Co-Amorphous Formation of High-Dose Zwitterionic Compounds with Amino Acids To Improve Solubility and Enable Parenteral Delivery

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.

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.Communicated by Ramaswamy H. Sarma.

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

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

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.

Non-salt based co-amorphous formulation produced by freeze-drying

Amino acids-based co-amorphous system (CAM) has shown to be a promising approach to overcome the dissolution challenge of biopharmaceutics classification system class II drugs. To date, most CAM formulations are based on salt formation at a 1:1 M ratio and are prepared by mechanical activation. However, its use in medicinal products is still limited due to the lack of in-depth understanding of non-ionic based molecular interactions. There are also limited studies on the effect of drug-to-co-former ratio, the development of more scalable, less aggressive, manufacturing processes such as freeze drying and its dissolution benefits. This work aims to investigate the effect of the ratio of tryptophan (a model non-ionic amino acid) to indomethacin (a model drug) on a non-salt-based CAM prepared via freeze-drying with the tert-butyl alcohol-water cosolvent system. The CAM material was systemically characterized at various stages of the freeze-drying process using DSC, UV-Vis, FT-IR, NMR, TGA and XRPD. Dissolution performance and physical stability upon storage were also investigated. Freeze-drying using the cosolvent system has been successfully shown to produce CAMs. The molecular interactions involving H-bonding, H/π and π-π between compounds have been confirmed by FT-IR and NMR. The drug release rate for formulations with a 1.5:1 drug: amino acid molar ratio (or 1:0.42 wt ratio) or below is found to be significantly improved compared to the pure crystalline drug. Furthermore, formulation with a 2.3:1 drug:amino acid molar ratio (or 1:0.25 wt ratio) or below have shown to be physically stable for at least 9 months when stored at dry condition (5% relative humidity, 25 °C) compared to the pure amorphous indomethacin. We have demonstrated the potential of freeze-drying using tert-butyl alcohol-water cosolvent system to produce an optimal non-salt-based class II drug-amino acid CAM.

Current Techniques of Water Solubility Improvement for Antioxidant Compounds and Their Correlation with Its Activity: Molecular Pharmaceutics

The aqueous solubility of a drug is important in the oral formulation because the drug can be absorbed from intestinal sites after being dissolved in the gastrointestinal fluid, leading to its bioavailability. Almost 80% of active pharmaceutical ingredients are poorly water-soluble, including antioxidant compounds. This makes antioxidant activity inefficient in preventing disease, particularly for orally administered formulations. Although several investigations have been carried out to improve the solubility of antioxidant compounds, there is still limited research fully discussing the subject. Therefore, this study aimed to provide an overview and discussion of the issues related to the methods that have been used to improve the solubility and activity of antioxidant compounds. Articles were found using the keywords "antioxidant" and "water solubility improvement" in the Scopus, PubMed, and Google Scholar databases. The selected articles were published within the last five years to ensure all information was up-to-date with the same objectives. The most popular methods of the strategies employed were solid dispersion, co-amorphous, and nanoparticle drug delivery systems, which were used to enhance the solubility of antioxidant compounds. These investigations produced impressive results, with a detailed discussion of the mechanism of improvement in the solubility and antioxidant activity of the compounds developed. This review shows that the strategies used to increase the solubility of antioxidant compounds successfully improved their antioxidant activity with enhanced free radical scavenging abilities.

