and C_max in form II compared to form I. Overall, this study demonstrates that form I and II of ambrisentan exhibited the differential surface anisotropy which has significant implications on their biopharmaceutical performance.

Supramolecular assembly of two copper(II) coordination compounds of topiroxostat with dialkylformamide ligands

A well-known selective xanthine oxidase inhibitor topiroxostat, 4-[3-(4-pyridinyl)-1H-1,2,4-triazol-5-yl]-2-pyridinecarbonitrile (ptpc), was selected to react with Cu(NO3)2 · 3H2O in dialkylformamide solvents, affording two novel supramolecular coordination compounds [Cu(ptpc)2(NO3)(DMF)2] · NO3 (1) and Cu(ptpc)2(NO3)2(DEF)2 (2). Single-crystal X-ray diffraction revealed that compound 1 crystallizes in the monoclinic space group C2/c. The components are assembled to a 3D supramolecular framework through hydrogen-bonding interactions between the large [Cu(ptpc)2(NO3)(DMF)2]+ cationic moieties and the nitrate anions. Compound 2 crystallizes in the triclinic space group P1̅ and shows a 2D hydrogen-bonded network structure. The results clearly indicate that dialkylformamide solvents with different sizes have an important influence on the structures of the complexes. The luminescence properties of 1 and 2 in the solid state and their thermal stabilities were also investigated.

Multicomponent crystals of nitrofurazone – when more is less

Multicomponent crystal formation of nitrofurazone was challenging when the experimental work was based on popular crystal engineering principles.

Recent Trends in Covalent and Metal Organic Frameworks for Biomedical Applications

Materials science has seen a great deal of advancement and development. The discovery of new types of materials sparked the study of their properties followed by applications ranging from separation, catalysis, optoelectronics, sensing, drug delivery and biomedicine, and many other uses in different fields of science. Metal organic frameworks (MOFs) and covalent organic frameworks (COFs) are a relatively new type of materials with high surface areas and permanent porosity that show great promise for such applications. The current study aims at presenting the recent work achieved in COFs and MOFs for biomedical applications, and to examine some challenges and future directions which the field may take. The paper herein surveys their synthesis, and their use as Drug Delivery Systems (DDS), in non-drug delivery therapeutics and for biosensing and diagnostics.

Supercritical carbon dioxide-based technologies for the production of drug nanoparticles/nanocrystals - A comprehensive review

Low drug bioavailability, which is mostly a result of poor aqueous drug solubilities and of inadequate drug dissolution rates, is one of the most significant challenges that pharmaceutical companies are currently facing, since this may limit the therapeutic efficacy of marketed drugs, or even result in the discard of potential highly effective drug candidates during developmental stages. Two of the main approaches that have been implemented in recent years to overcome poor drug solubility/dissolution issues have frequently involved drug particle size reduction (i.e., micronization/nanonization) and/or the modification of some of the physicochemical and structural properties of poorly water soluble drugs. A large number of particle engineering methodologies have been developed, tested, and applied in the synthesis and control of particle size/particle-size distributions, crystallinities, and polymorphic purities of drug micro- and nano-particles/crystals. In recent years pharmaceutical processing using supercritical fluids (SCF), in general, and supercritical carbon dioxide (scCO₂), in particular, have attracted a great attention from the pharmaceutical industry. This is mostly due to the several well-known advantageous technical features of these processes, as well as to other increasingly important subjects for the pharmaceutical industry, namely their "green", sustainable, safe and "environmentally-friendly" intrinsic characteristics. In this work, it is presented a comprehensive state-of-the-art review on scCO₂-based processes focused on the formation and on the control of the physicochemical, structural and morphological properties of amorphous/crystalline pure drug nanoparticles. It is presented and discussed the most relevant scCO₂, scCO₂-based fluids and drug physicochemical properties that are pertinent for the development of successful pharmaceutical products, namely those that are critical in the selection of an adequate scCO₂-based method to produce pure drug nanoparticles/nanocrystals. scCO₂-based nanoparticle formation methodologies are classified in three main families, and in terms of the most important role played by scCO₂ in particle formation processes: as a solvent; as an antisolvent or a co-antisolvent; and as a "high mobility" additive (a solute, a co-solute, or a co-solvent). Specific particle formation methods belonging to each one of these families are presented, discussed and compared. Some selected amorphous/crystalline drug nanoparticles that were prepared by these methods are compiled and presented, namely those studied in the last 10-15 years. A special emphasis is given to the formation of drug cocrystals. It is also discussed the fundamental knowledge and the main mechanisms in which the scCO₂-based particle formation methods rely on, as well as the current status and urgent needs in terms of reliable experimental data and of robust modeling approaches. Other addressed and discussed topics include the currently available and the most adequate physicochemical, morphological and biological characterization methods required for pure drug nanoparticles/nanocrystals, some of the current nanometrology and regulatory issues associated to the use of these methods, as well as some scale-up, post-processing and pharmaceutical regulatory subjects related to the industrial implementation of these scCO₂-based processes. Finally, it is also discussed the current status of these techniques, as well as their future major perspectives and opportunities for industrial implementation in the upcoming years.

