Influence of variation in molar ratio on co-amorphous drug-amino acid systems

Leveraging Molecular Interactions to Develop a Generalized Design Framework for Coamorphous Drug-Drug Mixtures Exhibiting Elevated Glass Transition Temperatures

Coamorphous mixtures (CAMs) prepared with two drugs have the potential to enhance the oral absorption of poorly soluble drugs and achieve combination therapy. From a practical standpoint, improving the glass transition temperature (Tg) of CAMs is desirable as it enhances stability and extends shelf life during storage. Toward the eventual goal of developing highly stable CAMs, this study establishes a generalized framework that systematically relates elevated Tg values of CAMs to intermolecular interactions based on specific functional groups. CAMs were prepared via quench-cooling using various combinations of indomethacin, ketoprofen, flurbiprofen, flufenamic acid, aripiprazole, bifonazole, and clotrimazole. CAMs prepared with drugs containing the COOH group exhibited significant positive deviations from the Tg values predicted by the Gordon-Taylor equation (i.e., ideal mixing behavior). COOH-associated hydrogen bonding was determined to be a key factor for Tg elevation, with synergistic contributions from π-π interactions and halogen bonding. In CAMs exhibiting the largest Tg deviations, contributions from ionic bonding were crucial, and were likely favored by differences in the pKa values of the constituent drugs. Continuity in Tg as a function of varying molar ratios indicated that stoichiometric pairing had a relatively minor contribution, while a decrease in the width of the glass transition suggested enhancement of molecular cooperativity as a possible mechanism for CAM stabilization. In contrast, non-COOH hydrogen bonding, π-π interactions, and halogen bonding on their own did not result in any meaningful Tg deviations from theoretical predictions. Systematic correlations between Tg deviations and molecular interactions reported in this study can lead to generalized design rules for the development of stable CAMs.

Molar Ratio-Dependent Crystallization in Coamorphous Celecoxib-Carbamazepine Systems: The Interplay of Thermodynamics and Kinetics

Coamorphous drug delivery systems have emerged as a promising formulation strategy to enhance the solubility, oral bioavailability, and physical stability of poorly water-soluble drugs. The molar ratio of components in coamorphous systems plays a critical role in determining their physical stability. In this study, we investigated the crystallization behavior of coamorphous celecoxib-carbamazepine (CEL-CBZ) systems at different molar ratios. The growth rates of CEL crystals, CBZ crystals, and CEL-CBZ cocrystals were observed to exhibit distinct dependencies on the molar ratio of coamorphous systems, primarily due to their unique thermodynamic driving forces, despite sharing the same kinetic factor. The influence of the molar ratio on the crystallization of coamorphous systems arises from the interplay between its effects on molecular mobility and thermodynamic driving forces, leading to either cooperative or competing effects. Both the crystal growth and crystallization tendency results reveal that thermodynamics plays a more dominant role than kinetics in the crystallization of coamorphous CEL-CBZ systems across various molar ratios. This study provides fundamental insights into the mechanism by which the molar ratio influences the crystallization of coamorphous systems, highlighting the complex crystallization behavior of multicomponent amorphous systems as an interplay between kinetics and thermodynamics.

Investigation of a Palbociclib and Naringin Co-Amorphous System to Ameliorate Anticancer Potential: Insights on In Silico Modeling, Physicochemical Characterization, Ex Vivo Permeation, and In Vitro Efficacy

Palbociclib (PCB), categorized as a BCS class II drug, is characterized by low aqueous solubility. The drug's limited aqueous solubility and poor dissolution rate pose significant challenges, potentially affecting its absorption and overall therapeutic efficacy. Co-amorphous (CAM) systems have been extensively investigated as a potential solution to overcome the issue of poor water solubility in numerous active pharmaceutical ingredients. This research study hypothesized that the coamorphization process involving the compounds PCB and naringin (NG) would lead to an increase in the aqueous solubility of PCB. Additionally, it was proposed that this process would also enhance the anticancer impact of PCB since NG is recognized for its pharmacological impact on breast cancer cells. In silico studies, it was revealed that PCB could interact with NG via hydrogen bonding. Furthermore, the prepared CAM (PCB-NG-CAM) system using PCB and NG was characterized by PXRD, DSC, FTIR, Raman spectroscopy, solid-state 13C nuclear magnetic resonance, and SEM. PCB-NG-CAM exhibited a significant increase in solubility, dissolution rate, and intestinal permeation compared to crystalline PCB. Furthermore, PCB-NG-CAM exhibited excellent physical stability at 40 °C/75% RH for up to 3 months. In addition, PCB-NG-CAM showed superior in vitro efficacy on MDA-MB-231 triple-negative breast cancer cell lines. PCB-NG-CAM resulted in a 2.24 times higher apoptosis rate and a 1.6 times greater ROS production than free PCB. Additionally, the inhibitory effect on cell migration and alterations in MMP was more pronounced in cells treated with PCB-NG-CAM. Therefore, this study indicated that PCB-NG-CAM has the potential to significantly improve the oral administration, solubility, and therapeutic efficacy of PCB.