Co-amorphous Systems of Sinomenine with Platensimycin or Sulfasalazine: Physical Stability and Excipient-Adjusted Release Behavior

There is strong interest to develop affordable treatments for the infection-associated rheumatoid arthritis (RA). Here, we present a drug-drug co-amorphous strategy against RA and the associated bacterial infection by the preparation and characterization of two co-amorphous systems of sinomenine (SIN) with platensimycin (PTM) or sulfasalazine (SULF), two potent antibiotics. Both of them were comprehensively characterized using powder X-ray diffraction, temperature-modulated differential scanning calorimetry, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The co-amorphous forms of SIN-PTM and SIN-SULF exhibited high T_gs at 139.10 ± 1.0 and 153.3 ± 0.2 °C, respectively. After 6 months of accelerated tests and 1 month of drug-excipient compatibility experiments, two co-amorphous systems displayed satisfactory physical stability. The formation of salt and strong intermolecular interactions between SIN and PTM or SULF, as well as the decreased molecular mobility in co-amorphous systems, may be the intrinsic mechanisms underlying the excellent physical stability of both co-amorphous systems. In dissolution tests, two co-amorphous systems displayed distinct reduced SIN-accumulative releases (below 20% after 6 h of release experiments), which may lead to its poor therapeutic effect. Hence, we demonstrated a controlled release strategy for SIN by the addition of a small percentage of polymers and a small-molecule surfactant to these two co-amorphous samples as convenient drug excipients, which may also be used to improve the unsatisfactory dissolution behaviors of the previously reported SIN co-amorphous systems. Several hydrogen bonding interactions between SIN and PTM or SULF could be identified in NMR experiments in DMSO-d₆, which may be underlying reasons of decreased dissolution behaviors of both co-amorphous forms. These drug-drug co-amorphous systems could be a potential strategy for the treatment of infection-associated RA.

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.

Mechanistic study of the solubilization effect of basic amino acids on a poorly water-soluble drug

Amino acids have shown promising abilities to form complexes with poorly water-soluble drugs and improve their physicochemical properties for a better dissolution profile through molecular interactions. Salt formation via ionization between acidic drugs and basic amino acids is known as the major contributor to solubility enhancement. However, the mechanism of solubility enhancement due to non-ionic interactions, which is less pH-dependent, remains unclear. The aim of this study is to evaluate non-ionic interactions between a model acidic drug, indomethacin (IND), and basic amino acids, arginine, lysine and histidine, in water. At low concentrations of amino acids, IND-arginine and IND-lysine complexes have shown a linear relationship (A_L-type phase solubility diagram) between IND solubility and amino acid concentration, producing ∼1 : 1 stoichiometry of drug-amino acid complexes as expected due to the strong electrostatic interactions. However, IND-histidine complexes have shown a nonlinear relationship with lower improvement in IND solubility due to the weaker electrostatic interactions when compared to arginine and lysine. Interestingly, the results have also shown that at high arginine concentrations, the linearity was lost between IND solubility and amino acid concentration with a negative diversion from linearity, following the type-A_N phase solubility. This is indicative that the electrostatic interaction is being interrupted by non-electrostatic interactions, as seen with histidine. The IND-lysine complex, on the other hand, showed a complex curvature phase solubility diagram (type B_S) as lysine self-assembles and polymerizes at higher concentrations. The freeze-dried drug-amino acid solids were further characterized using thermal analysis and infrared spectroscopy, with results showing the involvement of weak non-ionic interactions. This study shows that the solubility improvement of an insoluble drug in the presence of basic amino acids was due to both non-ionic and ionic interactions.

Co-Amorphous Formation of Simvastatin-Ezetimibe: Enhanced Physical Stability, Bioavailability and Cholesterol-Lowering Effects in LDLr-/-Mice

