Co-amorphous systems for the delivery of poorly water-soluble drugs: recent advances and an update

Breaking barriers: enhancing solubility and dissolution of efonidipine using co-amorphous formulations

The study aims to enhance the solubility and dissolution characteristics of efonidipine hydrochloride ethanolate (EFD), an antihypertensive drug, through the co-amorphous approach. Hypertension is a prevalent chronic condition characterized by consistently elevated blood pressure. Efonidipine, a BCS class II drug, has high permeability but low solubility, limiting its therapeutic effectiveness. Amorphization, which disrupts the crystal lattice of crystalline medications, can significantly enhance drug solubility and dissolution rates. Co-amorphous systems of EFD were prepared using solvent evaporation, ball milling, and liquid-assisted grinding methods. The drug and co-former were used in a different ratio, a stoichiometric proportion known for forming stable amorphous phases. The in vitro dissolution of the co-amorphous form was evaluated and compared with the pure crystalline form of EFD. The co-amorphous system of EFD with benzoic acid demonstrated significantly higher dissolution rates in vitro compared to the pure drug. PXRD analysis confirmed the transformation from a crystalline to an amorphous state, indicated by the disappearance of sharp peaks characteristic of the crystalline form. The resultant co-amorphous system exhibited dissolution properties. The co-amorphous approach effectively improved the solubility and dissolution of efonidipine hydrochloride ethanolate. Benzoic acid, as a co-former, facilitated the formation of a stable amorphous phase, thereby enhancing the drug's dissolution rate. The developed a co-amorphous system of EFD with benzoic acid, significantly enhancing its dissolution characteristics. PXRD analysis confirmed the amorphous nature and improved stability of the co-amorphous form, indicating its potential for better therapeutic efficacy in hypertension management.

Monophasic coamorphous sulpiride: a leap in physicochemical attributes and dual inhibition of GlyT1 and P-glycoprotein, supported by experimental and computational insights

Study aimed to design and development of a supramolecular formulation of sulpiride (SUL) to enhance its solubility, dissolution and permeability by targeting a novel GlyT1 inhibition mechanism. SUL is commonly used to treat gastric and duodenal ulcers, migraine, anti-emetic, anti-depressive and anti-dyspeptic conditions. Additionally, Naringin (NARI) was incorporated as a co-former to enhance the drug's intestinal permeability by targeting P-glycoprotein (P-gp) efflux inhibition. NARI, a flavonoid has diverse biological activities, including anti-apoptotic, anti-oxidant, and anti-inflammatory properties. This study aims to design and develop a supramolecular formulation of SUL with NARI to enhance its solubility, dissolution, and permeability by targeting a novel GlyT1 inhibition mechanism, extensive experimental characterization was performed using solid-state experimental techniques in conjunction with a computational approach. This approach included quantum mechanics-based molecular dynamics (MD) simulation and density functional theory (DFT) studies to investigate intermolecular interactions, phase transformation and various electronic structure-based properties. The findings of the miscibility study, radial distribution function (RDF) analysis, quantitative simulations of hydrogen/π-π bond interactions and geometry optimization aided in comprehending the coamorphization aspects of SUL-NARI Supramolecular systems. Molecular docking and MD simulation were performed for detailed binding affinity assessment and target validation. The solubility, dissolution and ex-vivo permeability studies demonstrated significant improvements with 31.88-fold, 9.13-fold and 1.83-fold increments, respectively. Furthermore, biological assessments revealed superior neuroprotective effects in the SUL-NARI coamorphous system compared to pure SUL. In conclusion, this study highlights the advantages of a drug-nutraceutical supramolecular formulation for improving the solubility and permeability of SUL, targeting novel schizophrenia treatment approaches through combined computational and experimental analyses.

Design of indomethacin novel small molecule hydrogels for concomitant release and permeability increases

With the expansion of gel research, organic small molecule gels are beginning to gain attention. Whether the small-molecule gel approach can be a new formulation strategy of solubilization and permeation promotion for poorly soluble drugs needs to be explored in this study. The model ingredient indomethacin (IND) as a nonsteroidal anti-flammatory drug shows limited therapeutic application mainly due to its low water solubility. Herein, the IND small molecule hydrogel was design to co-formed with a small molecule ligand by integrating theory-model-experiment techniques. Then, the formed IND small molecule hydrogels (i.e., IND-MEG hydrogel and IND-ARG hydrogel) with meglumine (MEG) or arginine (ARG) appeared typical 3-D network with good rheology. In comparison to crystalline IND, the solubilities of IND-MEG hydrogel and IND-ARG hydrogel exhibited 506.71-fold and 479.63-fold improvements, respectively. Meanwhile, both IND hydrogels performed significantly enhanced release rate and degree, and maintained supersaturation for a long time arising from the complexation reaction of IND and ligand, which was revealed by phase solubility and fluorescence quenching studies. Furthermore, the designed IND hydrogels significantly promoted IND membrane permeability compared to the commercial IND hydrogel, and enhanced the development potential of novel IND hydrogels for oral and transdermal applications. Therefore, this study provides a new formulation technique to increase the solubility/release and permeability of poorly water-soluble drugs by designing their small molecule hydrogel systems.

Piperine as a molecular bridge mediates a ternary coamorphous system of polyphenols with enhanced pharmaceutical properties

The coamorphous formulations have attracted increasing interest due to enhanced solubility and bioavailability, together with synergistic pharmacological effects. In this study, a ternary coamorphous system of polyphenols was successfully prepared, wherein baicalein (Bai) and resveratrol (Res) were constructed into a single-phase coamorphous system mediated by piperine (Pip). FTIR and ss 13C NMR spectra together with quantum chemical calculation and molecular dynamics simulation suggested Pip as a molecular bridge connected Bai and Res molecules through π-π stacking and hydrogen bonding interactions. The configuration of coamorphous Bai-Pip-Res could minimize the system energy to facilitate its formation and enhance the stability. The ternary system showed 3.2, 4.3 and 5.3-fold increase in apparent solubilities of Bai, Res and Pip, and maintained the peak concentrations for at least 24 h. Compared to binary coamorphous systems, the ternary system exhibited superior physical stability under temperature and humidity conditions. Furthermore, coamorphous Bai-Pip-Res exhibited enhanced antibacterial activity, significant antioxidant ability and synergistic anti-inflammatory effect. This work offers a promising strategy to construct a ternary coamorphous delivery system with enhanced pharmaceutical properties by incorporating a molecular bridge, especially for components with the lack of intermolecular interactions.

Multi-method coamorphous systems of lumefantrine with alpha ketoglutaric acid: Comprehensive characterization, biological evaluation and stability analysis

The coamorphous systems (CAM) of lumefantrine (LMF) and alpha-ketoglutaric acid (KGA) were developed using three different methods to address the solubility and bioavailability limitations of LMF. Powder X-ray diffraction spectroscopy (PXRD) and the differential scanning calorimetry (DSC) confirmed the complete amorphization of the three CAM by the halo pattern and glass transition temperature (Tg), respectively. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and nuclear magnetic resonance spectroscopy (NMR) results indicated that intermolecular interactions existed in the three CAM. Solid-state molecular dynamics simulations revealed the different intermolecular disordered environments present in all three CAM. Solubility analysis showed 14.73×, 12.8× and 9.81× improvement in the liquid-assisted grinding-based coamorphous system (CAM LAG), solvent evaporation-based coamorphous system (CAM SE) and quench-cool-based coamorphous system (CAM QC), respectively, compared to LMF crystalline (LMF CRY). In the in-vitro dissolution experiment 2.63-, 2.16- and 2.17-times increments were observed in CAM LAG, CAM SE and CAM QC compared to LMF CRY, respectively. In-vivo pharmacokinetics study revealed 10.86-, 9.24- and 8.46- folds increments in Cmax of CAM LAG, CAM SE and CAM QC, respectively, compared to LMF CRY. All three CAM illustrated anti-cancer activity in the A549 lung cancer cell line. Molecular dynamics simulation of LMF and KGA with Epidermal growth factor receptor (EGFR), a target for lung cancer treatment, revealed good binding affinity and stability. Stability studies performed under accelerated storage (40°C/75% RH) and extreme environmental conditions indicated that all three CAM have good stability. Different methods based prepared CAM have shown different physicochemical properties, bioavailability and stability profiles. These findings suggest that LMF-KGA CAM effectively addresses the solubility and bioavailability challenges of LMF, potentially leading to better therapeutic outcomes in lung cancer treatment.