"Aging" in co-amorphous systems: Dissolution decrease and non-negligible dissolution increase during storage without recrystallization

Developing co-amorphous systems is a promising strategy to improve the water solubility of poorly water-soluble drugs. Most of the studies focused on the initial dissolution rate of the fresh co-amorphous systems, and only physical stability was investigated after storage. However, the maintenance of the enhanced dissolution rate of co-amorphous systems after storage is necessary for further product development. The maintenance of amorphous forms after storage does not always mean the maintenance of the dissolution rate. In this study, indomethacin, arginine, tryptophan, and phenylalanine were used as the model drug and the co-formers to prepare co-amorphous systems and then stored under dry condition and RH 60 ± 5 % condition. No recrystallization was observed after the storage for 40 d and 80 d. Interestingly, both intrinsic dissolution rate (IDR) decrease and unexpected increase after storage were confirmed. The further mixing of IND and the co-former at a molecular level and the moisture changes of the co-amorphous systems during storage were supposed to play important roles in the aging. This study reminds us that the possible dissolution changes (both dissolution decrease and increase) of co-amorphous systems during storage should be carefully considered, though these samples maintained amorphous forms.

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.

Near UV and Visible Light Photodegradation in Solid Formulations: Generation of Carbon Dioxide Radical Anions from Citrate Buffer and Fe(III)

Near UV and visible light photodegradation can target therapeutic proteins during manufacturing and storage. While the underlying photodegradation pathways are frequently not well-understood, one important aspect of consideration is the formulation, specifically the formulation buffer. Citrate is a common buffer for biopharmaceutical formulations, which can complex with transition metals, such as Fe(III). In an aqueous solution, the exposure of such complexes to light leads to the formation of the carbon dioxide radical anion (•CO2-), a powerful reductant. However, few studies have characterized such processes in solid formulations. Here, we show that solid citrate formulations containing Fe(III) lead to the photochemical formation of •CO2-, identified through DMPO spin trapping and HPLC-MS/MS analysis. Factors such as buffers, the availability of oxygen, excipients, and manufacturing processes of solid formulations were evaluated for their effect on the formation of •CO2- and other radicals such as •OH.

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.

Destabilization of Indomethacin-Paracetamol Co-Amorphous Systems by Mechanical Stress

Using co-amorphous systems (CAMS) has shown promise in addressing the challenges associated with poorly water-soluble drugs. Quench-cooling is a commonly used CAMS preparation method, often followed by grinding or milling to achieve a fine powder that is suitable for subsequent characterization or further down-stream manufacturing. However, the impact of mechanical stress applied to CAMS has received little attention. In this study, the influence of mechanical stress on indomethacin-paracetamol CAMS was investigated. The investigation involved thermal analysis and solid-state characterization across various CAMS mixing ratios and levels of mechanical stress. The study revealed a negative effect of mechanical stress on stability, particularly on the excess components in CAMS. Higher levels of mechanical stress were observed to induce phase separation or recrystallization. Notably, samples at the optimal mixing ratio demonstrated greater resistance to the destabilization caused by mechanical stress. These results showed the significance of careful consideration of processing methods during formulation and the significance of optimizing mixing ratios in CAMS.

Amorphization of different furosemide polymorphic forms during ball milling: Tracking solid-to-solid phase transformations

Ball milling is used, not only to reduce the particle size of pharmaceutical powders, but also to induce changes in the physical properties of drugs. In this work we prepared three crystal forms of furosemide (forms Ⅰ, Ⅱ, and Ⅲ) and studied their solid phase transformations during ball milling. Powder X-ray diffraction and modulated differential scanning calorimetry were used to characterize the samples after each milling time on their path to amorphization. Our results show that forms Ⅰ and III directly converted into an amorphous phase, while form Ⅱ first undergoes a polymorphic transition to form Ⅰ, and then gradually loses its crystallinity, finally reaching full amorphousness. During ball milling of forms Ⅰ and Ⅱ, the glass transition temperature (Tg) of the amorphous fraction of the milled material remains almost unchanged at 75 °C and 74 °C, respectively (whilst the amorphous content increases). In contrast, the Tg values of the amorphous fraction of milled form III increase with increasing milling times, from 63 °C to 71 °C, indicating an unexpected phenomenon of amorphous-to-amorphous transformation. The amorphous fraction of milled forms I and II samples presented a longer structural relaxation (i.e., lower molecular mobility) than the amorphous fraction of milled form III samples. Moreover, the structural relaxation time remained the same for the increasing amorphous fraction during milling of forms I and II. In contrast, the structural relaxation times were always shorter for the amorphous fraction of form III, but increased with increasing amorphous content during milling, confirming amorphous-to-amorphous transformation.

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.