Hypercholesterolemia is one of the independent risk factors for the development of cardiovascular diseases such as atherosclerosis. The treatment of hypercholesterolemia is of great significance to reduce clinical cardiovascular events and patient mortality. Simvastatin (SIM) and ezetimibe (EZE) are commonly used clinically as cholesterol-lowering drugs; however, their treatment efficacy is severely affected by their poor water solubility and low bioavailability. In this study, SIM and EZE were made into a co-amorphous system to improve their dissolution, oral bioavailability, storage stability, and cholesterol-lowering effects. The SIM-EZE co-amorphous solids (CO) were prepared successfully using the melt-quenched technique, and the physicochemical properties of CO were characterized accordingly, which exhibited improved physical stability and faster dissolution release profiles than their physical mixture (PM). In the pharmacokinetic study, the SIM-EZE CO or PM was given once by oral gavage, and mouse blood samples were collected retro-orbitally at multiple time points to determine the plasma drug concentrations. In the pharmacodynamic study, low-density lipoprotein receptor-deficient (LDLr−/−) mice were fed with a high-fat diet (HFD) for two weeks to establish a mouse model of hypercholesterolemia. Using PM as a control, we investigated the regulation of CO on plasma lipid levels in mice. Furthermore, the mice feces were collected to determine the cholesterol contents. Besides, the effect of EZE on the NPC1L1 mRNA expression level in the mouse intestines was also investigated. The pharmacokinetics results showed that the SIM-EZE CO has improved bioavailability compared to the PM. The pharmacodynamic studies showed that SIM-EZE CO significantly increased the cholesterol-lowering effects of the drugs compared to their PM. The total cholesterol excretion in the mouse feces and inhibitory effect on NCP1L1 gene expression in the mouse intestines after being given the SIM-EZE CO were more dramatic than the PM. Our study shows that the SIM-EZE CO prepared by the melt-quenched method can significantly improve the stability, bioavailability, and cholesterol-lowering efficacy with excellent development potential as a new drug formulation.

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.

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.

Ball milling and hot-melt extrusion of indomethacin-L-arginine-vinylpyrrolidone-vinyl acetate copolymer: Solid-state properties and dissolution performance

Commonly applied approaches to enhance the dissolution properties of low water-soluble crystalline active pharmaceutical ingredients (APIs) include their amorphization by incorporation into a polymeric matrix and the formation of amorphous solid dispersions (ASDs), or blending APIs with low-molecular-weight excipients and the formation of a co-amorphous system. This study focused on the preparation and characterization of binary (consisting of indomethacin (IND) and polymer - copovidone (PVP VA 64), as a carrier, or amino acid - L-arginine (ARG), as a co-former) and ternary (comprising the same API, polymer, and amino acid) formulations. Formulations were produced by ball milling (BM) and/or hot-melt extrusion (HME), and extensive physicochemical characterization was performed. Specifically, the physicochemical and solid-state properties of a model IND-ARG system incorporated into a polymeric matrix of PVP VA 64 by HME and BM as well as by combined BM/HME method together with the impact of the preparation strategy on the dissolution profiles and long-term physical stability were investigated. Ball-milled binary and ternary formulations were found to be amorphous. The residual crystals corresponding to IND-ARG salt were identified in the ternary formulations produced via HME. Despite the presence of a crystalline phase, dissolution tests showed that ternary systems prepared by HME exhibited improved IND solubility when compared to pure crystalline IND and their corresponding physical mixture. None of the binary and ternary formulations that were initially fully amorphous did undergo recrystallization during the entire period of preservation (minimum of 12 months) in dry conditions at 25℃.

[Construction of Coamorphous Technology Aimed at Improving Membrane Permeability and Application to Emulsion]

The coamorphous formation between naringenin (NRG) and hesperetin (HPT) was investigated with the aim of enhancing their solubility and membrane permeability. In addition, application to emulsion of coamorphous was investigated. The melt-quenched particles (MQPs) of NRG and HPT were prepared in a range of molar ratios of NRG/HPT (3/1 to 1/3). All MQPs showed the amorphous state and single glass transition temperature. MQPs of NRG/HPT (1/1) could kept the amorphous state under storage. On the other hand, other MQPs recrystallized from the compound with a higher molar ratio. These results indicated that NRG and HPT formed the coamorphous at a molar ratio of 1 to 1. The coamorphous formation enhanced the apparent solubilities of NRG and HPT in aqueous media. Furthermore, MQPs of NRG/HPT (1/1) increased a permeated amount of NRG and HPT via the synthetic membrane in Franz Cell. When the solubility of NRG and HPT in oil components were investigated, the MQPs of NRG/HPT (1/1) enhanced the solubility of both compounds. This study highlighted the importance of coamorphous formation as a formulation to enhance solubility in oil components and aqueous media, and membrane permeability of both NRG and HPT.

