A theoretical and spectroscopic study of co-amorphous naproxen and indomethacin

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

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

Mechanochemically Induced Solid-State Transformations of Levofloxacin

Levofloxacin hemihydrate (LVXh) is a complex fluoroquinolone drug that exists in both hydrated and anhydrous/dehydrated forms. Due to the complexity of such a compound, the primary aim of this study was to investigate the amorphization capabilities and solid-state transformations of LVXh when exposed to mechanical treatment using ball milling. Spray drying was utilized as a comparative method for investigating the capabilities of complete LVX amorphous (LVXam) formation. The solid states of the samples produced were comprehensively characterized by powder X-ray diffraction, thermal analysis, infrared spectroscopy, Rietveld method, and dynamic vapor sorption. The kinetics of the process and the quantification of phases at different time points were conducted by Rietveld refinement. The impact of the different mills, milling conditions, and parameters on the composition of the resulting powders was examined. A kinetic investigation of samples produced using both mills disclosed that it was in fact possible to partially amorphize LVXh upon mechanical treatment. It was discovered that LVXh first transformed to the anhydrous/dehydrated form γ (LVXγ), as an intermediate phase, before converting to LVXam. The mechanism of LVXam formation by ball milling was successfully revealed, and a new method of forming LVXγ and LVXam by mechanical forces was developed. Spray drying from water depicted that complete amorphization of LVXh was possible. The amorphous form of LVX had a glass transition temperature of 80 °C. The comparison of methods highlighted that the formation of LVXam is thus both mechanism- and process-dependent. Dynamic vapor sorption studies of both LVXam samples showed comparable stability properties and crystallized to the most stable hemihydrate form upon analysis. In summary, this work contributed to the detailed understanding of solid-state transformations of essential fluoroquinolones while employing greener and more sustainable manufacturing methods.

Development and characterization of co-amorphous griseofulvin/L-leucin by modified solvent processing hot-melt extrusion

Co-amorphous systems (CAMS) were developed between griseofulvin (GRI) and L-leucine (LEU) at 2:1 wt ratio, by application of a novel solvent assisted hot-melt extrusion (HME) method that involved wet processing/drying of the feeds prior to extrusion. CAMS formation was confirmed by powder crystallography (pXRD) and thermal analysis (DSC). Intermolecular H-bonding between the carbonyl groups of GRI and the hydroxyl and amino groups of LEU were identified by vibrational spectroscopy (ATR-FTIR). The measured glass transition temperatures (Tg) of the extrudates from feeds processed with aqueous acetic acid (AcOH) were markedly lower than that of neat amorphous GRI and values predicted from Gordon-Taylor equation, indicating plasticizing action of AcOH. Drug concentrations during dissolution of CAMS under non-sink conditions (Sink Index 0.0115) were up to x82 higher at plateau compared to crystalline drug solubility. The degree of supersaturation lasted for at least 24 h. Plasticizer (Compritol®/Kolliphor® 75/25) added before extrusion did not impact significantly on CAMS formation but altered the dissolution profile from a spring-and-parachute profile to gradual rise to maximum. These findings reinforce the application of drug/amino acid-based CAMS in formulation, particularly for high-dose drugs, for which polymers are unsuited due to the required large proportions.

Preparation and Characterization of a Rifampicin Coamorphous Material with Tromethamine Coformer: An Experimental-Theoretical Study

Rifampicin (RIF) is an antibiotic used to treat tuberculosis and leprosy. Even though RIF is a market-available drug, it has a low aqueous solubility, hindering its bioavailability. Among the strategies for bioavailability improvement of poorly soluble drugs, coamorphous systems have been revealed as an alternative in the increase of the aqueous solubility of drug systems and at the same time also increasing the amorphous state stability and dissolution rate when compared with the neat drug. In this work, a new coamorphous form from RIF and tromethamine (TRIS) was synthesized by slow evaporation. Structural, electronic, and thermodynamic properties and solvation effects, as well as drug-coformer intermolecular interactions, were studied through density functional theory (DFT) calculations. Powder X-ray diffraction (PXRD) data allowed us to verify the formation of a new coamorphous. In addition, the DFT study indicates a possible intermolecular interaction by hydrogen bonds between the available amino and carbonyl groups of RIF and the hydroxyl and amino groups of TRIS. The theoretical spectra obtained are in good agreement with the experimental data, suggesting the main interactions occurring in the formation of the coamorphous system. PXRD was used to study the physical stability of the coamorphous system under accelerated ICH conditions (40 °C and 75% RH), indicating that the material remained in an amorphous state up to 180 days. The thermogravimetry result of this material showed a good thermal stability up to 153 °C, and differential scanning calorimetry showed that the glass temperature (Tg) was at 70.0 °C. Solubility studies demonstrated an increase in the solubility of RIF by 5.5-fold when compared with its crystalline counterpart. Therefore, this new material presents critical parameters that can be considered in the development of new coamorphous formulations.