Genistein Co-Amorphous Systems with Amino Acids: An Investigation into Enhanced Solubility and Biological Activity

Genistein, an isoflavone known for its antioxidant and antidiabetic effects, suffers from the drawback of low solubility. To overcome this limitation, co-amorphous systems were synthesized by incorporating amino acids that were chosen through computational methods. The confirmation of the amorphous state of lysine and arginine-containing systems was ascertained by X-ray powder diffraction. Subsequently, the characterization of these systems was extended by employing thermo-gravimetry, differential scanning calorimetry, Fourier-transform infrared spectroscopy, and scanning electron microscopy. The investigation also included an assessment of the physical stability of the samples during storage. The apparent solubility of the systems was studied in an aqueous medium. To evaluate the in vitro permeability through the gastrointestinal tract, the parallel artificial membrane permeability assay was employed. The biological properties of the systems were assessed with regard to their antioxidant activity using 2,2-diphenyl-1-picrylhydrazyl and cupric ion-reducing antioxidant capacity assays, as well as their ability to inhibit α-glucosidase. The systems' glass transition temperatures were determined, and their homogeneity confirmed via differential scanning calorimetry analysis, while Fourier-transform infrared spectroscopy analysis provided data on molecular interactions. Stability was maintained for the entire 6-month storage duration. The co-amorphous system containing lysine displayed the most pronounced apparent solubility improvement, as well as a significant enhancement in antioxidant activity. Notably, both systems demonstrated superior α-glucosidase inhibition relative to acarbose, a standard drug for managing type 2 diabetes. The results indicate that co-amorphous systems with lysine and arginine have the potential to significantly enhance the solubility and biological activity of genistein.

Solubility and Physical Stability Enhancement of Loratadine by Preparation of Co-Amorphous Solid Dispersion with Chlorpheniramine and Polyvinylpyrrolidone

Loratadine (LRD), a non-sedating and slow-acting antihistamine, is often given in combination with short-onset chlorpheniramine maleate (CPM) to increase efficacy. However, LRD has poor water solubility resulting in low bioavailability. The aim of this study was to improve LRD solubility by preparing co-amorphous LRD-CPM. However, the obtained co-amorphous LRD-CPM recrystallized rapidly, and the solubility of LRD returned to a poor state again. Therefore, co-amorphous LRD-CPM solid dispersions using polyvinylpyrrolidone (PVP) as a carrier were prepared. The obtained solid dispersions were characterized using X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FT-IR). The solubility, dissolution, and mechanism of drug release from the LRD-CPM/PVP co-amorphous solid dispersions were studied and compared with those of intact LRD, LRD/PVP solid dispersions, and co-amorphous LRD-CPM mixtures. The results from XRPD and DSC confirmed the amorphous form of LRD in the co-amorphous solid dispersions. The FTIR results indicated that there was no intermolecular interaction between LRD, CPM, and PVP. In conclusion, the obtained LRD-CPM/PVP co-amorphous solid dispersions can successfully increase the water solubility and dissolution of LRD and extend the amorphous state of LRD without recrystallization.

Water dynamics on the structural properties of some NSAID's with leucine in the picosecond region using time domain spectroscopy

Concentration-dependent dielectric response for non-steroidal anti-inflammatory drugs (NSAIDs): Aceclofenac (ACF) and Diclofenac (DCF) in the aqueous leucine solution have been reported at different concentrations and temperatures (298.15 K to 283.15 K). The time domain reflectometry technique in the frequency region of 1 GHz to 30 GHz was used for the present study. Complex permittivity (ε*), static dielectric constant (ε), dielectric relaxation time (τ), dipole moment (μ) and Kirkwood correlation factor (g) have been calculated and discussed in terms of the molecular interaction of water and the used drugs. To give more insights into the structural dynamics of drug-induced amino acids, the study includes molar enthalpy of activation (ΔH), entropy of activation (ΔS), and free energy of activation (ΔF). The overall study concludes that the drug (DCF) having a potent inhibitor of cyclooxygenase found a higher static dielectric constant (ε0) than that of the drug (ACF) having more carbon (C), hydrogen (H), and oxygen (O) in the chain, which is more efficient in controlling pain.Communicated by Ramaswamy H. Sarma.

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.

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.

Coamorphous Systems of Valsartan: Thermal Analysis Contribution to Evaluate Intermolecular Interactions Effects on the Structural Relaxation

Coamorphous formation in binary systems of valsartan (Val) with 4,4'-bipyridine (Bipy) and trimethoprim (Tri) was investigated for mixtures with a mole fraction of 0.16~0.86 of valsartan and evaluated in terms of the glass transition temperature. The glass transition of the systems had a behavior outside the values predicted by the Gordon-Taylor equation, showing that Val-Bipy (hydrogen bonding between the components) had a lower deviation and Val-Tri (ionic bonding between the components) had a higher deviation. Mixtures of compositions 2:1 Val-Bipy and 1:1 Val-Tri were selected for further investigation and verified to be stable, as no crystallization was observed during subsequent heating and cooling programs. For these systems, the effective activation energy during glass transition was evaluated. Compared to pure valsartan, the system with the lower glass transition temperature (Val-Bipy) presented the highest effective activation energy, and the system with the higher glass transition temperature (Val-Tri) presented a lower effective activation energy. The results presented a good correlation between the data obtained from two different techniques to determine the fragility and effective activation energy: non-isothermal kinetic analysis by DSC and TSDC.