Deaggregation and Crystallization Inhibition by Small Amount of Polymer Addition for a Co-Amorphous Curcumin-Magnolol System

Different from previously reported co-amorphous systems, a co-amorphous curcumin-magnolol (CUR-MAG CM) system, as compared with its crystalline counterparts, exhibited decreased dissolution due to its aggregation during dissolution. The main purpose of the present study is to deaggregate CUR-MAG CM to optimize drug dissolution and explore the deaggregation mechanism involved. Herein, a small amount of polymer (HPMC, HPC, and PVP K30) was co-formulated at 5% (w/w) with CUR-MAG CM as ternary co-amorphous systems. The polymer addition changed the surface properties of CUR-MAG CM including improved water wettability enhanced surface free energy, and hence exerted a deaggregating effect. As a result, the ternary co-amorphous systems showed faster and higher dissolution as compared with crystalline CUR/MAG and CUR-MAG CM. In addition, the nucleation and crystal growth of dissolved CUR and MAG molecules were significantly inhibited by the added polymer, maintaining a supersaturated concentration for a long time. Furthermore, polymer addition increased the T_g of CUR-MAG CM, potentially involving molecular interactions and inhibiting molecular mobility, resulting in enhanced physical stability under 25 °C/60% RH and 40 °C/75% RH conditions. Therefore, this study provides a promising strategy to optimize the dissolution and physical stability of co-amorphous systems by deaggregation and crystallization inhibition via adding small amounts of polymers.

Recent Technologies for Amorphization of Poorly Water-Soluble Drugs

Amorphization technology has been the subject of continuous attention in the pharmaceutical industry, as a means to enhance the solubility of poorly water-soluble drugs. Being in a high energy state, amorphous formulations generally display significantly increased apparent solubility as compared to their crystalline counterparts, which may allow them to generate a supersaturated state in the gastrointestinal tract and in turn, improve the bioavailability. Conventionally, hydrophilic polymers have been used as carriers, in which the amorphous drugs were dispersed and stabilized to form polymeric amorphous solid dispersions. However, the technique had its limitations, some of which include the need for a large number of carriers, the tendency to recrystallize during storage, and the possibility of thermal decomposition of the drug during preparation. Therefore, emerging amorphization technologies have focused on the investigation of novel amorphous-stabilizing carriers and preparation methods that can improve the drug loading and the degree of amorphization. This review highlights the recent pharmaceutical approaches utilizing drug amorphization, such as co-amorphous systems, mesoporous particle-based techniques, and in situ amorphization. Recent updates on these technologies in the last five years are discussed with a focus on their characteristics and commercial potential.

Recent solubility and dissolution enhancement techniques for repaglinide a BCS class II drug: a review

Repaglinide is an oral blood-glucose-lowering drug used to manage type-2 diabetes mellitus by lowering post-prandial glucose by stimulating insulin secretion from pancreatic beta cells.

According to the biopharmaceutical classification system, repaglinide falls under the class II category. For such drugs, limited solubility and poor dissolution rate are the major hurdles to overcome by formulation scientists, as they hinder drug absorption and lead to inadequate therapeutic effects.

Therefore, this review aims to discuss in depth the various approaches investigated in the past five years to improve the solubility and dissolution of orally administered repaglinide: namely, solid dispersion, co-amorphous technology, cyclodextrin complexation, phospholipid complexes and polymeric micelles, nanocrystals, nanosuspensions and nanofibers.