Enhancing Patient-Centric Drug Development: Coupling Hot Melt Extrusion with Fused Deposition Modeling and Pressure-Assisted Microsyringe Additive Manufacturing Platforms with Quality by Design

In recent years, with the increasing patient population, the need for complex and patient-centric medications has increased enormously. Traditional manufacturing techniques such as direct blending, high shear granulation, and dry granulation can be used to develop simple solid oral medications. However, it is well known that "one size fits all" is not true for pharmaceutical medicines. Depending on the age, sex, and disease state, each patient might need a different dose, combination of medicines, and drug release pattern from the medications. By employing traditional practices, developing patient-centric medications remains challenging and unaddressed. Over the last few years, much research has been conducted exploring various additive manufacturing techniques for developing on-demand, complex, and patient-centric medications. Among all the techniques, nozzle-based additive manufacturing platforms such as pressure-assisted microsyringe (PAM) and fused deposition modeling (FDM) have been investigated thoroughly to develop various medications. Both nozzle-based techniques involve the application of thermal energy. However, PAM can also be operated under ambient conditions to process semi-solid materials. Nozzle-based techniques can also be paired with the hot melt extrusion (HME) process for establishing a continuous manufacturing platform by employing various in-line process analytical technology (PAT) tools for monitoring critical process parameters (CPPs) and critical material attributes (CMAs) for delivering safe, efficacious, and quality medications to the patient population without compromising critical quality attributes (CQAs). This review covers an in-depth discussion of various critical parameters and their influence on product quality, along with a note on the continuous manufacturing process, quality by design, and future perspectives.

The Effects of Novel Co-Amorphous Naringenin and Fisetin Compounds on a Diet-Induced Obesity Murine Model

BACKGROUND/OBJECTIVE

In recent studies, it has been shown that dietary bioactive compounds can produce health benefits; however, it is not known whether an improvement in solubility can enhance their biological effects. Thus, the aim of this work was to study whether co-amorphous (CoA) naringenin or fisetin with enhanced solubility modify glucose and lipid metabolism, thermogenic capacity and gut microbiota in mice fed a high-fat, high-sucrose (HFSD) diet.

METHODS

Mice were fed with an HFSD with or without CoA-naringenin or CoA-fisetin for 3 months. Body weight, food intake, body composition, glucose tolerance, hepatic lipid composition and gut microbiota were assessed.

RESULTS

CoA-naringenin demonstrated significant reductions in fat-mass gain, improved cholesterol metabolism, and enhanced glucose tolerance. Mice treated with CoA-naringenin gained 45% less fat mass and exhibited improved hepatic lipid profiles, with significant reductions seen in liver triglycerides and cholesterol. Additionally, both CoA-flavonoids increased oxygen consumption (VO2), contributing to enhanced energy expenditure and improved metabolic flexibility. Thermogenic activation, indicated by increased UCP1 and PGC-1α levels, was observed with CoA-fisetin, supporting its role in fat oxidation and adipocyte size reduction. Further, both CoA-flavonoids modulated gut microbiota, restoring diversity and promoting beneficial bacteria, such as Akkermansia muciniphila, which has been linked to improved metabolic health.

CONCLUSIONS

These findings suggest that co-amorphous naringenin or fisetin offers promising applications in improving solubility, metabolic health, and thermogenesis, highlighting the potential of both as therapeutic agents against obesity and related disorders.

Co-Amorphization, Dissolution, and Stability of Quench-Cooled Drug-Drug Coamorphous Supersaturating Delivery Systems with RT-Unstable Amorphous Components

Background: Supersaturating drug delivery systems (SDDSs) have gained significant attention as a promising strategy to enhance the solubility and bioabsorption of Biopharmaceutics Classification System (BCS) II drugs. To overcome challenges associated with polymer-based amorphous SDDS (aSDDS), coamorphous (CAM) systems have emerged as a viable alternative. Among them, "drug-drug" CAM (ddCAM) systems show considerable potential for combination drug therapy. However, many drugs in their pure amorphous forms are unstable at room temperature (RT), complicating their formation and long-term stability profiles. Consequently, limited knowledge exists regarding the behavior of ddCAMs containing RT-unstable components formed via quench cooling. Methods: In this study, we used naproxen (NAP), a RT-unstable amorphous drug, in combination with felodipine (FEL) or nitrendipine (NTP), two RT-stable amorphous drugs, to create "FEL-NAP" and "NTP-NAP" ddCAM pairs via quench cooling. Our work used a series of methods to perform a detailed analysis on the co-amorphization, dissolution, solubility, and stability profiles of ddCAMs containing RT-unstable drugs, contributing to advancements in co-amorphization techniques for generating SDDS. Results: This study revealed that the co-amorphization and stability profiles of ddCAMs containing RT-unstable components produced via a quench-cooling method were closely related to drug-drug pairing types and ratios. Both quench-cooling and incorporation into coamorphous systems improved the dissolution, solubility, and physical stability of individual APIs. Conclusions: Our findings provide deeper insight into the co-amorphization, dissolution, and stability characteristics of specific drug-drug coamorphous systems FEL-NAP and NTP-NAP, offering valuable guidance for developing new ddCAM coamorphous formulations containing some RT-unstable drugs.

Amphiphilic disodium glycyrrhizin as a co-former for ketoconazole co-amorphous systems: Biopharmaceutical properties and underlying molecular mechanisms

Co-amorphous systems (CAMs) have been extensively investigated to improve the dissolution of hydrophobic drugs. However, drug precipitation during the storage or dissolution of CAMs has still been a major challenge. Here, disodium glycyrrhizin (Na2GA) was first used as a co-former in CAMs based on its multiple hydroxyl groups and amphiphilic structure. Ketoconazole (KTZ), a BCS class II drug, was selected as a model drug. KTZ-Na2GA CAMs at mass ratios of 1:1, 1:2.5, 1:5 and 1:10 were prepared by the spray drying method and further characterised by PXRD and DSC. The 1:2.5, 1:5 and 1:10 groups exhibited significantly enhanced Cmax (all approximately 26.67-fold) and stable maintenance of supersaturation compared to the crystalline KTZ and the corresponding physical mixtures in non-sink dissolution tests, while the 1:1 group exhibited an unstable medium Cmax (all approximately 14.67-fold). The permeability tests revealed that the permeation rate of KTZ in KTZ-Na2GA CAMs under the concentration of Na2GA in solution above the critical micelle concentration (CMC) showed a significant downwards trend compared to that below CMC. The underlying molecular mechanisms were involved in molecular miscibility, hydrogen bond interactions, solubilisation and crystallisation inhibition by Na2GA. Pharmacokinetic studies demonstrated that the AUC0-∞ of KTZ in 1:1, 1:2.5, 1:5 and 1:10 groups were significantly higher than those of the crystalline KTZ group with 2.13-, 2.30-, 2.16- and 1.86-fold, respectively (p < 0.01). In conclusion, Na2GA has proven to be a promising co-former in CAMs to enhance hydrophobic drug dissolution and bioavailability. Its effect on intestinal permeation rate of drugs also deserves attention.