Design and evaluation of oral formulation for apixaban

Non-valvular atrial fibrillation (NVAF) is a common form of cardiac arrhythmia that affects 1-1.5% of adults and roughly 10% of elderly adults with dysphagia. Apixaban is an anticoagulant referred to as a factor Xa inhibitor, which has been shown to reduce the risk of stroke and systemic embolism in cases of NVAF. Our objective in the current study was to formulate an orally disintegrating film to facilitate the administration of apixaban to elderly patients who have difficulty swallowing. Researchers have used a wide variety of cellulose-based or non-cellulose-based polymers in a variety of combinations to achieve specific characteristics related to film formation, disintegration performance, drug content, in vitro drug release, and stability. One of the two formulations in this study was specify that bioequivalence criteria met with respect to Cmax of the reference drug (ELIQUIS®) in terms of pharmacokinetic profile. Further research will be required to assess the applicability of orodispersible films created using colloidal polymers of high and low molecular weights to other drugs with poor solubility in water.

Preparation of Co-Amorphous Levofloxacin Systems for Pulmonary Application

Addressing antimicrobial resistance requires new approaches in various disciplines of pharmaceutical sciences. The fluoroquinolone levofloxacin (LEV) plays an important role in the therapy of lung infections. However, its effectiveness is limited by its severe side effects involving tendinopathy, muscle weakness and psychiatric disturbance. Therefore, there is a need for the development of an effective formulation of LEV with reduced systemic drug concentrations, thereby also reducing the consumption and excretion of antibiotics or metabolites. This study aimed for the development of a pulmonary-applicable LEV formulation. Co-amorphous LEV-L-arginine (ARG) particles were prepared by spray drying and characterised by scanning electron microscopy, modulated differential scanning calorimetry, X-ray powder diffraction, Fourier-transform infrared spectroscopy and next generation impactor analysis. Co-amorphous LEV-ARG salts were produced independently of varying process parameters. The use of 30% (v/v) ethanol as a solvent led to better aerodynamic properties compared to an aqueous solution. With a mass median aerodynamic diameter of just over 2 µm, a fine particle fraction of over 50% and an emitted dose of over 95%, the product was deemed suitable for a pulmonary application. The created process was robust towards the influence of temperature and feed rate, as changing these parameters did not have a significant influence on the critical quality attributes, indicating the feasibility of producing pulmonary-applicable co-amorphous particles for sustainable antibiotic therapy.

Co-amorphous systems consisting of indomethacin and the chiral co-former tryptophan: Solid-state properties and molecular mobilities

In this study the influence of an enantiomeric co-former and the preparation method on the solid-state properties and physical stability of co-amorphous systems were investigated. Co-amorphous systems consisting of indomethacin (IND) and chiral tryptophan (TRP) as co-former in its two enantiomeric forms, as racemate, and as conglomerate (equimolar mixture of D- and L-TRP) were prepared. Co-amorphization was achieved by ball milling (BM) and spray drying (SD). The effects of chirality and preparation method on the solid-state properties and physical stabilities of the systems were investigated by XRPD, FTIR and mDSC. Differences in the BM process were caused by the enantiomeric properties of the co-former: The IND/TRP conglomerate (IND/TRPc) turned co-amorphous after 60 min. In contrast, co-amorphization of IND/L-TRP and IND/D-TRP required 80 min of ball milling, respectively, and the co-amorphous IND/TRP racemate (IND/TRPr) was obtained only after 90 min of ball milling. Although the intermolecular interactions of the co-amorphous systems prepared by BM and SD were similar (determined by FTIR), the T_g values differed (∼87 °C for the ball milled and ∼62 °C for the spray dried systems). The physical stabilities of the ball milled co-amorphous systems varied between 3 and 11 months if stored at elevated temperature and dry conditions, with the highest stability for the IND/TRPc system and the lowest stability for the IND/TRPr system, and these differences correlated with the calculated relaxation times. In contrast, all spray dried systems were stable only for 1 month and their relaxation times were similar. It could be shown that the chirality of a co-former and the preparation method influence the solid-state properties, thermal properties and physical stability of IND/TRP systems.

Solid–Liquid Equilibrium in Co-Amorphous Systems: Experiment and Prediction

In this work, the solid–liquid equilibrium (SLE) of four binary systems combining two active pharmaceutical ingredients (APIs) capable of forming co-amorphous systems (CAMs) was investigated. The binary systems studied were naproxen-indomethacin, naproxen-ibuprofen, naproxen-probucol, and indomethacin-paracetamol. The SLE was experimentally determined by differential scanning calorimetry. The thermograms obtained revealed that all binary mixtures investigated form eutectic systems. Melting of the initial binary crystalline mixtures and subsequent quenching lead to the formation of CAM for all binary systems and most of the compositions studied. The experimentally obtained liquidus and eutectic temperatures were compared to theoretical predictions using the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state and conductor-like screening model for real solvents (COSMO-RS), as implemented in the Amsterdam Modeling Suite (COSMO-RS-AMS). On the basis of the obtained results, the ability of these models to predict the phase diagrams for the investigated API–API binary systems was evaluated. Furthermore, the glass transition temperature (Tg) of naproxen (NAP), a compound with a high tendency to recrystallize, whose literature values are considerably scattered, was newly determined by measuring and modeling the Tg values of binary mixtures in which amorphous NAP was stabilized. Based on this analysis, erroneous literature values were identified.