Influence of Lactobacillus Biosurfactants on Skin Permeation of Hydrocortisone

One of the most widely used strategies to improve drug diffusion through the skin is the use of permeation enhancers. The aim of this work was to investigate the effect of two biosurfactants (BS), produced by Lactobacillus crispatus BC1 and Lactobacillus gasseri BC9, on the skin permeation profile of hydrocortisone (HC, model drug). HC aqueous solubility and in vitro diffusion studies through porcine skin were performed in the presence of BC1-BS and BC9-BS at concentrations below and above critical micellar concentrations (CMC). Moreover, skin hydration tests and differential scanning calorimetry (DSC) analysis were performed to further investigate BS interaction with the outermost layer of the skin. Both BS increased HC solubility, especially at concentrations above their CMC. At concentrations below the CMC, drug permeation through the skin was improved, as the result of a dual effect: a) the formation of a superficial lipophilic environment, as confirmed by the reduction in skin hydration and b) the interaction between BS and the stratum corneum (SC), as demonstrated by the DSC curves. From the obtained data, it appears that BC1-BS and BC9-BS could represent new promising green excipients for drug permeation enhancement through the skin.

Co-Amorphous Drug Formulations in Numbers: Recent Advances in Co-Amorphous Drug Formulations with Focus on Co-Formability, Molar Ratio, Preparation Methods, Physical Stability, In Vitro and In Vivo Performance, and New Formulation Strategies

Co-amorphous drug delivery systems (CAMS) are characterized by the combination of two or more (initially crystalline) low molecular weight components that form a homogeneous single-phase amorphous system. Over the past decades, CAMS have been widely investigated as a promising approach to address the challenge of low water solubility of many active pharmaceutical ingredients. Most of the studies on CAMS were performed on a case-by-case basis, and only a few systematic studies are available. A quantitative analysis of the literature on CAMS under certain aspects highlights not only which aspects have been of great interest, but also which future developments are necessary to expand this research field. This review provides a comprehensive updated overview on the current published work on CAMS using a quantitative approach, focusing on three critical quality attributes of CAMS, i.e., co-formability, physical stability, and dissolution performance. Specifically, co-formability, molar ratio of drug and co-former, preparation methods, physical stability, and in vitro and in vivo performance were covered. For each aspect, a quantitative assessment on the current status was performed, allowing both recent advances and remaining research gaps to be identified. Furthermore, novel research aspects such as the design of ternary CAMS are discussed.

Insights into co-amorphous systems in therapeutic drug delivery

Co-amorphous (CAM) systems are promising drug-delivery systems in the arena of therapeutic drug delivery, addressing the poor aqueous solubility of drugs by enhancing solubility and thereby improving the oral bioavailability and therapeutic effect of the drug. A CAM system is a single-phase homogeneous blend of two or more low molecular weight molecules that can be drug–drug or drug–co-former, stabilized via intermolecular interactions, adding the benefit of thermodynamic stability. This review covers the fundamentals of CAM systems and recent advances in formulation development. In particular, we strive to address the theoretical, molecular, technical and biopharmaceutical aspects, advantages over polymeric amorphous solid dispersions, mechanisms of stabilization of amorphous forms, insights into unexplored in silico tools in excipient selection and regulatory viewpoints.

A Multivariate Approach for the Determination of the Optimal Mixing Ratio of the Non-Strong Interacting Co-Amorphous System Carvedilol-Tryptophan

Converting crystalline compounds into co-amorphous systems is an effective way to improve the solubility of poorly water-soluble drugs. It is, however, of critical importance for the physical stability of co-amorphous systems to find the optimal mixing ratio of the drug with the co-former. In this study, a novel approach for this challenge is presented, exemplified with the co-amorphous system carvedilol–tryptophan (CAR–TRP). Following X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC) of the ball-milled samples to confirm their amorphous form, Fourier-transform infrared spectroscopy (FTIR) and principal component analysis (PCA) were applied to investigate intermolecular interactions. A clear deviation from a purely additive spectrum of CAR and TRP was visualized in the PCA score plot, with a maximum at around 30% drug (mol/mol). This deviation was attributed to hydrogen bonds of CAR with TRP ether groups. The sample containing 30% drug (mol/mol) was also the most stable sample during a stability test. Using the combination of FTIR with PCA is an effective approach to investigate the optimal mixing ratio of non-strong interacting co-amorphous systems.