Use of solid thermolytic salts to facilitate microwave-induced in situ amorphization

Moisture was frequently used as dielectric heating source in classical microwave-able systems to facilitate microwave-induced in situ amorphization, however such systems may face the potential of drug hydrolysis. In this study, solid thermolytic salts were proposed to function as moisture substitutes and their feasibility and impacts on microwave-induced in situ amorphization were investigated. It was found that NH4HCO3 was a promising solid alkaline salt to facilitate both microwave-induced in situ amorphization and in situ salt formation of acidic indomethacin (IND). Moreover, it could improve the chemical stability of the drug and the dissolution performance of compacts relative to classical moisture-based compacts upon microwaving. Further mechanistic study suggested that the in situ amorphization occurred prior to the in situ salt formation, especially in formulations with low drug loadings and high solid salt mass ratios. For compacts with low polymer ratios, in situ salt formation took place subsequently, where the previously amorphized IND within compacts could interact with the NH3 gas produced in situ by the decomposition of NH4HCO3 and form the ammonium IND salt. Microwaving time showed great impacts on the decomposition of NH4HCO3 and the in situ generation of water and NH3, which indirectly affected the amorphization and salt formation of IND. In comparison to the moisture-based systems, the NH4HCO3-based system showed a number of advantages, including the reduced potential of IND hydrolysis due to the absence of absorbed moisture, a wider category of applicable polymeric carriers other than hygroscopic polymers, and an increase in drug loading up to 50% (w/w).

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

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

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.

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

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

Sinapic Acid Co-Amorphous Systems with Amino Acids for Improved Solubility and Antioxidant Activity

The objective of this study was to obtain co-amorphous systems of poorly soluble sinapic acid using amino acids as co-formers. In order to assess the probability of the interaction of amino acids, namely, arginine, histidine, lysine, tryptophan, and proline, selected as co-formers in the amorphization of sinapic acid, in silico studies were carried out. Sinapic acid systems with amino acids in a molar ratio of 1:1 and 1:2 were obtained using ball milling, solvent evaporation, and freeze drying techniques. X-ray powder diffraction results confirmed the loss of crystallinity of sinapic acid and lysine, regardless of the amorphization technique used, while remaining co-formers produced mixed results. Fourier-transform infrared spectroscopy analyses revealed that the co-amorphous sinapic acid systems were stabilized through the creation of intermolecular interactions, particularly hydrogen bonds, and the potential formation of salt. Lysine was selected as the most appropriate co-former to obtain co-amorphous systems of sinapic acid, which inhibited the recrystallization of sinapic acid for a period of six weeks in 30 °C and 50 °C. Obtained co-amorphous systems demonstrated an enhancement in dissolution rate over pure sinapic acid. A solubility study revealed a 12.9-fold improvement in sinapic acid solubility after introducing it into the co-amorphous systems. Moreover, a 2.2-fold and 1.3-fold improvement in antioxidant activity of sinapic acid was observed with respect to the ability to neutralize the 2,2-diphenyl-1-picrylhydrazyl radical and to reduce copper ions, respectively.

Poly (amino acid)s as new co-formers in amorphous solid dispersion

The drug-amino acid co-amorphous systems and amorphous solid dispersions (ASDs) are promising methods to address the poor water solubility of poorly water-soluble drugs. However, some amino acids might not be perfect co-formers for co-amorphous systems, and the relatively low drug-loading of many ASDs is one of the main disadvantages of ASDs. Thus, poly-l-lysine and polyglutamic acid were selected as the co-formers, ball milled with basic mebendazole, neutral tadalafil and acidic valsartan at different weight ratios (from 3:1 to 1:3) to prepare poly (amino acid)-based ASDs, aiming to combine the advantages of co-amorphous systems (high drug-loading) and ASDs (relatively high T_g and high physical stability). All the mixtures were converted into amorphous after milling. The powder dissolution studies showed that drug-poly (amino acid) ASDs improved the dissolution rate of the drug in different ways and to different degrees. Moreover, the two poly (amino acid)s enhanced the physical stability of amorphous drugs. It is worthy to mention that the salt formation between the drug and the poly (amino acid) does not necessarily mean better performance compared to non-salt forming systems, and salt formation is also not a prerequisite for the formation of promising drug-poly (amino acid) ASDs.

Mechanistic Study on Transformation of Coamorphous Baicalein-Nicotinamide to Its Cocrystal Form

Recently, coamorphization and cocrystal technologies are of particular interest in the pharmaceutical industry due to their ability to improve the solubility/dissolution and bioavailability of poorly water-soluble drugs, while the coamorphous system often tends to convert into the stable crystalline form usually crystalline physical mixture of each component during formulation preparation or storage. In this paper, BCS II drug baicalein (BAI) along with nicotinamide (NIC) were prepared into a single homogeneous coamorphous system with a single transition temperature at 42.5 °C. Interestingly, instead of the physical mixture of crystalline BAI and NIC, coamorphous BAI-NIC would transform to its cocrystal form under stress of temperature and humidity. The transformation rate under isothermal condition was temperature-dependent, since the crystallinity of the cocrystal enhanced as the temperature increased. Further mechanic studies showed the activation energy for the transformation under non-isothermal condition was calculated to be 184.52 kJ/mol. Additionally, water vapor sorption tests with further solid characterizations indicated the transformation was faster under higher humidity condition due to the faster nucleation process of cocrystal BAI-NIC. This research not only discovered the mechanism of transformation from coamorphous BAI-NIC to cocrystal form, but also provided an unusual method for cocrystal preparation from its coamorphous form.