Influence of Co-amorphization on the Physical Stability and Dissolution Performance of an Anthelmintic Drug Flubendazole

In this work, the co-amorphization approach was applied to flubendazole (FluBZ), resulting in the formation of two novel solid forms of FluBZ with l-phenylalanine (Phe) and l-tryptophan (Trp). A variety of physicochemical techniques have been used to describe new systems, including powder X-ray diffraction, thermal methods, infrared spectroscopy, and scanning electron microscopy. Co-amorphization has been shown to suppress crystallization tendency and considerably increase the shelf-life storage of amorphous flubendazole solid across a wide range of relative humidities. The dissolution behavior of the amorphous forms in biorelevant media at pH = 1.6, pH = 6.5, and 37 °C has been studied in terms of C_max (maximum FluBZ concentration), T_max (time to attain peak drug concentration), and AUC (concentration area under the curve during dissolution). At pH = 6.5, a continuous supersaturation and the highest AUC value of all examined systems were observed for the FluBZ-Phe (1:1) system. The phase solubility diagrams revealed that the reason for the better dissolution performance of FluBZ-Phe (1:1) at pH = 6.5 is a complexation between the components in a solution. This work highlights the applicability of co-amorphous systems in improving the physical stability and dissolution performance of drug compounds with poor biopharmaceutical characteristics.

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.

Selecting Counterions to Improve Ionized Hydrophilic Drug Encapsulation in Polymeric Nanoparticles

Hydrophobic ion pairing (HIP) can successfully increase the drug loading and control the release kinetics of ionizable hydrophilic drugs, addressing challenges that prevent these molecules from reaching the clinic. Nevertheless, polymeric nanoparticle (PNP) formulation development requires trial-and-error experimentation to meet the target product profile, which is laborious and costly. Herein, we design a preformulation framework (solid-state screening, computational approach, and solubility in PNP-forming emulsion) to understand counterion-drug-polymer interactions and accelerate the PNP formulation development for HIP systems. The HIP interactions between a small hydrophilic molecule, AZD2811, and counterions with different molecular structures were investigated. Cyclic counterions formed amorphous ion pairs with AZD2811; the 0.7 pamoic acid/1.0 AZD2811 complex had the highest glass transition temperature (Tg; 162 °C) and the greatest drug loading (22%) and remained as phase-separated amorphous nanosized domains inside the polymer matrix. Palmitic acid (linear counterion) showed negligible interactions with AZD2811 (crystalline-free drug/counterion forms), leading to a significantly lower drug loading despite having similar log P and pKa with pamoic acid. Computational calculations illustrated that cyclic counterions interact more strongly with AZD2811 than linear counterions through dispersive interactions (offset π-π interactions). Solubility data indicated that the pamoic acid/AZD2811 complex has a lower organic phase solubility than AZD2811-free base; hence, it may be expected to precipitate more rapidly in the nanodroplets, thus increasing drug loading. Our work provides a generalizable preformulation framework, complementing traditional performance-indicating parameters, to identify optimal counterions rapidly and accelerate the development of hydrophilic drug PNP formulations while achieving high drug loading without laborious trial-and-error experimentation.

Solventless amorphization and pelletization using a high shear granulator. Part II; Preparation of co-amorphous mixture-layered pellets using indomethacin and arginine

The aim of this study was to investigate the preparation of co-amorphous mixture-layered pellets using solventless pelletization and amorphization using a high shear granulator (as suggested in the first part of this study) by high shear mixing of drug crystals and a crystalline co-former with inactive spheres. Mixtures of crystalline indomethacin and arginine at various molar ratios were mixed with microcrystalline cellulose spheres at a weight ratio of 1:10 using the granulator and the resulting particles were characterized using solid-state and particle analytical techniques as well as dissolution testing and physical stability. At jacket temperatures of 20 °C or more of the granulator, co-processing of indomethacin and arginine enhanced amorphization of indomethacin and provided a co-amorphous mixture due to homogenous mixing of indomethacin and arginine amorphous phases. The co-amorphous mixture was deposited on the surface of the spheres, yielding co-amorphous mixture-layered pellets. The co-amorphous mixtures at molar ratios of indomethacin to arginine of 2:1 and 1:1, deposited on the pellets, did not recrystallize for at least 4 weeks. The pellets exhibited higher dissolution characteristics as additional hypromellose could prevent precipitation. These findings demonstrate the potential of this technique as a solventless approach to prepare co-amorphous mixture-layered pellets through a one-step process.

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.

Influence of Water on Amorphous Lidocaine

Water is generally regarded as a universal plasticizer of amorphous drugs or amorphous drug-containing systems. A decrease in glass-transition temperature (T_g) is considered the general result of this plasticizing effect. A recent study exhibits that water can increase the T_g of amorphous prilocaine (PRL) and thus shows an anti-plasticizing effect. The structurally similar drug lidocaine (LID) might show similar interactions with water, and thus an anti-plasticizing effect of water is hypothesized to also occur in amorphous LID. However, the influence of water on the T_g of LID cannot be determined directly due to the very low stability of LID in the amorphous form. It is possible to predict the T_g of LID from a co-amorphous system of PRL-LID using the Gordon-Taylor equation. Interactions were observed between PRL and LID based on the deviations between the experimental T_gs and the T_gs calculated by the conventional use of the Gordon-Taylor equation. A modified use of the Gordon-Taylor equation was applied using the optimal co-amorphous system as a separate component and the excess drug as the other component. The predicted T_g of fully hydrated LID could thus be determined and was found to be increased by 0.9 ± 0.7 K compared with the T_g of water-free amorphous LID. It could be shown that water exhibited a small anti-plasticizing effect on LID.