Triple Strategies to Improve Oral Bioavailability by Fabricating Coamorphous Forms of Ursolic Acid with Piperine: Enhancing Water-Solubility, Permeability, and Inhibiting Cytochrome P450 Isozymes

As a BCS IV drug, ursolic acid (UA) has low oral bioavailability mainly because of its poor aqueous solubility/dissolution, poor permeability, and metabolism by cytochrome P450 (CYP) isozymes, such as CYP3A4. Most UA preparations demonstrated a much higher dissolution than that of its crystalline form yet a low drug concentration in plasma due to their lower consideration or evaluation for the permeability and metabolism issues. In the current study, a supramolecular coamorphous system of UA with piperine (PIP) was prepared and characterized by powder X-ray diffraction, differential scanning calorimetry, and scanning electron microscopy. In comparison to crystalline UA and UA in physical mixture, such coamorphous system enhanced solubility (5.3-7-fold in the physiological solution) and dissolution (7-8-fold in the physiological solution within 2 h) of UA and exhibited excellent physical stability under 90-day storage conditions. More importantly, the pharmacokinetic study of coamorphous UA in rats exhibited 5.8-fold and 2.47-fold improvement in AUC0-∞ value, respectively, compared with its free and mixed crystalline counterparts. In order to further explore the mechanism of such improvement, the molecular interactions of a coamorphous system in the solid state were investigated. Fourier transform infrared spectroscopy, solid-state 13C nuclear magnetic resonance spectroscopy, and density functional theory modeling suggested that intermolecular hydrogen bonds with strong interactions newly formed between UA and PIP after coamorphization. The in vitro permeability studies across Caco-2 cell monolayer and metabolism studies by rat hepatic microsomes indicated that free PIP significantly increased the permeability of UA and inhibited the enzymatic metabolism of UA by CYP3A4. However, PIP in the coamorphous combination exhibited a much lower level in the bioenhancing than its free form arising from the synchronized dissolution characteristic of the preparation (only 60% of PIP released in comparison to its free counterpart in 2 h). The in situ loop study in rats proposed that the acid-sensitive dissolution in the stomach of the coamorphous preparation helped to improve the effective free drug concentration, thereby facilitating PIP to play its role in bioenhancing. The current study offers an exploratory strategy to overcome poor solubility/dissolution, poor permeability, and metabolism by cytochrome P450 isozymes of the BCS IV drug to improve its oral bioavailability.

Amorphous systems for delivery of nutraceuticals: challenges opportunities

Amorphous solid products have recently gained a lot of attention as key solutions to improve the solubility and bioavailability of poorly soluble nutraceuticals. A pure amorphous drug is a high-energy form; physically/chemically unstable and so easily gets recrystallized into the less soluble crystalline form limiting solubility and bioavailability issues. Amorphous solid dispersion and co-amorphous are new formulation approach that stabilized unstable amorphous form through different mechanisms such as preventing mobility, high glass transition temperature and molecular interaction. Nutraceuticals have been received the utmost importance due to their health benefits. However, most of these compounds have been associated with poor oral bioavailability due to poor solubility, high lipophilicity, high melting point, poor permeability, degradability and rapid metabolism in the gastrointestinal tract (GIT) which limits its health benefits. This review provides us a systematic application of amorphous systems to the delivery of poorly soluble nutraceuticals, with the aim of overcoming their pharmacokinetic limitations and improved pharmacological potential. In particular, it describes the challenges associated with delivery of oral nutraceuticals, various methods involved in the preparation and characterization of amorphous systems and permeability enhancement of nutraceuticals are in detail.