Towards medicinal mechanochemistry: evolution of milling from pharmaceutical solid form screening to the synthesis of active pharmaceutical ingredients (APIs)

This overview highlights the emergent area of mechanochemical reactions for making active pharmaceutical ingredients (APIs), and covers the latest advances in the recently established area of mechanochemical screening and synthesis of pharmaceutical solid forms, specifically polymorphs, cocrystals, salts and salt cocrystals. We also provide an overview of the most recent developments in pharmaceutical uses of mechanochemistry, including real-time reaction monitoring, techniques for polymorph control and approaches for continuous manufacture using twin screw extrusion, and more. Most importantly, we show how the overlap of previously unrelated areas of mechanochemical screening for API solid forms, organic synthesis by milling, and mechanochemical screening for molecular recognition, enables the emergence of a new research discipline in which different aspects of pharmaceutical and medicinal chemistry are addressed through mechanochemistry rather than through conventional solution-based routes. The emergence of such medicinal mechanochemistry is likely to have a strong impact on future pharmaceutical and medicinal chemistry, as it offers not only access to materials and reactivity that are sometimes difficult or even impossible to access from solution, but can also provide a general answer to the demands of the pharmaceutical industry for cleaner, safer and efficient synthetic solutions.

Pharmaceutical cocrystallization: an effective approach to modulate the physicochemical properties of solid-state drugs

This highlight presents an update on applications of cocrystallization to modify properties relevant to efficacy, safety, and manufacturability of drugs.

Mechanochemistryvs.solution growth: striking differences in bench stability of a cimetidine salt based on a synthetic method

A mechanochemically prepared solvated salt of an archetypal blockbuster drug exhibits significantly different bench stability to analogous material made in solution.

Comparison of the relative stability of pharmaceutical cocrystals consisting of paracetamol and dicarboxylic acids

OBJECTIVE

The aim of this study is to evaluate the relative stability of pharmaceutical cocrystals consisting of paracetamol (APAP) and oxalic acid (OXA) or maleic acid (MLA).

SIGNIFICANCE

These observations of cocrystal stability under various conditions are useful coformer criteria when cocrystals are selected as the active pharmaceutical ingredient in drug development.

METHOD

The relative stability was determined from the preferentially formed cocrystals under various conditions.

RESULT

Cocrystal of APAP-OXA was more stable than that of APAP-MLA in a ternary cogrinding system and possessed thermodynamical stability. On the other hand, when grinding with moisture or maintaining at high temperatures and relative humidity conditions, APAP-MLA was more stable, and OXA converted to OXA dihydrate. In the slurry method, APAP-OXA was more stable in aprotic solvents because the APAP-OXA with low-solubility product precipitated.

CONCLUSIONS

The relative stability order was affected by preparing conditions of presence of moisture. This order might attribute to the small difference of crystal structure in the extension of the hydrogen bond network.

Calcium Coordination Solids for pH-Triggered Release of Olsalazine

Calcium coordination solids were synthesized and evaluated for delivery of olsalazine (H₄ olz), an anti-inflammatory compound used for treatment of ulcerative colitis. The materials include one-dimensional Ca(H₂ olz)⋅4 H₂ O chains, two-dimensional Ca(H₂ olz)⋅2 H₂ O sheets, and a three-dimensional metal-organic framework Ca(H₂ olz)⋅2DMF (DMF=N,N-dimethylformamide). The framework undergoes structural changes in response to solvent, forming a dense Ca(H₂ olz) phase when exposed to aqueous HCl. The compounds Ca(H₂ olz)⋅x H₂ O (x=0, 2, 4) were each pressed into pellets and exposed to simulated gastrointestinal fluids to mimic the passage of a pill from the acidic stomach to the pH-neutral intestines. All three calcium materials exhibited a delayed release of olsalazine relative to Na₂ (H₂ olz), the commercial formulation, illustrating how formulation of a drug within an extended coordination solid can serve to tune its solubility and performance.

Pharmaceutical aspects of salt and cocrystal forms of APIs and characterization challenges

In recent years many efforts have been devoted to the screening and the study of new solid-state forms of old active pharmaceutical ingredients (APIs) with salification or co-crystallization processes, thus modulating final properties without changing the pharmacological nature. Salts, hydrates/solvates, and cocrystals are the common solid-state forms employed. They offer the intriguing possibility of exploring different pharmaceutical properties for a single API in the quest of enhancing the final drug product. New synthetic strategies and advanced characterization techniques have been recently proposed in this hot topic for pharmaceutical companies. This paper reviews the recent progresses in the field particularly focusing on the characterization challenges encountered when the nature of the solid-state form must be determined. The aim of this article is to offer the state-of-the-art on this subject in order to develop new insights and to promote cooperative efforts in the fascinating field of API salt and cocrystal forms.