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.

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.

Optimization of Methionine in Inhalable High-dose Spray-dried Amorphous Composite Particles using Response Surface Method, Infrared and Low frequency Raman Spectroscopy

The influence of amino acids, other than leucine, in improving aerosolization of inhalable powders has not been widely explored. This detailed study focused on the use of methionine, another promising endogenous amino acid, in high dose spray-dried co-amorphous powders by investigating the influence of methionine proportion (0 - 20% ^w/_w), and feed concentration (0.2 - 0.8% ^w/_v) on aerosolization of kanamycin, a model drug, using a design of experiment approach. Low frequency Raman spectroscopy was used to assess the stability of the powders stored at 25 °C/53% relative humidity over 28 days. An increase in concentration of methionine was associated with an increase in fine particle fraction (FPF), with the highest FPF of 84% being achieved at 20% ^w/_w and 0.2% ^w/_v feed concentration. With an increase in feed concentration, both yield and particle size increased for all formulations; the FPF did not change except for kanamycin only formulation in which it decreased. During storage at high humidity, similar aerosolization stabilities were offered by different proportions of methionine although methionine crystallized out in all formulations. Furthermore, the crystallization was accompanied by surface enrichment of methionine on the particles. This study suggests that there is a direct relationship between methionine content and aerosolization for kanamycin-methionine amorphous matrices but feed concentration has little effect. In addition, methionine proportion has no effect on physical stability of such matrices at high humidity.

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℃.

Amino acids and its pharmaceutical applications: A mini review

Amino acids are natural compounds that can be safely used in pharmaceutical applications. Considering the great interest in the amino acids used in the pharmaceutical industry, this article presents an overview of investigations reported in recent years. In this regard, the first sections begin with an introductory description of the properties, classification and safety of amino acids, while in the other sections the most common methods for the preparation of amino acids formulations and their application on solubilization, permeation and stabilization of several active pharmaceutical ingredients are described. Furthermore, available data about the multicomponent systems approach is included. Lastly, the impact of amino acids formulations on therapeutic efficacy is explored. The advantages illustrated suggest that amino acids are capable of improving the biopharmaceutical properties of drugs.

Prediction of the Synergistic Glass Transition Temperature of Coamorphous Molecular Glasses Using Activity Coefficient Models

The glass transition temperature (T_g) of a binary miscible mixture of molecular glasses, termed a coamorphous glass, is often synergistically increased over that expected for an athermal mixture due to the strong interactions between the two components. This synergistic interaction is particularly important for the formulation of coamorphous pharmaceuticals since the molecular interactions and resulting T_g strongly impact stability against crystallization, dissolution kinetics, and bioavailability. Current models that describe the composition dependence of T_g for binary systems, including the Gordon-Taylor, Fox, Kwei, and Braun-Kovacs equations, fail to describe the behavior of coamorphous pharmaceuticals using parameters consistent with experimental ΔC_P and Δα. Here, we develop a robust thermodynamic approach extending the Couchman and Karasz method through the use of activity coefficient models, including the two-parameter Margules, non-random-two-liquid (NRTL), and three-suffix Redlich-Kister models. We find that the models, using experimental values of ΔC_P and fitting parameters related to the binary interactions, successfully describe observed synergistic elevations and inflections in the T_g versus composition response of coamorphous pharmaceuticals. Moreover, the predictions from the NRTL model are improved when the association-NRTL version of that model is used. Results are reported and discussed for four different coamorphous systems: indomethacin-glibenclamide, indomethacin-arginine, acetaminophen-indomethacin, and fenretinide-cholic acid.

Hot-Melt Extrusion: a Roadmap for Product Development

Hot-melt extrusion has found extensive application as a feasible pharmaceutical technological option over recent years. HME applications include solubility enhancement, taste masking, and sustained drug release. As bioavailability enhancement is a hot topic of today's science, one of the main applications of HME is centered on amorphous solid dispersions. This review describes the most significant aspects of HME technology and its use to prepare solid dispersions as a drug formulation strategy to enhance the solubility of poorly soluble drugs. It also addresses molecular and thermodynamic features critical for the physicochemical properties of these systems, mainly in what concerns miscibility and physical stability. Moreover, the importance of applying the Quality by Design philosophy in drug development is also discussed, as well as process analytical technologies in pharmaceutical HME monitoring, under the current standards of product development and regulatory guidance. Graphical Abstract.