Counter-intuitive discovery in the formulation of poorly water-soluble drugs: Amorphous small-molecule gels

Amorphous strategies have been extensively used in improving the dissolution of insoluble drugs for decades due to their high free energy. However, the formation of amorphous small-molecule gels (ASMGs) presents a counter-intuitive discovery that significantly limits their practical application. Recently, ASMGs have garnered attention because of their noncovalent structures, excellent biodegradability, and significant potential in various drug delivery systems in the pharmaceutical field. Hence, a comprehensive review is necessary to contribute to a better understanding of recent advances in ASMGs. This review aimed to introduce the main formation mechanisms, summarize possible influencing factors, generalize unique properties, outline elimination strategies, and discuss clinical application potential with preclinical cases of ASMGs. Moreover, few ASMGs are advanced to clinical stages. Intensive clinical research is needed for further development. We hope that this review can provide more efficient and rational guidance for exploring further clinical applications of ASMGs.

Study on co-amorphous emerging solubilization behavior after gelation during dissolution: The importance of complexation and anti-crystallization

Co-amorphous (CM) is a promising technology for enhancing the aqueous solubility of insoluble drugs, but the gelation phenomenon has often occurred during the dissolution process and seriously threatened their solubility/dissolution performance. Therefore, it's quite important to design favorable CM systems to alleviate or even avoid the adverse effects of gelation phenomenon. In this study, CM systems of taxifolin (TAX) and oxymatrine (OMT) (TAX-OMT CMs) were constructed to improve the solubility and dissolution properties of TAX. Interestingly, TAX-OMT CMs gradually aggregated and obviously gelled during dissolution, but the solubility and dissolution of TAX in TAX-OMT CMs were significantly enhanced compared to crystalline TAX. Consequently, the underlying solubilization mechanisms of TAX-OMT CMs after gelation were systematically explored. For one thing, the complexation between the two components in TAX-OMT CMs was verified by phase solubility, fluorescence spectroscopy and isothermal titration calorimetry. For another, the residual solids of TAX-OMT CMs after dissolution evaluation were thoroughly characterized by means of powder X-ray diffraction, fourier transform infrared spectroscopy, scanning electron microscopy, which showed the anti-crystallization property of TAX-OMT CMs. Furthermore, molecular simulation demonstrated the intermolecular interactions of TAX-OMT CMs alone and TAX-OMT complexes in aqueous solution. Finally, pharmacokinetics study in rats suggested that the bioavailability of TAX in TAX-OMT CM (1:2) was approximately 5.5-fold higher than that of crystalline TAX after oral administration. Collectively, this study reveals the importance of complexation and anti-crystallization effects of CM systems on maintaining solubilization behavior after gelation, providing an effective strategy to improve the absorption performance of pharmaceutical CM systems.

Exploring Co-Amorphous Formulations Of Nevirapine: Insights From Computational, Thermal, And Solubility Analyses

This study aimed to assess the formation of nevirapine (NVP) co-amorphs systems (CAM) with different co-formers (lamivudine-3TC, citric acid-CAc, and urea) through combined screening techniques as computational and thermal studies, solubility studies; in addition to develop and characterize suitable NVP-CAM. NVP-CAM were obtained using the quench-cooling method, and characterized by differential scanning calorimetry (DSC), X-ray diffractometry (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and polarized light microscopy (PLM), in addition to in vitro dissolution in pH 6.8. The screening results indicated intermolecular interactions occurring between NVP and 3TC; NVP and CAc, where shifts in the melting temperature of NVP were verified. The presence of CAc impacted the NVP equilibrium solubility, due to hydrogen bonds. DSC thermograms evidenced the reduction and shifting of the endothermic peaks of NVP in the presence of its co-formers, suggesting partial miscibility of the compounds. Amorphization was proven by XRD and PLM assays. In vitro dissolution study exhibited a significant increase in solubility and dissolution efficiency of NVP-CAM compared to free NVP. Combined use of screening studies was useful for the development of stable and amorphous NVP-CAM, with increased NVP solubility, making CAM promising systems for combined antiretroviral therapy.

Specific intermolecular interaction with sodium glycocholate generates the co-amorphous system showing higher physical stability and aqueous solubility of Y5 receptor antagonist of neuropeptide Y, a brick dust molecule

Drugs with poor water and lipid solubility are termed "brick dust." We previously successfully developed a co-amorphous system of a novel neuropeptide Y5 receptor antagonist (AntiY5R), a brick dust molecule, using sodium taurocholate (NaTC) as a co-former. However, the maximum improvement in AntiY5R dissolution by the co-amorphous system was only approximately 10 times greater than that of the crystals. Therefore, in the current study, other bile salts, including sodium cholate (NaC), sodium chenodeoxycholate (NaCC), and sodium glycocholate (NaGC), were examined as co-formers to further improve AntiY5R dissolution. NaC, NaCC, and NaGC have glass transition temperatures above 150°C. All three co-amorphous systems prepared successfully retained the amorphous form of AntiY5R for 3 months at 40°C, but the co-amorphous system with NaGC (AntiY5R-NaGC; 1:9 molar ratio) provided the highest improvement in AntiY5R dissolution, which was approximately 50 times greater than that of the crystals. Possible intermolecular interactions via the glycine moiety of NaGC more than the other bile salts would contribute to the highest dissolution enhancement with AntiY5R-NaGC. Thus, NaGC would be a promising co-former for formulating stable co-amorphous systems to enhance the dissolution behavior of brick dust molecules.

Insight into Formation, Synchronized Release and Stability of Co-Amorphous Curcumin-Piperine by Integrating Experimental-Modeling Techniques

Intermolecular interactions between drug and co-former are crucial in the formation, release and physical stability of co-amorphous system. However, the interactions remain difficult to investigate with only experimental tools. In this study, intermolecular interactions of co-amorphous curcumin-piperine (i.e., CUR-PIP CM) during formation, dissolution and storage were explored by integrating experimental and modeling techniques. The formed CUR-PIP CM exhibited the strong hydrogen bond interaction between the phenolic OH group of CUR and the CO group of PIP as confirmed by FTIR, ss 13C NMR and molecular dynamics (MD) simulation. In comparison to crystalline CUR, crystalline PIP and their physical mixture, CUR-PIP CM performed significantly increased dissolution accompanied by the synchronized release of CUR and PIP, which arose from the greater interaction energy of H2O-CUR molecules and H2O-PIP molecules than CUR-PIP molecules, breaking the hydrogen bond between CUR and PIP molecules, and then causing a pair-wise solvation of CUR-PIP CM at the molecular level. Furthermore, the stronger intermolecular interaction between CUR and PIP was revealed by higher binding energy of CUR-PIP molecules, which contributed to the excellent physical stability of CUR-PIP CM over amorphous CUR or PIP. The study provides a unique insight into the formation, release and stability of co-amorphous system from MD perspective. Meanwhile, this integrated technique can be used as a practical methodology for the future design of co-amorphous formulations.