Preparation of Co-Amorphous Systems by Freeze-Drying

Freeze-drying was evaluated as a production technique for co-amorphous systems of a poorly water-soluble drug. Naproxen was freeze-dried together with arginine and lysine as co-former. To increase the solubility of naproxen in the starting solution, the applicability of five surfactants was investigated, namely sodium dodecyl sulfate, pluronic F-127, polyoxyethylene (40) stearate, tween 20 and TPGS 1000. The influence of the surfactant type, surfactant concentration and total solid content to be freeze-dried on the solid state of the sample was investigated. X-ray powder diffraction and differential scanning calorimetry showed that the majority of systems formed co-amorphous one-phase systems. However, at higher surfactant concentrations, and depending on the surfactant type, surfactant reflections were observed in the XRPD analysis upon production. Crystallization of both naproxen and amino acid occurred from some combinations under storage. In conclusion, freeze-drying was shown to be a feasible technique for the production of a selection of co-amorphous drug–amino acid formulations.

Production and Characterization of Anti-Inflammatory Monascus Pigment Derivatives

The prevention and treatment of chronic inflammation using food-derived compounds are desirable from the perspectives of marketing and safety. Monascus pigments, widely used as food additives, can be used as a chronic inflammation treatment. Orange Monascus pigments were produced by submerged fermentation in a 5 L bioreactor, and multiple orange Monascus pigment derivatives with anti-inflammatory activities were synthesized using aminophilic reaction. A total of 41 types of pigment derivatives were produced by incorporating amines and amino acids into the orange pigments. One derivative candidate that inhibited nitric oxide (NO) production in Raw 264.7 cells and exhibited low cell cytotoxicity was identified via in vitro assay. The 2-amino-4 picoline derivative inhibited NO production of 48.4%, and exhibited cell viability of 90.6%. Expression of inducible NO synthase, an important enzyme in the NO synthesis pathway, was suppressed by such a derivative in a dose-dependent manner. Therefore, this derivative has potential as a functional food colorant with anti-inflammatory effects.

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

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

Fragment-based design of small molecule PCSK9 inhibitors using simulated annealing of chemical potential simulations

PCSK9 is a protein secreted by the liver that binds to the low-density lipoprotein receptor (LDLR), causing LDLR internalization, decreasing the clearance of circulating LDL particles. Mutations in PCSK9 that strengthen its interactions with LDLR result in familial hypercholesterolemia (FH) and early onset atherosclerosis, while nonsense mutations of PCSK9 result in cardio-protective hypocholesterolemia. These observations led to PCSK9 inhibition for cholesterol lowering becoming a high-interest therapeutic target, with antibody drugs reaching the market. An orally-available small molecule drug is highly desirable, but inhibiting the PCSK9/LDLR protein-protein interaction (PPI) has proven challenging. Alternate approaches to finding good lead candidates are needed. Motivated by the FH mutation data on PCSK9, we found that modeling the PCSK9/LDLR interface revealed extensive electron delocalization between and within the protein partners. Based on this, we hypothesized that compounds assembled from chemical fragments could achieve the affinity required to inhibit the PCSK9/LDLR PPI if they were selected to interact with PCSK9 in a way that, like LDLR, also involves significant fractional charge transfer to form partially covalent bonds. To identify such fragments, Simulated Annealing of Chemical Potential (SACP) fragment simulations were run on multiple PCSK9 structures, using optimized partial charges for the protein. We designed a small molecule, composed of several fragments, predicted to interact at two sites on the PCSK9. This compound inhibits the PPI with 1 μM affinity. Further, we designed two similar small molecules where one allows charge delocalization though a linker and the other doesn’t. The first inhibitor with charge delocalization enhances LDLR surface expression by 60% at 10 nM, two orders of magnitude more potent than the EGF domain of LDLR. The other enhances LDLR expression by only 50% at 1 μM. This supports our conjecture that fragments can have surprisingly outsized efficacy in breaking PPI’s by achieving fractional charge transfer leading to partially covalent bonding.