The influence of moisture on the storage stability of co-amorphous systems

Co-amorphization has been utilized to improve the physical stability of the respective neat amorphous drugs. However, physical stability of co-amorphous systems is mostly investigated under dry conditions, leaving the potential influence of moisture on storage stability unclear. In this study, carvedilol-L-aspartic acid (CAR-ASP) co-amorphous systems at CAR to ASP molar ratios from 3:1 to 1:3 were investigated under non-dry conditions at two temperatures, i.e., 25 °C 55 %RH and 40 °C 55 %RH. Under these conditions, the highest physical stability of CAR-ASP systems was observed at the 1:1 M ratio. This finding differed from the optimal molar ratio previously obtained under dry conditions (CAR-ASP 1:1.5). Molecular interactions between CAR and ASP were affected by moisture, and salt disproportionation occurred during storage. Morphological differences of systems at different molar ratios could be observed already after one week of storage. Furthermore, variable temperature X-ray powder diffraction measurements showed that excess CAR or excess ASP, existing in the binary systems, resulted in a faster recrystallization compared to equimolar system. Overall, this study emphasizes the influence of moisture on co-amorphous systems during storage, and provides options to determine the optimal ratio of co-amorphous systems in presence of moisture at comparatively short storage times.

Considerations for the selection of co-formers in the preparation of co-amorphous formulations

Co-amorphous drug delivery systems are evolving as a credible alternative to amorphous solid dispersions technology. In Co-amorphous systems (CAMs), a drug is stabilized in amorphous form using small molecular weight compounds called as co-formers. A wide variety of small molecular weight co-formers have been leveraged in the preparation of CAMs. The stability and supersaturation potential of prepared co-amorphous phases largely depend on the type of co-former employed in the CAMs. However, the rationality behind the co-former selection in co-amorphous systems is poorly understood and scarcely compiled in the literature. There are various facets to the rational selection of co-former for CAMs. In this context, the present review compiles various factors affecting the co-former selection. The factors have been broadly classified under Thermodynamic, Kinetic and Pharmacokinetic-Pharmacologically relevant parameters. In particular, the importance of Glass transition, Miscibility, Liquid-Liquid phase separation (LLPS), Crystallization inhibition has been deliberated in detail.

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.

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.

Co-Amorphous Formulations of Furosemide with Arginine and P-Glycoprotein Inhibitor Drugs

In this study, the amino acid arginine (ARG) and P-glycoprotein (P-gp) inhibitors verapamil hydrochloride (VER), piperine (PIP) and quercetin (QRT) were used as co-formers for co-amorphous mixtures of a Biopharmaceutics classification system (BCS) class IV drug, furosemide (FUR). FUR mixtures with VER, PIP and QRT were prepared by solvent evaporation, and mixtures with ARG were prepared by spray drying in 1:1 and 1:2 molar ratios. The solid-state properties of the mixtures were characterized with X-ray powder diffraction (XRPD), Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) in stability studies under different storage conditions. Simultaneous dissolution/permeation studies were conducted in side-by-side diffusion cells with a PAMPA (parallel artificial membrane permeability assay) membrane as a permeation barrier. It was observed with XRPD that ARG, VER and PIP formed co-amorphous mixtures with FUR at both molar ratios. DSC and FTIR revealed single glass transition values for the mixtures (except for FUR:VER 1:2), with the formation of intermolecular interactions between the components, especially salt formation between FUR and ARG. The co-amorphous mixtures were found to be stable for at least two months under an elevated temperature/humidity, except FUR:ARG 1:2, which was sensitive to humidity. The dissolution/permeation studies showed that only the co-amorphous FUR:ARG mixtures were able to enhance both the dissolution and permeation of FUR. Thus, it is concluded that formulating co-amorphous salts with ARG may be a promising option for poorly soluble/permeable FUR.

Impact of the Chain Length and Topology of the Acetylated Oligosaccharide on the Crystallization Tendency of Naproxen from Amorphous Binary Mixtures

The impact of the chain length or dispersity of polymers in controlling the crystallization of amorphous active pharmaceutical ingredients (APIs) has been discussed for a long time. However, because of the weak control of these parameters in the majority of macromolecules used in pharmaceutical formulations, the abovementioned topic is poorly understood. Herein, four acetylated oligosaccharides, maltose (acMAL), raffinose (acRAF), stachyose (acSTA), and α-cyclodextrin (ac-α-CD) of growing chain lengths and different topologies (linear vs cyclic), mimicking the growing backbone of the polymer, were selected to probe the influence of these structural factors on the crystallization of naproxen (NAP)—an API that does not vitrify regardless of the cooling rate applied in our experiment. It was found that in equimolar systems composed of NAP and linear acetylated oligosaccharides, the progress and activation barrier for crystallization are dependent on the molecular weight of the excipient despite the fact that results of Fourier transform infrared studies indicated that there is no difference in the interaction pattern between measured samples. On the other hand, complementary dielectric, calorimetric, and X-ray diffraction data clearly demonstrated that NAP mixed with ac-α-CD (cyclic saccharide) does not tend to crystallize even in the system with a much higher content of APIs. To explain this interesting finding, we have carried out further density functional theory computations, which revealed that incorporation of NAP into the cavity of ac-α-CD is hardly possible because this state is of much higher energy (up to 80 kJ/mol) with respect to the one where the API is located outside of the saccharide torus. Hence, although at the moment, it is very difficult to explain the much stronger impact of the cyclic saccharide on the suppression of crystallization and enhanced stability of NAP with respect to the linear carbohydrates, our studies clearly showed that the chain length and the topology of the excipient play a significant role in controlling the crystallization of this API.

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.