Nucleotides as new co-formers in co-amorphous systems: Enhanced dissolution rate, water solubility and physical stability

Developing co-amorphous systems is an attractive strategy to improve the dissolution rate of poorly water-soluble drugs. Various co-formers have been investigated. However, previous studies revealed that it is a challenge to develop satisfied acidic co-formers, e.g., acidic amino acids showed much poorer co-former properties than neutral and basic amino acids. Only a few acidic co-formers have been reported, such as aspartic acid, glutamic acid, and some other organic acids. Thus, this study aims to explore the possibility of adenosine monophosphate and adenosine diphosphate used as acidic co-formers. Mebendazole, celecoxib and tadalafil were used as the model drugs. The drug-co-former co-amorphous systems were prepared via ball milling and confirmed using XRPD. The dissolution study suggested that the solubility and dissolution rate of the drug-co-formers systems were increased significantly compared to the corresponding crystalline and amorphous drugs. The stability study revealed that using the two nucleotides as co-formers enhanced the physical stability of pure amorphous drugs. Molecular interactions were observed in MEB-co-former and TAD-co-former systems and positively affected the pharmaceutical performance of the investigated co-amorphous systems. In conclusion, the two nucleotides could be promising potential acidic co-formers for co-amorphous systems.

Recent developments in the use of nanocrystals to improve bioavailability of APIs

Nanocrystals refer to materials with at least one dimension smaller than 100 nm, composing of atoms arranged in single crystals or polycrystals. Nanocrystals have significant research value as they offer unique advantages over conventional pharmaceutical formulations, such as high bioavailability, enhanced targeting selectivity and controlled release ability and are therefore suitable for the delivery of a wide range of drugs such as insoluble drugs, antitumor drugs and genetic drugs with broad application prospects. In recent years, research on nanocrystals has been progressively refined and new products have been launched or entered the clinical phase of studies. However, issues such as safety and stability still stand that need to be addressed for further development of nanocrystal formulations, and significant gaps do exist in research in various fields in this pharmaceutical arena. This paper presents a systematic overview of the advanced development of nanocrystals, ranging from the preparation approaches of nanocrystals with which the bioavailability of poorly water-soluble drugs is improved, critical properties of nanocrystals and associated characterization techniques, the recent development of nanocrystals with different administration routes, the advantages and associated limitations of nanocrystal formulations, the mechanisms of physical instability, and the enhanced dissolution performance, to the future perspectives, with a final view to shed more light on the future development of nanocrystals as a means of optimizing the bioavailability of drug candidates. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Molecular interactions of hydrated co-amorphous systems of prilocaine and lidocaine

It is generally accepted that water as a plasticizer can decrease the glass transition temperatures (Tgs) of amorphous drugs and drug excipient systems. However, previous studies suggest that water, as an anti-plasticizer, can increase the Tgs of co-amorphous systems of prilocaine (PRL) and lidocaine (LID). In order to investigate the intermolecular interactions between water and co-amorphous PRL-LID systems, Fourier transform infrared spectroscopy (FTIR) and principal component analysis (PCA) were conducted. Water was found to bind with the carbonyl groups of PRL and LID molecularly evenly in the hydrated co-amorphous PRL-LID systems. Quantum chemical simulations visually confirmed the interactions between water and co-amorphous PRL-LID systems. Furthermore, the physical stability of hydrated co-amorphous PRL-LID systems was improved due to the anti-plasticizing effect of water, compared with the anhydrous samples. The preference of water to interact with the carbonyl groups of PRL and LID as binding sites could be associated with the anti-plasticizing effect of water on the co-amorphous PRL-LID systems.

Recent advances in dual-drug co-amorphous systems

Poor solubility of drugs and therapeutic candidates poses a significant challenge in drug research and development. Biopharmaceutical class II drugs exhibit limited absorption because of their weak solubility and high permeability. Co-amorphous systems (CAMs) have been studied widely as a way to improve the solubility of drugs. This review summarizes recent advancements in dual-drug CAMs, including improvements in formulation, manufacturing, and solid-state characterization, and highlights the importance of enhancing solubility and stability. It emphasizes the potential synergistic effects of two drugs in CAMs and explores formulation strategies and challenges related to maintaining the amorphous state. Case studies demonstrate the successful application of CAMs in combination therapies that offer improved therapeutic efficacy.

Drug-drug co-amorphous systems: An emerging formulation strategy for poorly water-soluble drugs

Overcoming the poor water solubility of small-molecule drugs is a major challenge in the development of clinical pharmaceuticals. Amorphization of crystalline drugs is a highly effective strategy to improve their aqueous solubility. However, amorphous drugs are thermodynamically unstable and likely to crystallize during manufacturing and storage. Recently, drug-drug co-amorphous systems have emerged as a novel strategy to not only enable enhanced dissolution and physical stability of the individual drugs within the system but also to provide a strategy for combination therapy of the same or different clinical indications. This review serves to highlight advances in the methods used to manufacture and characterize drug-drug co-amorphous systems, summarize drug-drug co-amorphous applications reported in recent decades, and provide an outlook on future possibilities and perspectives.

Opportunities and challenges in enhancing the bioavailability and bioactivity of dietary flavonoids: A novel delivery system perspective

Flavonoids have multiple favorable bioactivities including antioxidant, anti-inflammatory, and antitumor. Currently, flavonoid-containing dietary supplements are widely tested in clinical trials for the prevention and/or treatment of multiple diseases. However, the clinical application of flavonoids is largely compromised by their low bioavailability and bioactivity, probably due to their poor aqueous solubility, intensive metabolism, and low systemic absorption. Therefore, formulating flavonoids into novel delivery systems is a promising approach for overcoming these drawbacks. In this review, we highlight the opportunities and challenges in the clinical use of dietary flavonoids from the perspective of novel delivery systems. First, the classification, sources, and bioactivity of dietary flavonoids are described. Second, the progress of clinical research on flavonoid-based dietary supplements is systematically summarized. Finally, novel delivery systems developed to improve the bioavailability and bioactivity of flavonoids are discussed in detail to broaden the clinical application of dietary flavonoids.

Amorphization of Low Soluble Drug with Amino Acids to Improve Its Therapeutic Efficacy: a State-of-Art-Review

Low aqueous solubility of drug candidates is an ongoing challenge and pharmaceutical manufacturers pay close attention to amorphization (AMORP) technology to improve the solubility of drugs that dissolve poorly. Amorphous drug typically exhibits much higher apparent solubility than their crystalline form due to high energy state that enable them to produce a supersaturated state in the gastrointestinal tract and thereby improve bioavailability. The stability and augmented solubility in co-amorphous (COA) formulations is influenced by molecular interactions. COA are excellent carriers-based drug delivery systems for biopharmaceutical classification system (BCS) class II and class IV drugs. The three important critical quality attributes, such as co-formability, physical stability, and dissolution performance, are necessary to illustrate the COA systems. New amorphous-stabilized carriers-based fabrication techniques that improve drug loading and degree of AMORP have been the focus of emerging AMORP technology. Numerous low-molecular-weight compounds, particularly amino acids such as glutamic acid, arginine, isoleucine, leucine, valine, alanine, glycine, etc., have been employed as potential co-formers. The review focus on the prevailing drug AMORP strategies used in pharmaceutical research, including in situ AMORP, COA systems, and mesoporous particle-based methods. Moreover, brief characterization techniques and the application of the different amino acids in stabilization and solubility improvements have been related.