Crystallization kinetics and molecular dynamics of binary coamorphous systems of nimesulide and profen analogs

Coamorphous drug delivery systems have emerged as a promising formulation technique for improving the solubility and oral bioavailability of poorly soluble drugs. The selection of a suitable coformer is the key to obtaining a successful coamorphous formulation. This study aims to investigate the impacts of coformers with similar chemical structures but different physical properties on the crystallization behavior and molecular dynamics of binary amorphous systems. The addition of three profen analogs, ibuprofen (IBU), ketoprofen (KETO) and indoprofen (INDO) leads to significantly different effects on the crystallization kinetics of amorphous nimesulide (NIME). The crystal growth rates for amorphous NIME are substantially accelerated in the presence of IBU, but drastically reduced in the presence of INDO, while the incorporation of KETO results in a negligible effect. Broadband dielectric spectroscopy is employed to characterize the molecular dynamics of neat amorphous NIME and coamorphous systems. The addition of three structural analogs alters the molecular mobility of amorphous NIME in different ways, which is consistent with the trend observed for their impacts on the crystallization kinetics, suggesting that the relative mobility between the components of coamorphous mixtures governs the physical stability. In addition, it is found that the temperature dependence of the α-relaxation times for NIME with and without coformers is superimposed once the temperature is scaled by T_g/T, whereas the crystallization kinetics do not overlap on a T_g/T scale. This deviation can result from a complex interplay of thermodynamic and kinetic factors involved in multicomponent amorphous systems. This study provides insights into the crystallization kinetics and molecular dynamics of coamorphous systems containing drug analogs, which can potentially offer more flexibility for the control of physical stability without sacrificing therapeutic efficacy.

Dry and Wet Mechanochemical Synthesis of Piroxicam and Saccharin Co-Crystals and Evaluation by Powder X-Ray Diffraction, Thermal Analysis and Mid- and Near- Infrared Spectroscopy

The purpose of this study is to investigate the effects of dry and wet mechanochemical synthesis on piroxicam (PX) and saccharin (SA) mixtures. For this purpose, PX and SA mixtures prepared by wet mechanochemical processes using three solvents and by dry mechanochemical synthesis were evaluated by mid-and near-infrared spectroscopy, powder X-ray diffraction (PXRD), and differential scanning calorimetry (DSC). The mixtures of wet-type products were transformed into PX/SA 1:1 co-crystals. The effect of the solvent was key to the co-crystallization of PX and SA. The products from the dry process were transformed into the amorphous phase. For the sample of the amorphous mixture, two exothermic peaks due to crystallization were observed in the thermal analysis. Bulk PX was ground for the same number of times for transformation, but was not successfully transformed to the amorphous bulk; the same was observed for SA. It is suggested that the mutual existence of PX and SA promotes mutual amorphization.

How can we improve the physical stability of co-amorphous system containing flutamide and bicalutamide? The case of ternary amorphous solid dispersions

The article describes the preparation and characterization of binary mixtures of two antiandrogens used in prostate cancer treatment, i.e. flutamide (FL) and bicalutamide (BIC), as well as their ternary mixtures with either poly(methyl methacrylate-co-ethyl acrylate) (MMA/EA) or polyvinylpyrrolidone (PVP). The samples were converted into amorphous form to improve their water solubility and dissolution rate. Broadband dielectric spectroscopy and differential scanning calorimetry revealed that FL-BIC (65%) (w/w) does not tend to crystallize from the supercooled liquid state. We made the assumption that the drug-to-drug weight ratio should be maintained as in the case of monotherapy so we decided to investigate the system containing FL and BIC in 15:1 (w/w) ratio with 30% additive of polymers as stabilizers. Our research has shown that only in the case of the FL-BIC-PVP mixture the crystallization has been completely inhibited, both in glassy and supercooled liquid state, which was confirmed by X-ray diffraction studies. In addition, we performed solubility and dissolution rate tests, which showed a significant improvement in solubility of ternary system as compared to its crystalline counterpart. Enhanced physical stability and water solubility of the amorphous ternary system makes it promising for further studies.

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.

How Molecular Mobility, Physical State, and Drug Distribution Influence the Naproxen Release Profile from Different Mesoporous Silica Matrices

Aiming to evaluate how the release profile of naproxen (nap) is influenced by its physical state, molecular mobility, and distribution in the host, this pharmaceutical drug was loaded in three different mesoporous silicas differing in their architecture and surface composition. Unmodified and partially silylated MCM-41 matrices, respectively MCM-41 and MCM-41_sil, and a biphenylene-bridged periodic mesoporous organic matrix, PMO_Bph, were synthetized and used as drug carriers, having comparable pore sizes (∼3 nm) and loading percentages (∼30% w/w). The loaded guest was investigated by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, powder X-ray diffraction (XRD), differential scanning calorimetry (DSC), and dielectric relaxation spectroscopy (DRS). DSC and XRD confirmed amorphization of a nap fraction incorporated inside the pores. A narrower glass transition was detected for PMO_Bph_nap, taken as an indication of the impact of host ordering, which also hinders the guest molecular mobility inside the pores as probed by DRS. While the PMO_Bph matrix is highly hydrophobic, the unmodified MCM-41 readily adsorbs water, accelerating the nap relaxation rate in the respective composite. In the dehydrated state, the faster dynamics was found for the silylated matrix since guest-host hydrogen bond interactions were inhibited to some extent by methylation. Nevertheless, in all the prepared composites, bulk-like crystalline drug deposits outside pores in a greater extent in PMO_Bph_nap. The DRS measurements analyzed in terms of conductivity show that, upon melting, nap easily migrates into pores in MCM-41-based composites, while it stays in the outer surface in the ordered PMO_Bph, determining a faster nap delivery from the latter matrix. On the other side, the mobility enhancement in the hydrated state controls the drug delivery in the unmodified MCM-41 matrix vs the silylated one. Therefore, DRS proved to be a suitable technique to disclose the influence of the ordering of the host surface and its chemical modification on the guest behavior, and, through conductivity depletion, it provides a mean to monitor the guest entrance inside the pores, easily followed even by untrained spectroscopists.