Predictive identification of co-formers in co-amorphous systems

This work aims to understand the properties of co-formers that form co-amorphous pharmaceutical materials and to predict co-amorphous system formation. A partial least square - discriminant analysis (PLS-DA) was performed using known co-amorphous systems described by 36 variables based on the properties of the co-former and the binding energy of the system. The PLS-DA investigated the propensity to form co-amorphous material of the active pharmaceutical ingredients: mebendazole, carvedilol, indomethacin, simvastatin, carbamazepine and furosemide in combination with 20 amino acid co-formers. The variables that were found to favour the propensity to form co-amorphous systems appear to be a relatively large value for average molecular weight and the sum of the difference between hydrogen bond donors and hydrogen bond acceptors for both components, and a relatively small or negative value for excess enthalpy of mixing, excess enthalpy of hydrogen bonding and the difference in the Hansen parameter for hydrogen bonding of the coformer and the active pharmaceutical ingredient (API). To test the predictive power of this model, 29 potential co-formers were used to form either co-amorphous or crystalline two-component materials with mebendazole. Of these 29 two-component systems, the co-amorphous nature of a total of 26 materials was correctly predicted by the model, giving a predictive hit rate of 90 %.

Characterization and therapeutic efficacy evaluation of glimepiride and L-arginine co-amorphous formulation prepared by supercritical antisolvent process: Influence of molar ratio and preparation methods

The glimepiride/L-arginine (GA) binary systems were prepared at various molar ratios by using a supercritical antisolvent (SAS) process. For comparison, the GA system was also prepared by physical mixing (PM), melt quenching (MQ), and solvent evaporation (SE) methods. Analyses by DSC and PXRD showed that only the GA binary mixture at 1:1 M ratio prepared by the SAS process was a pure co-amorphous mixture with an excellent content uniformity. On the other hand, GA mixture prepared by PM and SE were not pure co-amorphous systems and contained crystalline eutectic mixture, and MQ method at 170 °C induced the decrease in drug content due to decomposition of glimepiride. The positive deviation of experimentally measured glass transition temperature (T_g) compared to predicted T_g by the Gordon Taylor equation suggests specific molecular interactions between glimepiride and L-arginine in solid-state GA co-amorphous (GACA) mixture. The intermolecular interactions between glimepiride and L-arginine in GACA system were characterized by FT-IR and solid-state NMR analyses. Improved glimepiride dissolution rate of GACA formulation were confirmed using the solubility test, contact angle measurement, and dissolution test. Furthermore, the evaluation of pharmacodynamic hypoglycemic effect demonstrated that GACA prepared by the SAS process significantly improved the therapeutic efficacy of glimepiride.

Determination of the Optimal Molar Ratio in Amino Acid-Based Coamorphous Systems

Coamorphous drug formulations are a promising approach to improve solubility and bioavailability of poorly water-soluble drugs. On the basis of theoretical assumptions involving molecular interactions, the 1:1 molar ratio of drug and coformer is frequently used as "the optimal ratio" for a homogeneous coamorphous system (i.e., the coamorphous system with the highest physical stability and, if strong interaction is possible between two molecules, the highest glass transition temperature (T_g)). In order to more closely investigate this assumption, l-aspartic acid (ASP) and l-glutamic acid (GLU) were investigated as coformers for the basic drug carvedilol (CAR) at varying molar ratios. Salt formation between CAR with ASP or GLU was expected to occur at the molar 1:1 ratio based on their chemical structures. Interestingly, the largest deviation between the experimental T_g and the theoretical T_g based on the Gordon-Taylor equation was observed at a molar ratio of around 1:1.5 in CAR-ASP and CAR-GLU systems. In order to determine the exact value of the ratio with the highest T_g, a data fitting approach was established on thermometric data of various CAR-ASP and CAR-GLU systems. The highest T_g was found to be at CAR-ASP 1:1.46 and CAR-GLU 1:1.43 mathematically. Spectroscopic investigations and physical stability measurements further confirmed that the optimal molar ratio for obtaining a homogeneous system and the highest stability can be found at a molar ratio around 1:1.5. Overall, this study developed a novel approach to determine the optimal ratio between drug and coformers and revealed the influence of varying molar ratios on molecular interactions and physical stability in coamorphous systems.

Investigation of Potential Amorphisation and Co-Amorphisation Behaviour of the Benzene Di-Carboxylic Acids upon Cryo-Milling

Multi-component formulations offer a way to modulate the physico-chemical properties of drug molecules and thereby enhance their efficacy as medicines compared to using only the raw drug, with mechano-chemical synthesis being an increasingly popular way to create these novel materials in a research setting. However, to date studies have focussed on employing pharmaceutically acceptable components, which has led to the literature featuring chemically diverse pairings of drug and excipient. Here we investigate the outcome of cryo-milling and co-cryo-milling of a series of three simple geometrical isomers of benzene di-carboxylic acid with a view to developing a chemically simple model system to investigate areas including cryo-milling, co-cryo-milling, co-amorphous formulation, etc. All three single-component materials exhibit differing behaviour upon cryo-milling and subsequent storage, as do the two-component mixtures. The surprisingly differing behaviours of these chemically similar species upon cryo-milling and co-cryo-milling suggest that molecular chemistry may not be the dominant influence on the outcome of mechano-chemical syntheses, and that other properties should be explored to develop a predictive model for the outcomes of these types of reactions.

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.

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.