Improvement in Inhalation Properties of Theophylline and Levofloxacin by Co-Amorphization and Enhancement in Its Stability by Addition of Amino Acid as a Third Component

Co-amorphous systems are amorphous formulations stabilized by the miscible dispersion of small molecules. This study aimed to design a stable co-amorphous system for the co-delivery of two drugs to the lungs as an inhaled formulation. Theophylline (THE) and levofloxacin (LEV) were used as model drugs for treating lung infection with inflammation. Leucine (LEU) or tryptophan (TRP) was employed as the third component to improve the inhalation properties. The co-amorphous system containing THE and LEV in an equal molar ratio was successfully prepared via spray drying where reduction of the particle size and change to the spherical morphology were observed. The addition of LEU or TRP at a one-tenth molar ratio to THE-LEV did not affect the formation of the co-amorphous system, but only TRP acted as an antiplasticizer. The Fourier transform infrared spectroscopy spectra revealed intermolecular interactions between THE and LEV in the co-amorphous system that were retained after the addition of LEU or TRP. The co-amorphous THE-LEV system exhibited better in vitro aerodynamic performance than a physical mixture of these compounds and permitted the simultaneous delivery of both drugs in various stages. The co-amorphous THE-LEV system crystallized at 40 °C, and this crystallization was not prevented by LEU. However, THE-LEV-TRP maintained its amorphous state for 1 month. Thus, TRP can act as a third component to improve the physical stability of the co-amorphous THE-LEV system, while maintaining the enhanced aerodynamic properties.

Amorphous solid dispersions: Stability mechanism, design strategy and key production technique of hot melt extrusion

Solid dispersion (SD) system has been used as an effective formulation strategy to increase in vitro and in vivo performances of poorly water-soluble drugs, such as solubility/dissolution, stability and bioavailability. This review provides a comprehensive SD classification and identifies the most popular amorphous solid dispersions (ASDs). Meanwhile, this review further puts forward the systematic design strategy of satisfactory ASDs in terms of drug properties, carrier selection, preparation methods and stabilization mechanisms. In addition, hot melt extrusion (HME) as the continuous manufacturing technique is described including the principle and structure of HME instrument, key process parameters and production application, in order to guide the scale-up of ASDs and develop more ASD products to the market in pharmaceutical industry.

Cyclosporine A-loaded chitosan extra-fine particles for deep pulmonary drug delivery: In vitro and in vivo evaluation

In this study, the extra-fine dry powder inhalers (DPIs) with chitosan (CS) as carrier were successfully prepared by ionic gel method combined with spray drying technique for deep pulmonary drug delivery of Cyclosporine A (CsA), using sodium hyaluronate (SHA) and sodium polyglutamate (SPGA) as polyanions. The CsA-loaded DPIs of CS-SHA-CsA and CS-SPGA-CsA were spherical particles with wrinkles on the surface, which were more conducive to improving the aerosol properties. The aerodynamic evaluation of CS-SHA-CsA and CS-SPGA-CsA showed that the fine particle fraction (FPF) reached up to 79.22 ± 2.12% and 81.55 ± 0.43%, while the emitted fraction (EF) reached 77.15 ± 1.46% and 78.29 ± 2.10%. In addition, the mass median aerodynamic diameter (MMAD) was calculated as 1.58 ± 0.04 μm and 1.94 ± 0.02 μm for CS-SHA-CsA and CS-SPGA-CsA, indicating that they were all extra-fine particles (d < 2 μm). These in vitro aerodynamic results showed that CS-SHA-CsA and CS-SPGA-CsA could reach the smaller airways, further improving therapeutic efficiency. The cell viability on A549 cell line results showed that CS-SHA-CsA and CS-SPGA-CsA were safe to deliver CsA to lungs. The in vivo pharmacokinetics consequence proved that inhalation administration of CS-SHA-CsA and CS-SPGA-CsA could significantly improve the bioavailability of CsA in vivo compared with oral administration of Neoral®, effectively reducing the risk of a series of adverse effects caused by systemic overexposure. In addition, the safety and compatibility of DPIs using SHA, SPGA, and CS as carriers for pulmonary drug delivery was verified by in vivo repeated dose inhalation toxicity. From these findings, the extra-fine DPIs with CS as carrier could be a viable delivery option for the deep pulmonary drug delivery of CsA relative to orally administered drug.

Wet granulation of co-amorphous indomethacin systems

The feasibility of co-amorphous systems to be wet granulated together with microcrystalline cellulose (MCC) was investigated. Solid state and molecular interactions were analysed for various co-amorphous drug-amino acid formulations of indomethacin with tryptophan and arginine, respectively, via XRPD, DSC and FTIR. The co-amorphous binary systems were produced by ball-milling for 90 min at different molar ratios followed by wet granulation with MCC and water in a miniaturised scale. Tryptophan containing systems showed crystalline reflections in their XRPD diffractograms and endothermal events in their DSC analyses, and were therefore excluded from upscaling attempts. The systems containing arginine were found to be remain amorphous for at least ten months and were upscaled for production in a high-shear blender under application of two different parameter settings. Under the harsher instrument settings, a composition with a low MCC ratio experienced recrystallisation during wet granulation, while all other compositions could be successfully processed via wet granulation and stayed stable for a storage period of at least twelve weeks, indicating that wet granulation of co-amorphous systems can be feasible.

Dissolution changes in drug-amino acid/biotin co-amorphous systems: Decreased/increased dissolution during storage without recrystallization

Co-amorphous systems have been proven to be a promising strategy to address the poor water solubility of poorly water-soluble drugs. Generally, the initial dissolution behaviors after co-amorphous system preparation and the potential recrystallization during storage are used to evaluate the performance of co-amorphous systems. However, this study reveals that decreased dissolution and unexpected increased dissolution were observed during storage though the co-amorphous systems maintained amorphous form. Three drugs (valsartan, tadalafil, mebendazole) and three co-formers (arginine, tryptophan, biotin) were used to prepare co-amorphous systems and the samples were stored for different times. After stored for 80 d, most of the co-amorphous systems maintained amorphous form, however, decreased and increased intrinsic dissolution rates (IDRs) were both observed in these non-recrystallized co-amorphous systems. The moisture changes of the systems during storage and the possible drug-co-former molecular interactions showed no effect on the dissolution changes, while phase separation might play a role in it. In conclusion, more attention should be paid to the dissolution changes of co-amorphous systems during storage. Focusing on the initial dissolution behaviors after sample preparation and the physical recrystallization during storage is not enough for the development of co-amorphous systems in future.

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.

Ternary Solid Dispersions: A Review of the Preparation, Characterization, Mechanism of Drug Release, and Physical Stability

The prevalence of active pharmaceutical ingredients (APIs) with low water solubility has experienced a significant increase in recent years. These APIs present challenges in formulation, particularly for oral dosage forms, despite their considerable therapeutic potential. Therefore, the improvement of solubility has become a major concern for pharmaceutical enterprises to increase the bioavailability of APIs. A promising formulation approach that can effectively improve the dissolution profile and the bioavailability of poorly water-soluble drugs is the utilization of amorphous systems. Numerous formulation methods have been developed to enhance poorly water-soluble drugs through amorphization systems, including co-amorphous formulations, amorphous solid dispersions (ASDs), and the use of mesoporous silica as a carrier. Furthermore, the successful enhancement of certain drugs with poor aqueous solubility through amorphization has led to their incorporation into various commercially available preparations, such as ASDs, where the crystalline structure of APIs is transformed into an amorphous state within a hydrophilic matrix. A novel approach, known as ternary solid dispersions (TSDs), has emerged to address the solubility and bioavailability challenges associated with amorphous drugs. Meanwhile, the introduction of a third component in the ASD and co-amorphous systems has demonstrated the potential to improve performance in terms of solubility, physical stability, and processability. This comprehensive review discusses the preparation and characterization of poorly water-soluble drugs in ternary solid dispersions and their mechanisms of drug release and physical stability.