Physicochemical Characterization of a Co-Amorphous Atorvastatin-Irbesartan System with a Potential Application in Fixed-Dose Combination Therapy

The aim of this study was to characterize a 1:1 molar ratio of a pharmacologically relevant co-amorphous atorvastatin-irbesartan (ATR-IRB) system obtained by quench cooling of the crystalline ATR/IRB physical mixture for potential use in the fixed-dose combination therapy. The system was characterized by employing standard differential scanning calorimetry (DSC), Fourier transform-infrared spectroscopy (FT-IR), and intrinsic dissolution rate studies. Quantum mechanical calculations were performed to obtain information regarding intermolecular interactions in the studied co-amorphous ATR-IRB system. The co-amorphous formulation showed a significant improvement in the intrinsic dissolution rate (IDR) of IRB over pure crystalline as well as its amorphous counterpart. An unusual behavior was observed for ATR, as the IDR of ATR in the co-amorphous formulation was slightly lower than that of amorphous ATR alone. Short-term physical aging studies of up to 8 h proved that the ATR-IRB co-amorphous system remained in the amorphous form. Furthermore, no physical aging occurred in the co-amorphous system. FT-IR, density functional theory calculations, and analysis of T_g value of co-amorphous system using the Couchman–Karasz equation revealed the presence of molecular interactions between APIs, which may contribute to the increased physical stability.

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 %.

Pharmaceutical Salts of Enrofloxacin with Organic Acids

Enrofloxacin is a poorly soluble antibacterial drug of the fluoroquinolones class used in veterinary medicine. The main purpose of this work was to investigate the structural and pharmaceutical properties of new enrofloxacin salts. Enrofloxacin anhydrate and its organic salts with tartaric acid, nicotinic acid and suberic acid formed as pure crystalline anhydrous solids. All the crystals were grown from a mixed solution by slow evaporation at room temperature. These products were then characterized by field-emission scanning electron microscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry. Further, X-ray single crystal diffraction analysis was used to study the crystal structure. The intermolecular interactions and packing arrangements in the crystal structures were studied, and the solubility of these salts in water was determined using high-performance liquid chromatography. The results show that the new salts of enrofloxacin developed in this study exhibited excellent water solubility.

Enhanced Physical Stability and Synchronized Release of Febuxostat and Indomethacin in Coamorphous Solids

Coamorphous formulation, a homogeneous monophasic amorphous system composed of multiple components, has been demonstrated as an effective approach for delivering drugs with poor aqueous solubility. In this study, we prepared the coamorphous system composed of two poorly soluble drugs febuxostat (FEB) and indomethacin (IMC) by using cryogenic milling. The combination of these two drugs in the coamorphous form can attain a synergistic effect, especially on gout therapy. Coamorphous solid of FEB and IMC in 1:1 molar ratio exhibited superior physical stability compared with the individual amorphous components, as evidenced by X-ray powder diffractions after 30 days of storage at ambient and elevated temperature. In addition, the FEB-IMC coamorphous system has been demonstrated to show enhanced dissolution performance. The intrinsic dissolution rates of two components in the coamorphous system exhibited the synchronized drug release. Based on the FT-IR spectroscopy, the excellent physical stability and synchronized release of FEB-IMC coamorphous system could be attributed to the heterodimer structure formed by strong hydrogen bonding interactions between these drugs. Furthermore, the supersaturation potential of FEB-IMC coamorphous solids was also investigated through the cosolvent quenching method. The FEB-IMC coamorphous system can effectively inhibit the fast crystallization of FEB in the supersaturated solution. However, the maximum achievable supersaturation of IMC in the coamorphous system decreases to only one fifth of that achieved for the pure amorphous IMC. These results are relevant for understanding the physical stability and complex solution behaviors of the coamorphous formulation.

A novel drug–drug coamorphous system without molecular interactions: improve the physicochemical properties of tadalafil and repaglinide

Tadalafil and repaglinide, categorized as BCS class II drugs, have low oral bioavailabilities due to their poorly aqueous solubilities and dissolutions. The aim of this study was to enhance the dissolution of tadalafil and repaglinide by co-amorphization technology and evaluate the storage and compression stability of such coamorphous system. Based on Flory–Huggins interaction parameter (χ ≤ 0) and Hansen solubility parameter (δ_t ≤ 7 MPa^0.5) calculations, tadalafil and repaglinide was predicted to be well miscible with each other. Coamorphous tadalafil–repaglinide (molar ratio, 1 : 1) was prepared by solvent-evaporation method and characterized with respect to its thermal properties, possible molecular interactions. A single T_g (73.1 °C) observed in DSC and disappearance of crystallinity in PXRD indicated the formation of coamorphous system. Principal component analysis of FTIR in combination with Raman spectroscopy and Ss ¹³C NMR suggested the absence of intermolecular interactions in coamorphous tadalafil–repaglinide. In comparison to pure crystalline forms and their physical mixtures, both drugs in coamorphous system exhibited significant increases in intrinsic dissolution rate (1.5–3-fold) and could maintain supersaturated level for at least 4 hours in non-sink dissolution. In addition, the coamorphous tadalafil–repaglinide showed improved stability compared to the pure amorphous forms under long-term stability and accelerated storage conditions as well as under high compressing pressure. In conclusion, this study showed that co-amorphization technique is a promising approach for improving the dissolution rate of poorly water-soluble drugs and for stabilizing amorphous drugs.