Pharmaceutical Salts of Carvedilol: Polymorphism and Physicochemical Properties

We report novel pharmaceutical salts of an anti-hypertensive drug carvedilol (CVD) with pharmaceutically acceptable salt formers, including oxalic acid (OXA), fumaric acid (FUMA), benzoic acid (BZA), and mandelic acid (MDA) via conventional solvent evaporation technique. The pKa difference between CVD and selected acids was greater than 3, thus suggesting salt formation. Two polymorphic forms of CVD/MDA salts and one p-Dioxane solvate of CVD/FUMA salt were also reported in this paper. The salts were characterized by powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Stability of the salts was assessed by storage at 40°C/75% RH for 1 month. All CVD salts exhibited higher solubility in phosphate buffer solution pH 6.8 compared to the parent drug CVD and showed good stability in accelerated ICH conditions at 40°C/75% RH for 1 month. CVD/FUMA salt showed the highest solubility (1.78 times). Based on thermal analysis and slurry experiment, it was found that CVD/MDA polymorphs were related monotropically with Form 1 as the stable form. The results suggested that salt formation could be an alternative method to improve CVD solubility.

Biological Activity of Ionic Liquids and Their Application in Pharmaceutics and Medicine

Ionic liquids are remarkable chemical compounds, which find applications in many areas of modern science. Because of their highly tunable nature and exceptional properties, ionic liquids have become essential players in the fields of synthesis and catalysis, extraction, electrochemistry, analytics, biotechnology, etc. Apart from physical and chemical features of ionic liquids, their high biological activity has been attracting significant attention from biochemists, ecologists, and medical scientists. This Review is dedicated to biological activities of ionic liquids, with a special emphasis on their potential employment in pharmaceutics and medicine. The accumulated data on the biological activity of ionic liquids, including their antimicrobial and cytotoxic properties, are discussed in view of possible applications in drug synthesis and drug delivery systems. Dedicated attention is given to a novel active pharmaceutical ingredient-ionic liquid (API-IL) concept, which suggests using traditional drugs in the form of ionic liquid species. The main aim of this Review is to attract a broad audience of chemical, biological, and medical scientists to study advantages of ionic liquid pharmaceutics. Overall, the discussed data highlight the importance of the research direction defined as "Ioliomics", studies of ions in liquids in modern chemistry, biology, and medicine.

Advances in Solid-State Transformations of Coordination Bonds: From the Ball Mill to the Aging Chamber

Controlling the formation of coordination bonds is pivotal to the development of a plethora of functional metal-organic materials, ranging from coordination polymers, metal-organic frameworks (MOFs) to metallodrugs. The interest in and commercialization of such materials has created a need for more efficient, environmentally-friendly routes for making coordination bonds. Solid-state coordination chemistry is a versatile greener alternative to conventional synthesis, offering quantitative yields, enhanced stoichiometric and topological selectivity, access to a wider range of precursors, as well as to molecules and materials not readily accessible in solution or solvothermally. With a focus on mechanochemical, thermochemical and “accelerated aging” approaches to coordination polymers, including pharmaceutically-relevant materials and microporous MOFs, this review highlights the recent advances in solid-state coordination chemistry and techniques for understanding the underlying reaction mechanisms.

Polyethylene glycol derivatization of the non-active ion in active pharmaceutical ingredient ionic liquids enhances transdermal delivery

Introducing PEGylated moieties into the counterion structure of API–ILs can significantly enhance the transport through a membrane without a solvent.

Rapid Discrimination of Polymorphic Crystal Forms by Nonlinear Optical Stokes Ellipsometric Microscopy

The use of nonlinear optical Stokes ellipsometric (NOSE) microscopy for rapid discrimination of two polymorphic forms of the small molecule d-mannitol is presented. Fast (8 MHz) polarization modulated beam-scanning microscopy and a recently developed iterative, nonlinear least-squares fitting algorithm were combined to allow discrimination of orthorhombic and monoclinic crystal structures of d-mannitol with data acquisition times of <7 s per field of view with a signal-to-noise ratio (SNR) of ∼300. Discrimination between polymorphic forms within the 99.99% confidence interval was achieved by standard statistical tests of the recovered probability density functions for the measured observables following two class linear discriminant analysis. These measurements target bottlenecks in small-volume, high-throughput solid form screening experiments for polymorph discovery in the development of emerging active pharmaceutical ingredients.