Promising strategies for improving oral bioavailability of poor water-soluble drugs

INTRODUCTION

Oral administration of poorly water-soluble drugs (PWSDs) is generally related to low bioavailability, leading to high drug doses, multiple side effects, and low patient compliance. Thus, different strategies have been developed to increase drug solubility and dissolution in the gastrointestinal tract, opening new venues for these drugs.

AREAS COVERED

This review outlines the current challenges in PWSD formulation development and the strategies to overcome the oral barriers and increase their solubility and bioavailability. Conventional strategies include altering crystalline and molecular structures and modifying oral solid dosage forms. In contrast, novel strategies comprise micro- and nanostructured systems. Recent representative studies involving how these strategies have improved the oral bioavailability of PWSDs were also reviewed and reported.

EXPERT OPINION

New approaches to enhance PWSD bioavailability have sought to improve water solubility and dissolution rates, drug protection by overcoming biological barriers, and increased absorption. Still, only a handful of studies have focused on quantifying the increase in bioavailability. Improving the oral bioavailability of PWSDs remains an exciting unexplored field of research and has become an important issue for successfully developing pharmaceutical products.

Amorphization of Ethenzamide and Ethenzamide Cocrystals-A Case Study of Single and Binary Systems Forming Low-Melting Eutectic Phases Loaded on/in Silica Gel

The applicability of different solvent-free approaches leading to the amorphization of active pharmaceutical ingredients (APIs) was tested. Ethenzamide (ET), an analgesic and anti-inflammatory drug, and two ethenzamide cocrystals with glutaric acid (GLU) and ethyl malonic acid (EMA) as coformers were used as pharmaceutical models. Calcinated and thermally untreated silica gel was applied as an amorphous reagent. Three methods were used to prepare the samples: manual physical mixing, melting, and grinding in a ball mill. The ET:GLU and ET:EMA cocrystals forming low-melting eutectic phases were selected as the best candidates for testing amorphization by thermal treatment. The progress and degree of amorphousness were determined using instrumental techniques: solid-state NMR spectroscopy, powder X-ray diffraction, and differential scanning calorimetry. In each case, the API amorphization was complete and the process was irreversible. A comparative analysis of the dissolution profiles showed that the dissolution kinetics for each sample are significantly different. The nature and mechanism of this distinction are discussed.

Introduction to Pharmaceutical Co-amorphous Systems Using a Green Co-milling Technique

The concept of co-amorphous systems is introduced in an integrated laboratory experiment, designed for advanced chemistry students, using solvent-free, environmentally friendly mechanochemistry. The dual-drug naproxen-cimetidine co-amorphous system (NPX-CIM) is investigated as an example of the emergent field of medicinal mechanochemistry. Students are trained in solid-state characterization techniques including X-ray powder diffraction, Fourier-transform infrared spectroscopy, and thermal analysis by differential scanning calorimetry. This lab experiment also provides an opportunity to discuss the relevance of different solid forms of pharmaceutics, emphasizing particular properties of disordered materials. This experiment can easily fit the curriculum of any Chemistry or Pharmacy master level degree in courses dealing with instrumental analysis, solid state chemistry, or green chemistry, for classes of 6 to 18 students, in a 5-h lab session. Suggestions to adapt it to the use of a single characterization technique are provided.

Tranilast-matrine co-amorphous system: Strong intermolecular interactions, improved solubility, and physiochemical stability

There is a great interest to develop co-amorphous drug delivery systems to enhance the solubility of biopharmaceutics classification system (BCS) class II and IV drugs. However, most reported systems only resulted in severalfold solubility improvement. Tranilast (TRA) is an anti-allergic drug used to treat bronchial asthma and allergic rhinitis. It is a BCS class II drug and its poor aqueous solubility affects its absorption in vivo. To address this issue, a natural alkaloid matrine (MAR) with interesting biological activities was chosen to form a co-amorphous system with TRA, based on the solubility parameter and phase solubility experiment. The TRA-MAR drug-drug co-amorphous system was prepared by the solvent evaporation method, and further characterized by powder X-ray diffraction and modulated temperature differential scanning calorimetry. Fourier transform infrared spectroscopy, FT-Raman, and X-ray photoelectron spectroscopy revealed the formation of salt and the presence of strong intermolecular interactions in the TRA-MAR co-amorphous system, which are also supported by molecular dynamics simulations, showing ionic and hydrogen bonding interactions. This co-amorphous system exhibited excellent physical stability at both 25 °C and 40 °C under anhydrous silica gel condition. Finally, co-amorphous TRA-MAR showed greatly enhanced solubility (greater than 100-fold) and rapid release behavior in the vitro release experiments. NMR spectroscopy revealed the strong intermolecular interactions between TRA and MAR in both DMSO‑d₆ and D₂O. Our study resulted in a TRA-MAR co-amorphous drug system with significant solubility improvement and showcased the great potential to improve the dissolution behaviors of BCS class II and IV drugs through the co-amorphization approach.

Mechanistic insight into gel formation of co-amorphous resveratrol and piperine during dissolution process

Different from previous co-amorphous systems, co-amorphous resveratrol and piperine (namely RES-PIP CM) showed much lower dissolution in comparison to the original two crystalline drugs owing to its gel formation during dissolution. The purpose of this study is to investigate the mechanism of gel formation and seek strategies to eliminate such gelation. It was found that the dissolution performance of RES-PIP CM and the properties of formed gels were significantly affected by the medium temperature and stoichiometric ratio of components. Multiple characterization results confirmed that the gelation process underwent the decrease of T_g caused by water plasticization, and then entered into its supercooled liquid state with high viscosity, accompanied by self-assembly of molecules. Furthermore, the study answered the question that whether such gelation of RES-PIP CM could be eliminated by porous carrier materials. The materials, mesoporous silica (MES) and attapulgite (ATT), provided barrier and well separation between molecules and particles of RES-PIP CM by the pore steric hindrance, and impeded the self-assembly and aggregation, hence achieving the degelation and dissolution improvement. The present study highlights the importance of recognizing gelation potential of some co-amorphous formulations, and provides an effective strategy to eliminate gelation in developing high quality co-amorphous drug products.

Effect of Solubility Improvement via Formation of an Amorphous Composite of Indomethacin and Sulindac on Membrane Permeability

The importance of permeability as well as solubility of the drug has been recognized in improving the solubility of poorly water-soluble drugs. This study investigated the impact of amorphous composites of indomethacin (IMC) and sulindac (SLD) on the membrane permeability of drugs. The IMC/SLD (1/1) formulation prepared by dry grinding was amorphous with a single glass transition temperature. The Fourier transform IR spectra and Raman spectra revealed formation of hydrogen bonds between the OH group of IMC and the carbonyl group of SLD. These results suggest that an amorphous composite was formed between IMC and SLD through hydrogen bonding. The amount of dissolved IMC and SLD from the amorphous composite of IMC/SLD (1/1) was higher than that of the untreated IMC or SLD in the dissolution test. The permeated amounts and permeation rates of both drugs were enhanced by increasing the solubility of the amorphous composite. Conversely, the apparent membrane permeability coefficients (P_app) were almost same for untreated drugs and amorphous composites. In the case of hydroxypropyl-β-cyclodextrin and sodium dodecyl sulfate, P_app of the drugs decreased with the addition of these compounds, although the drug solubility was enhanced by the solubilization effect. This study revealed that an amorphous composite formed through hydrogen bonding is an attractive pharmaceutical way to enhance the permeated amount and permeation rate without changing the P_app of both the drugs.