The coamorphous tadalafil–repaglinide (molar ratio, 1 : 1) prepared by solvent-evaporation method significantly improve the physicochemical properties of tadalafil and repaglinide.

Identification and investigation of the vibrational properties of crystalline and co-amorphous drugs with Raman and terahertz spectroscopy

Co-amorphous drugs have shown significant potential in improving the stability and bioavailability compared with single neat amorphous drugs. Here, we explored the molecular interactions of cimetidine, naproxen, indomethacin and their binary co-amorphous mixtures via Raman and terahertz (THz) spectroscopy. We used quench-cooled method to prepare the neat amorphous drugs and their binary co-amorphous mixtures and tested their thermodynamic properties through differential scanning calorimetry (DSC). Then, we found that the stability of co-amorphous drugs was stronger than their neat amorphous components. Furthermore, Raman spectroscopy was used to characterize the vibrational modes between different co-amorphous drugs. Generally, we found that the stability of co-amorphous drugs was better than their neat amorphous components for these samples we tested. Meanwhile, we complemented the detection of THz spectroscopy and found that crystalline and amorphous drugs could be better distinguished.

Fluoroquinolone Amorphous Polymeric Salts and Dispersions for Veterinary Uses

Enrofloxacin (ENRO) is a poorly soluble drug used in veterinary medicine. It differs from the more widely used fluoroquinolone ciprofloxacin (CIP) by the presence of an ethyl substituent on its piperazine amino group. While a number of recent studies have examined amorphous composite formulations of CIP, little research has been conducted with ENRO in this area. Therefore, the main purpose of this work was to produce amorphous solid dispersions (ASDs) of ENRO. The solid-state properties of these samples were investigated and compared to those of the equivalent CIP ASDs, and their water uptake behavior, solubility, dissolution, and antibacterial activity were assessed. Like CIP, X-ray amorphous solid dispersions were obtained when ENRO was ball milled with acidic polymers, whereas the use of neutral polymers resulted in semi-crystalline products. Proton transfer from the carboxylic acids of the polymers to the tertiary amine of ENRO’s piperazine group appears to occur in the ASDs, resulting in an ionic bond between the two components. Therefore, these ASDs can be referred to as amorphous polymeric salts (APSs). The glass transition temperatures of the APSs were significantly higher than that of ENRO, and they were also resistant to crystallization when exposed to high humidity levels. Greater concentrations were achieved with the APSs than the pure drug during solubility and dissolution studies, and this enhancement was sustained for the duration of the experiments. In addition, the antimicrobial activity of ENRO was not affected by APS formation, while the minimum inhibitory concentrations and minimum bactericidal concentrations obtained with the APS containing hydroxypropyl methylcellulose acetate succinate grade MG (HPMCAS-MG) were significantly lower than those of the pure drug. Therefore, APS formation is one method of improving the pharmaceutical properties of this drug.

How can we improve the physical stability of co-amorphous system containing flutamide and bicalutamide? The case of ternary amorphous solid dispersions

The article describes the preparation and characterization of binary mixtures of two antiandrogens used in prostate cancer treatment, i.e. flutamide (FL) and bicalutamide (BIC), as well as their ternary mixtures with either poly(methyl methacrylate-co-ethyl acrylate) (MMA/EA) or polyvinylpyrrolidone (PVP). The samples were converted into amorphous form to improve their water solubility and dissolution rate. Broadband dielectric spectroscopy and differential scanning calorimetry revealed that FL-BIC (65%) (w/w) does not tend to crystallize from the supercooled liquid state. We made the assumption that the drug-to-drug weight ratio should be maintained as in the case of monotherapy so we decided to investigate the system containing FL and BIC in 15:1 (w/w) ratio with 30% additive of polymers as stabilizers. Our research has shown that only in the case of the FL-BIC-PVP mixture the crystallization has been completely inhibited, both in glassy and supercooled liquid state, which was confirmed by X-ray diffraction studies. In addition, we performed solubility and dissolution rate tests, which showed a significant improvement in solubility of ternary system as compared to its crystalline counterpart. Enhanced physical stability and water solubility of the amorphous ternary system makes it promising for further studies.

Transformations between Co-Amorphous and Co-Crystal Systems and Their Influence on the Formation and Physical Stability of Co-Amorphous Systems

The formation of co-amorphous and co-crystal systems are attractive formulation strategies for poorly water-soluble drugs. Intermolecular interactions between the drug and the coformer(s) play an important role in the formation of both systems, making the investigation of transformations between the two systems specifically interesting. The aim of this study thus was to investigate the transformation between the two systems and its influence on the formation and physical stability of co-amorphous systems. Carbamazepine (CBZ) along with benzoic acid, maleic acid, succinic acid, tartaric acid, saccharin, and nicotinamide were used as materials. First, CBZ- co-former co-crystals were prepared. Then the co-crystals and CBZ- co-former physical mixtures were ball milled to investigate the possible co-amorphization process. The XRPD and DSC results showed that CBZ and coformers tended to maintain (co-crystals as the starting material) or form co-crystals (physical mixtures as the starting material), rather than to form co-amorphous systems. Next, co-amorphization from CBZ- co-former physical mixtures via quench cooling was studied. While co-amorphous systems were obtained, the physical stability of these was very low, and the samples recrystallized to either co-crystal forms or the individual components. In conclusion, a possible transformation between the two systems was confirmed, but the resulting co-amorphous systems were highly unstable.