Preparation of Amorphous Composite Particles of Drugs with Ursodeoxycholic Acid as Preclinical Formulations

We studied the possibility of using ursodeoxycholic acid (UDCA) as an excipient to create an amorphous composite that can be administered to animals in preclinical studies of experimental drugs. Three UDCA-based amorphous samples composed of nifedipine (NIF), indomethacin (IND), and naproxen (NAP) were found by screening. The UDCA-based formulations were adjudged amorphous by solid-state analysis using X-ray powder diffraction and differential scanning calorimetry. In addition, amorphous samples of NIF-UDCA, IND-UDCA, and NAP-UDCA did not crystallize while in 1% methyl cellulose (MC) solution for 120 min, although an amorphous solid dispersion of NIF-poly(vinylpyrrolidone) (PVP) crystallized rapidly. The low hygroscopicity of UDCA helps NIF maintain an amorphous state in 1% MC solution. The UDCA-based amorphous composites can be administered as suspended formulations to animals in preclinical studies.

Involvement of metabolism-permeability in enhancing the oral bioavailability of curcumin in excipient-free solid dispersions co-formed with piperine

Curcumin (CUR) has gained increasing interest worldwide due to multiple biological activities. However, the therapeutic application remains limited because of its low aqueous solubility, intestinal metabolism and poor membrane permeability. In present study, an excipient-free CUR solid dispersion co-formed with piperine (PIP), the absorption enhancer involving metabolism-permeability, was successfully prepared by melting and quench cooling (co-amorphous CUR-PIP). The co-amorphous CUR-PIP exhibited superior performance in non-sink dissolution compared with crystalline and amorphous CUR, and showed physically stable at least 3 months, attributing to the strong molecular interactions between CUR and PIP as evaluated by FTIR spectra. Furthermore, the combination of PIP with CUR in the co-amorphous formulation could inhibit the glucuronidation of CUR, as exhibited in the in vitro assay of rat intestinal microsomes. The co-amorphous CUR-PIP would also exhibit higher gastrointestinal membrane permeability of CUR, as confirmed by P_app of CUR in Caco-2 model. After administration of co-amorphous CUR-PIP, the AUC of CUR significantly increased by 2.16- and 1.92-fold those in crystalline and amorphous CUR, respectively. This study demonstrates that the developed co-amorphous CUR-PIP can enhance the bioavailability of CUR by increasing its dissolution, inhibiting metabolic processes, and facilitating membrane permeability.

Advances in coamorphous drug delivery systems

In recent years, the coamorphous drug delivery system has been established as a promising formulation approach for delivering poorly water-soluble drugs. The coamorphous solid is a single-phase system containing an active pharmaceutical ingredient (API) and other low molecular weight molecules that might be pharmacologically relevant APIs or excipients. These formulations exhibit considerable advantages over neat crystalline or amorphous material, including improved physical stability, dissolution profiles, and potentially enhanced therapeutic efficacy. This review provides a comprehensive overview of coamorphous drug delivery systems from the perspectives of preparation, physicochemical characteristics, physical stability, in vitro and in vivo performance. Furthermore, the challenges and strategies in developing robust coamorphous drug products of high quality and performance are briefly discussed.

Co-Amorphous Solid Dispersions for Solubility and Absorption Improvement of Drugs: Composition, Preparation, Characterization and Formulations for Oral Delivery

The amorphous solid state offers an improved apparent solubility and dissolution rate. However, due to thermodynamic instability and recrystallization tendencies during processing, storage and dissolution, their potential application is limited. For this reason, the production of amorphous drugs with adequate stability remains a major challenge and formulation strategies based on solid molecular dispersions are being exploited. Co-amorphous systems are a new formulation approach where the amorphous drug is stabilized through strong intermolecular interactions by a low molecular co-former. This review covers several topics applicable to co-amorphous drug delivery systems. In particular, it describes recent advances in the co-amorphous composition, preparation and solid-state characterization, as well as improvements of dissolution performance and absorption are detailed. Examples of drug-drug, drug-carboxylic acid and drug-amino acid co-amorphous dispersions interacting via hydrogen bonding, π−π interactions and ionic forces, are presented together with corresponding final dosage forms.