Mechanistic insights into the crystallization of coamorphous drug systems

In our previous study, the coamorphous formulation of lurasidone hydrochloride (LH) with saccharin (SAC) showed significantly enhanced dissolution and physical stability compared to crystalline/amorphous LH. However, the coamorphous system is still in amorphous state, and has the tendency to recrystallization, which will in turn result in the loss of above advantages. In this study, the crystallization kinetics under isothermal and non-isothermal conditions was investigated. Compared to amorphous LH, coamorphous LH-SAC showed 68.3-361.2 and 2.6-6.1 times lower crystallization rates in glassy state and supercooled liquid state, respectively. After co-amorphization, the addition of SAC changed the crystallization mechanism of amorphous LH from nucleation-controlled to diffusion-controlled manner. Amorphous LH followed the site-saturated nucleation, whereas the coamorphous system exhibited a fixed number of nuclei. The non-isothermal crystallization indicated amorphous LH and coamorphous LH-SAC showed two-dimensional (JMAEK 2) and three-dimensional (JMAEK 3) growth of nuclei, respectively. Furthermore, coamorphous LH-SAC exhibited higher molecular mobility and dynamic fragility (m_D) than amorphous LH, which is kinetically unfavorable for its physical stability. However, from thermodynamic perspective, coamorphous LH-SAC had a higher configurational entropy, i.e., a higher entropy barrier for crystallization, which is beneficial to hinder its crystallization. Therefore, it was concluded that the higher configurational entropy rather than the molecular mobility was proposed to be responsible for its improved stability. In addition, molecular dynamics simulations with miscibility, radial distribution function and binding energy calculations suggested coamorphous components exhibited good miscibility and strong intermolecular interactions, which was also conductive to the enhancement in its stability. This study offers an in-depth understanding about the effect of the coformer on the crystallization kinetics of coamorphous systems, and points out the important contribution of the configurational entropy in stabilizing the coamorphous systems.

Gelation Elimination and Crystallization Inhibition by Co-Amorphous Strategy for Amorphous Curcumin

In the previous study, the development of amorphous curcumin (CUR) aimed to enhance the solubility/dissolution of CUR by disrupting its crystal lattice, but it unexpectedly showed a decreased dissolution than its crystalline counterpart on account of gel formation in its dissolution process. Whether such gelation could be eliminated by co-amorphous strategy was answered in this study. Herein, CUR by co-amorphization with chlorogenic acid (CHA) was successfully prepared using quench cooling. The formed co-amorphous material (namely CUR-CHA CM) eliminated the gelation and hence performed superior dissolution performance than crystalline/amorphous CUR. Meanwhile, it exhibited higher physical stability than amorphous CUR during dissolution as well as under long-term/accelerated conditions. To further study the such enhancement mechanism, the internal molecular interactions were investigated for CUR-CHA CM in the solid state as well as in aqueous solution. FTIR and solid-state ¹³C NMR spectra confirmed that intermolecular hydrogen bonds formed between CUR and CHA after co-amorphization. Furthermore, the nucleation of CUR was significantly inhibited by CHA in an aqueous solution, thus maintaining the supersaturated dissolution for a long time. The present study offers a feasible strategy to eliminate gelation and enhance stability of amorphous solids by co-amorphization and crystallization inhibition.

Formation of a Stable Co-Amorphous System for a Brick Dust Molecule by Utilizing Sodium Taurocholate with High Glass Transition Temperature

Brick dust molecules are usually poorly soluble in water and lipoidal components, making it difficult to formulate them in dosage forms that provide efficient pharmacological effects. A co-amorphous system is an effective strategy to resolve these issues. However, their glass transition temperatures (Tg) are relatively lower than those of polymeric amorphous solid dispersions, suggesting the instability of the co-amorphous system. This study aimed to formulate a stable co-amorphous system for brick dust molecules by utilizing sodium taurocholate (NaTC) with a higher Tg. A novel neuropeptide Y5 receptor antagonist (AntiY5R) and NaTC with Tg of 155 °C were used as the brick dust model and coformer, respectively. Ball milling formed a co-amorphous system for AntiY5R and NaTC (AntiY5R-NaTC) at various molar ratios. Deviation from the theoretical Tg value and peak shifts in Fourier-transform infrared spectroscopy indicated intermolecular interactions between AntiY5R and NaTC. AntiY5R-NaTC at equal molar ratios resulting in an 8.5-fold increase in AntiY5R solubility over its crystalline form. The co-amorphous system remained amorphous for 1 month at 25 °C and 40 °C. These results suggest that the co-amorphous system formed by utilizing NaTC as a coformer could stably maintain the amorphous state and enhance the solubility of brick dust molecules.

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

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

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

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

Mechanical Activation by Ball Milling as a Strategy to Prepare Highly Soluble Pharmaceutical Formulations in the Form of Co-Amorphous, Co-Crystals, or Polymorphs

Almost half of orally administered active pharmaceutical ingredients (APIs) have low solubility, which affects their bioavailability. In the last two decades, several alternatives have been proposed to modify the crystalline structure of APIs to improve their solubility; these strategies consist of inducing supramolecular structural changes in the active pharmaceutical ingredients, such as the amorphization and preparation of co-crystals or polymorphs. Since many APIs are thermosensitive, non-thermal emerging alternative techniques, such as mechanical activation by milling, have become increasingly common as a preparation method for drug formulations. This review summarizes the recent research in preparing pharmaceutical formulations (co-amorphous, co-crystals, and polymorphs) through ball milling to enhance the physicochemical properties of active pharmaceutical ingredients. This report includes detailed experimental milling conditions (instrumentation, temperature, time, solvent, etc.), as well as solubility, bioavailability, structural, and thermal stability data. The results and description of characterization techniques to determine the structural modifications resulting from transforming a pure crystalline API into a co-crystal, polymorph, or co-amorphous system are presented. Additionally, the characterization methodologies and results of intermolecular interactions induced by mechanical activation are discussed to explain the properties of the pharmaceutical formulations obtained after the ball milling process.

Prediction and Preparation of Coamorphous Phases of a Bislactam

The effectiveness of a partial least squares-discriminant analysis coamorphous prediction model was tested using coamorphous screening data for a promising coamorphous former, the dimer of N-vinyl(caprolactam) (bisVCap) with a range of active pharmaceutical ingredients. The prediction model predicted 71% of the systems correctly. An experimental coamorphous screen was performed with this coformer with 13 different active pharmaceutical ingredients, and the results were compared to the predictions from the model. A total of 85% of the systems were correctly predicted. Stability assessments of three coamorphous systems showed that the prediction model score did not strongly correlate with the stability of the coamorphous material. The model performed well with small-molecule coformers, such as bisVCap, despite the difference in structure and properties compared to the amino-acid-based model training set.