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.

Whey proteins as stabilizers in amorphous solid dispersions

Whey proteins are extensively used as nutritional supplements but have so far not been investigated as co-formers for amorphous solid dispersions (ASD) to enhance the solubility and dissolution rate of poorly water soluble drugs. In this study, whey protein isolate (WPI) and whey protein hydrolysate (WPH) were each mixed with three poorly water soluble drugs (indomethacin: IND, carvedilol: CAR and furosemide: FUR) and prepared as ASDs at 50% (w/w) drug loading using vibrational ball milling. Subsequently, solid state characteristics, dissolution rate and physical stability of the obtained samples were analyzed. All ASDs showed a significant increase in their glass transition temperatures, as well as faster dissolution rates and higher apparent solubilities compared to both the respective pure crystalline and amorphous drugs. The saturation solubility of the drugs was increased in the presence of the whey proteins, and the investigated ASDs showed supersaturation by attaining higher drug concentrations compared to the respective saturation solubilities. Upon storage, ASDs containing IND were found to be physically stable for at least 27 months, whereas, ASDs containing CAR or FUR were stable for about 8 months and 17 months, respectively. This was a tremendous increase in physical stability compared to the pure amorphous drugs which recrystallized within less than one week. Overall, WPI and WPH proved to be promising co-formers and amorphous stabilizers in ASD formulations.

Rational Design of a Famotidine-Ibuprofen Coamorphous System: An Experimental and Theoretical Study

Famotidine (FMT) and ibuprofen (IBU) were used as model drugs to obtain coamorphous systems, where the guanidine moiety of the antacid and the carboxylic group of the nonsteroidal anti-inflammatory drug could potentially participate in H-bonds leading to a given structural motif. The systems were prepared in 3:7, 1:1, and 7:3 FMT and IBU molar ratios, respectively. The latter two became amorphous after 180 min of comilling. FMT-IBU (1:1) exhibited a higher physical stability in assays at 4, 25, and 40 °C up to 60 days. Fourier transform infrared spectroscopy accounted for important modifications in the vibrational behavior of those functional groups, allowing us to ascribe the skill of 1:1 FMT-IBU for remaining amorphous to equimolar interactions between both components. Density functional theory calculations followed by quantum theory of atoms in molecules analysis were then conducted to support the presence of the expected FMT-IBU heterodimer with consequent formation of a R₂²8 structural motif. The electron density (ρ) and its Laplacian (∇²ρ) values suggested a high strength of the specific intermolecular interactions. Molecular dynamics simulations to build an amorphous assembly, followed by radial distribution function analysis on the modeled phase were further employed. The results demonstrate that it is a feasible rational design of a coamorphous system, satisfactorily stabilized by molecular-level interactions leading to the expected motif.

Aspartame as a co-former in co-amorphous systems

Co-amorphous drug delivery systems are a promising approach to improve the dissolution rate and therefore potentially the oral bioavailability of poorly-water soluble drugs. Several low molecular weight excipients, for instance amino acids, have previously been shown to stabilize the amorphous form and increase the dissolution rate of drugs. In this study, the feasibility of aspartame, a methyl ester of the aspartic acid-phenylalanine dipeptide, as a co-former was investigated and compared with the respective single amino acids, both alone and in combination. The poorly water-soluble compounds mebendazole, tadalafil and piroxicam were chosen as model drugs. In contrast to the single amino acids or the physical mixture of both, all drug-aspartame mixtures became amorphous upon 90 min of ball milling. Only a single glass transition temperature (T_g) was detected by modulated differential scanning calorimetry, which indicates that a homogeneous single-phase co-amorphous system was obtained. Powder dissolution tests showed that the dissolution rates of the drugs from drug-aspartame co-amorphous samples were increased compared to crystalline drugs. Furthermore, supersaturation was observed for the mebendazole-aspartame and tadalafil-aspartame co-amorphous systems. In conclusion, aspartame has been shown to be a promising co-former in co-amorphous systems, superior to the single amino acids or their mixtures.

The Role of Glass Transition Temperatures in Coamorphous Drug-Amino Acid Formulations

The improved physical stability associated with coamorphous drug-amino acid (AA) formulations may indicate a decrease in mobility of the amorphous drug molecules, compared to the neat amorphous form of the drug. Since the characteristic glass transition temperatures ( T_gα and T_gβ) represent molecular mobility in amorphous systems, we aimed to characterize T_gα and T_gβ and to determine their role in physical stability as well as their potential usefulness to determine the presence of an excess component (either drug or AA) in coamorphous systems. Indomethacin (IND)-tryptophan (TRP) and carvedilol (CAR)-TRP were used as model coamorphous systems. The analytical techniques used were X-ray powder diffractometry (XRPD) to determine the solid-state form, dynamic mechanical analysis (DMA) to probe T_gα and T_gβ, and differential scanning calorimetry (DSC) to probe thermal behavior of the coamorphous systems. T_gα analysis showed a gradual monotonous increase in T_gα values with increasing AA concentration, and this increase in the T_gα value is not the cause of the improved physical stability. The T_gβ analysis for the IND-TRP sample with 10% drug had a T_gβ of 226.8 K, and samples with 20-90% drug had similar T_gβ values around 212.5 K. For CAR-TRP, samples with 10-40% drug had similar T_gβ values around 230.5 K, and samples with 50-90% drug had similar T_gβ values around 223.3 K. The similar T_gβ values in coamorphous systems at different drug ratios indicate that they in fact are the T_gβ of the component that is in excess to an ideal drug-AA coamorphous mixture. DSC and XRPD analysis showed that for IND-TRP, IND is in excess if the drug concentration is 30% or above and will eventually recrystallize. For CAR-TRP, CAR is in excess and recrystallizes when the drug concentration is 50% or above. We have proposed a means of estimating, on the basis of T_gβ, which drug to AA ratios will lead to optimally physically stable coamorphous systems that can be considered for further development.