Benchmarking the Solubility Enhancement and Storage Stability of Amorphous Drug–Polyelectrolyte Nanoplex against Co-Amorphous Formulation of the Same Drug

Amorphization, typically in the form of amorphous solid dispersion (ASD), represents a well-established solubility enhancement strategy for poorly soluble drugs. Recently, two amorphous drug formulations, i.e., the amorphous drug–polyelectrolyte nanoparticle complex (nanoplex) and co-amorphous system, have emerged as promising alternatives to circumvent the issues faced by ASD (i.e., large dosage requirement, high hygroscopicity). In the present work, the nanoplex was benchmarked against the co-amorphous system in terms of the preparation efficiency, drug payload, thermal stability, dissolution rate, supersaturation generation, and accelerated storage stability. Weakly acidic curcumin (CUR) and weakly basic ciprofloxacin (CIP) were used as the model poorly soluble drugs. The CUR and CIP nanoplexes were prepared using chitosan and sodium dextran sulfate as the polyelectrolytes, respectively. The co-amorphous CUR and CIP were prepared using tannic acid and tryptophan as the co-formers, respectively. The benchmarking results showed that the amorphous drug nanoplex performed as well as, if not better than, the co-amorphous system depending on the drug in question and the aspects being compared. The present work successfully established the nanoplex as an equally viable amorphous drug formulation as the more widely studied co-amorphous system to potentially serve as an alternative to ASD.

Design of a Stable Coamorphous System Using Lactose as an Antiplasticizing Agent for Diphenhydramine Hydrochloride with a Low Glass Transition Temperature

Coamorphous systems comprising small molecules are emerging as counterparts to polymeric solid dispersions. However, the glass transition temperatures (T_gs) of coamorphous materials are relatively low because of the lack of polymeric carriers with higher T_gs. This study aimed to investigate the applicability of lactose (LAC) as an antiplasticizing coformer to a coamorphous system. Diphenhydramine hydrochloride (DPH) was selected as a model drug (T_g = 16 °C). Differential scanning calorimetry showed a comelting point in addition to a decrease in the neat melting points depending on the composition of the physical mixtures, suggesting that the mixture of DPH-LAC was eutectic. The melting point of the eutectic mixture was calculated according to the Schröder-van Laar equation. The heat of fusion of the eutectic mixture was maximized at a 70:30 molar ratio of DPH to LAC; at this point, the melting peaks of the pure components disappeared. The heat flow profiles following the melting and cooling of DPH-LAC physical mixtures at the ratios from 10:90 to 90:10 showed a single T_g, suggesting the formation of a coamorphous system. Lactose showed a T_g of over 100 °C, and the T_g of DPH increased with the molar ratio of LAC; it was 84 °C at a 10:90 molar ratio of DPH to LAC. The Raman image indicated the formation of a homogeneous dispersion of DPH and LAC in the coamorphous system. Peak shifts in the infrared spectra indicated the presence of intermolecular interactions between the amino group of DPH and the hydroxyl group of LAC. Principal component analysis of the infrared spectra revealed a significant change at the 70:30 molar ratio of DPH to LAC, which was in agreement with the results of the thermal analysis. A stability test at 40 °C revealed rapid crystallization of the supercooled liquid DPH. The coamorphous samples containing 10-50% of LAC remained in an amorphous state for 21 days, and no crystallization was observed for the samples containing >60% of LAC for 28 days. The relatively lower T_g (less than 40 °C) of the coamorphous system containing 10-50% of LAC might have caused crystallization during storage. These findings indicate that LAC, which is a safe and widely used pharmaceutical excipient, can be applied to coamorphous systems as an antiplasticizing coformer.

Sustained Release of Co-Amorphous Matrine-Type Alkaloids and Resveratrol with Anti-COVID-19 Potential

Matrine (MAR), oxymatrine (OMAR), and sophoridine (SPD) are natural alkaloids with varying biological activities; matrine was recently used for the treatment of coronavirus disease 2019 (COVID-19). However, the short half-lives and rapid elimination of these matrine-type alkaloids would lead to low oral bioavailability and serious side effects. Herein, resveratrol (RES) was selected as a co-former to prepare their co-amorphous systems to improve the therapeutic index. The formation of co-amorphous MAR-RES, OMAR-RES, and SPD-RES was established through powder X-ray diffraction and modulated temperature differential scanning calorimetry. Furthermore, Fourier transform infrared spectroscopy and NMR studies revealed the strong molecular interactions between resveratrol and these alkaloids, especially OMAR-RES. Matrine, oxymatrine, and sophoridine in the co-amorphous systems showed sustained release behaviors in the dissolution experiments, due to the recrystallization of resveratrol on the surface of co-amorphous drugs. The three co-amorphous systems exhibited excellent physicochemical stability under high relative humidity conditions. Our study not only showed that minor structural changes of active pharmaceutical ingredients may have distinct molecular interactions with the co-former, but also discovered a new type of sustained release mechanism for co-amorphous drugs. This promising co-amorphous drug approach may present a unique opportunity for repurposing these very promising drugs against COVID-19.

Impact of Molecular Surface Diffusion on the Physical Stability of Co-Amorphous Systems

In this study, surface diffusion of l-aspartic acid-carvedilol (ASP-CAR) co-amorphous systems at different ASP concentrations is measured and correlated with their physical stability. ASP-CAR films at ASP concentrations of 1-5% (w/w) were prepared by a newly developed method based on a vacuum compression molding process. Surface diffusion measurements were conducted on these systems based on the surface grating decay method using atomic force microscopy (AFM). The results demonstrate that a small amount of ASP (i.e., ≤ 5% w/w) in the co-amorphous systems could significantly slow down the grating decay process compared with that of pure amorphous CAR, indicating a reduced surface diffusion of CAR molecules. The decay time gradually increased in co-amorphous systems with increasing ASP concentration from 1 to 5% (w/w), with the longest observed decay time of around 800 h for the 5%ASP-CAR system, which was more than 200 times longer compared to the decay time of pure amorphous CAR (approximately 3 h). A good correlation between the decay constants of the pure amorphous CAR and co-amorphous films at ASP concentrations of 1-5% (w/w) and the physical stability of corresponding amorphous powder samples was found. Overall, this study provides a new method to prepare co-amorphous films for surface property measurements and reveals the impact of surface diffusion on the physical stability of co-amorphous systems.

Self-gelation involved in the transformation of resveratrol and piperine from a co-amorphous system into a co-crystal system

Self-gelation of co-amorphous system promotes the transformation into its co-crystal system during dissolution.

Mechanistic insight into gel-induced aggregation of amorphous curcumin during dissolution process

Amorphous curcumin (CUR) exhibited a decreased dissolution rate in comparison with the crystalline counterpart due to its gel formation during dissolution. The main purpose of the present study is to explore the mechanism of such gelation phenomenon. It was found that the dissolution of amorphous CUR and gel properties were influenced by the temperature and pH of the media. The formed gels were characterized by TPA, SEM, DSC, XRPD, FTIR and PLM. The results indicated that the gelation process led to the formation of a porous structure in which water molecules infiltrate, and entered into its supercooled liquid state with high viscosity when contacting aqueous media, accompanied by decreased T_g and crystalline transformation. In addition, mixing with hydrophilic excipients (such as hydrophilic silica) accelerated the gel formation of amorphous CUR, while the addition of hydrophobic excipients (such as hydrophobic silica and magnesium stearate) could effectively weaken and even eliminate the gelation, hence significantly improving its dissolution. Furthermore, according to contact angle measurement and fluorescence microscope observation, hydrophilic excipients were found to be able to accelerate water entering into the interior of amorphous CUR, hence facilitating the gelation, while hydrophobic excipients would hinder water infiltration into the powder and thus achieve degelation. In conclusion, it is important to recognize that the gelation potential of some amorphous materials should be considered in developing robust amorphous drug product of high quality and performance.