Organic acids as co-formers for co-amorphous systems - Influence of variation in molar ratio on the physicochemical properties of the co-amorphous systems

Co-amorphous drug delivery systems are attracting increasing attention in the pharmaceutical field, due to their promising potential to improve the solubility and bioavailability of poorly water-soluble drugs. In this study, three organic acids, namely benzoic acid, malic acid and citric acid, were investigated as co-formers for the weakly basic drug carvedilol. It was hypothesised that the mono-, di- and triprotic nature of the organic acids could result in co-amorphous salt formation with carvedilol at the respective stoichiometric molar ratios, leading to different physicochemical properties of the co-amorphous samples. The carvedilol-organic acid samples were spray dried at molar ratios from 1:4 to 4:1 and amorphous products were obtained for all mixtures except for carvedilol-benzoic acid at a molar ratio of 1:4. A positive deviation of the glass transition temperature compared to the Gordon-Taylor equation was seen for all co-amorphous samples. Salt formation was confirmed by FTIR, but interestingly complete salt formation did not simply follow the molar ratio of the number of basic and acidic groups, most likely due to steric hindrance. As more than one molecule of carvedilol was found to be involved in most co-amorphous systems with the organic acids, this approach allows for a higher "drug loading" compared to other co-formers that usually form co-amorphous systems at a 1:1 M ratio. In addition, the large number of available organic acids offers various options for selecting co-formers.

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.

Influence of Solvent Composition on the Performance of Spray-Dried Co-Amorphous Formulations

Ball-milling is usually used to prepare co-amorphous drug–amino acid (AA) mixtures. In this study, co-amorphous drug–AA mixtures were produced using spray-drying, a scalable industrially preferred preparation method. The influence of the solvent type and solvent composition was investigated. Mixtures of indomethacin (IND) and each of the three AAs arginine, histidine, and lysine were ball-milled and spray-dried at a 1:1 molar ratio, respectively. Spray-drying was performed at different solvent ratios in (a) ethanol and water mixtures and (b) acetone and water mixtures. Different ratios of these solvents were chosen to study the effect of solvent mixtures on co-amorphous formulation. Residual crystallinity, thermal properties, salt/partial salt formation, and powder dissolution profiles of the IND–AA mixtures were investigated and compared to pure crystalline and amorphous IND. It was found that using spray-drying as a preparation method, all IND–AA mixtures could be successfully converted into the respective co-amorphous forms, irrespective of the type of solvent used, but depending on the solvent mixture ratios. Both ball-milled and spray-dried co-amorphous samples showed an enhanced dissolution rate and maintained supersaturation compared to the crystalline and amorphous IND itself. The spray-dried samples resulting in co-amorphous samples were stable for at least seven months of storage.

On the role of salt formation and structural similarity of co-formers in co-amorphous drug delivery systems

Co-amorphous drug delivery systems based on amino acids as co-formers have shown promising potential to improve the solubility and bioavailability of poorly water-soluble drugs. Potential salt formation is assumed to be a key molecular interaction responsible for amorphous stability and increased solubility. However, little is known about the importance of the overall structure of the co-former. In this study, the structurally related amino acids arginine (basic) and citrulline (neutral) were chosen together with four model drugs (acidic furosemide and nitrofurantoin; basic cimetidine and mebendazole) to investigate the importance of salt formation versus structural similarity of co-formers. Drug-amino acid mixtures were ball milled at a molar ratio of 1:1. Generally, arginine showed a higher tendency to successfully form co-amorphous systems with the model drugs compared with citrulline, irrespective of assumed salt formation. Salt forming mixtures showed much higher T_gs, faster dissolution rates, higher solubility and physical stability compared to the corresponding non-salt forming mixtures. In conclusion, structural similarity of the co-formers does not lead to similar co-former performance for a given drug. Salt formation is not a prerequisite for the formation of a co-amorphous system, but if a co-amorphous salt system is formed, improved dissolution rate and physical stability are observed.

Improvement of the physicochemical properties of Co-amorphous naproxen-indomethacin by naproxen-sodium

Improvement of the physicochemical properties of amorphous active pharmaceutical ingredients (APIs) applying the concept of co-amorphisation is a promising alternative to the use of polymer glass solutions. In co-amorphous systems, the physical stability and the dissolution rate of the involved components may be improved in comparison to the respective single amorphous phases. However, for the co-amorphous naproxen-indomethacin model system it has been reported that recrystallization could not be prevented for more than 112days regardless of the applied preparation method and blend ratio In the present study, it was thus tested if the physicochemical properties of co-amorphous naproxen-indomethacin could be optimized by incorporation of the naproxen sodium into the system. Three different co-amorphous systems in nine different molar ratios were prepared by quench-cooling: naproxen-indomethacin (NI), naproxen-sodium-naproxen-indomethacin (NSNI) and naproxen-sodium-indomethacin (NSI). The samples were analyzed by XRPD, FTIR, DSC and by intrinsic dissolution experiments to investigate the influence of naproxen-sodium on the resulting physicochemical properties of the systems. With the three systems, fully amorphous samples with single glass transition temperatures could be prepared with naproxen molar fractions up to 0.7. The NSI and NSNI systems showed up to about 40°C higher Tgs than the NI system. Furthermore, no recrystallization occurred during 270d of storage with the NSI and NSNI samples that were initially amorphous. Moreover, with the NSI system, the intrinsic dissolution rate of naproxen and indomethacin was improved by a factor of 2 compared to the unmodified NI system. In conclusion, the physical stability as well as the dissolution rate was significantly improved if partial or full exchange of naproxen by its sodium salt was performed, which may present a general optimization method to improve co-amorphous systems.

Reactive Melt Extrusion To Improve the Dissolution Performance and Physical Stability of Naproxen Amorphous Solid Dispersions

The purpose of this study was to investigate the reaction between naproxen (NPX) and meglumine (MEG) at elevated temperature and to study the effect of this reaction on the physical stabilities and in vitro drug-release properties of melt-extruded naproxen amorphous solid dispersions (ASDs). Differential scanning calorimetry, hot-stage polarized light microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analyses demonstrated that in situ salt formation with proton transfer between NPX and MEG occurred at elevated temperature during the melt extrusion process. The amorphous NPX-MEG salt was physically most stable when two components were present at a 1:1 molar ratio. Polymeric carriers, including povidone, copovidone, and SOLUPLUS, did not interfere with the reaction between NPX and MEG during melt extrusion. Compared to the traditional NPX ASDs consisting of NPX and polymer only, NPX-MEG ASDs were physically more stable and remained amorphous following four months storage at 40 °C and 75% RH (relative humidity). Based on nonsink dissolution testing and polarized light microscopy analyses, we concluded that the conventional NPX ASDs composed of NPX and polymers failed to improve the NPX dissolution rate due to the rapid recrystallization of NPX in contact with aqueous medium. The dissolution rate of NPX-MEG ASDs was two times greater than the corresponding physical mixtures and conventional NPX ASDs. This study demonstrated that the acid-base reaction between NPX and MEG during melt extrusion significantly improved the physical stability and the dissolution rate of NPX ASDs.

Long-Term Stability of New Co-Amorphous Drug Binary Systems: Study of Glass Transitions as a Function of Composition and Shelf Time

The amorphous state is of particular interest in the pharmaceutical industry due to the higher solubility that amorphous active pharmaceutical ingredients show compared to their respective crystalline forms. Due to their thermodynamic instability, drugs in the amorphous state tend to recrystallize; in order to avoid crystallization, it has been a common strategy to add a second component to hinder the crystalline state and form a thermally stable co-amorphous system, that is to say, an amorphous binary system which retains its amorphous structure. The second component can be a small molecule excipient (such as a sugar or an aminoacid) or a second drug, with the advantage that a second active pharmaceutical ingredient could be used for complementary or combined therapeutic purposes. In most cases, the compositions studied are limited to 1:1, 2:1 and 1:2 molar ratios, leaving a gap of information about phase transitions and stability on the amorphous state in a wider range of compositions. In the present work, a study of novel co–amorphous formulations in which the selection of the active pharmaceutical ingredients was made according to the therapeutic effect is presented. Resistance against crystallization and behavior of glass transition temperature (Tg were studied through calorimetric measurements as a function of composition and shelf time. It was found that binary formulations with Tg temperatures higher than those of pure components presented long-term thermal stability. In addition, significant increments of Tg values, of as much as 15 ∘C, were detected as a result of glass relaxation at room temperature during storage time; this behavior of glass transition has not been previously reported for co-amorphous drugs. Based on these results, it can be concluded that monitoring behavior of Tg and relaxation processes during the first weeks of storage leads to a more objective evaluation of the thermomechanical stability of an amorphous formulation.

Formulation of paracetamol-containing pastilles with in situ coating technology

The focus of this research was to apply the in situ coating technology for producing paracetamol- (PCT-) containing pastilles for paediatric use from a eutectic of two sugar alcohols (sorbitol, xylitol) in one step. This type of melt-technology is more cost-efficient and simpler than other conventional tableting technologies, whereby the formation of the pastilles and their coating occur upon the same fabrication step. We managed to produce pastilles having a softer core and a harder, resistant shell in one cooling step. Adding polyethylene glycol (PEG) 2000 or 6000 to the PCT-containing eutectic, the dissolution rate of PCT could be considerably increased, especially when using PEG 2000, reaching equal dissolution characteristics both under mouth- and gastric-specific conditions. Distributions of the components within the pastilles have been determined by X-ray scattering and Raman spectroscopy. Physico-chemical parameters of the xylitol-sorbitol eutectic and their changes upon adding PCT and PEGs have been determined, and it has been revealed that xylitol and sorbitol form a new entity with a distinguished crystal structure. The significant changes in viscosity were explained and the interaction in the eutectic mixture was investigated using Fourier transform infrared spectroscopy (FT-IR). The uniformity of the physical parameters of the pastilles (including size, weight and drug content) also demonstrates the feasibility of using the cost-efficient and simple one-step eutectic-cooling technology for manufacturing pastilles.

Influence of the cooling rate and the blend ratio on the physical stability of co-amorphous naproxen/indomethacin

Co-amorphization represents a promising approach to increase the physical stability and dissolution rate of amorphous active pharmaceutical ingredients (APIs) as an alternative to polymer glass solutions. For amorphous and co-amorphous systems, it is reported that the preparation method and the blend ratio play major roles with regard to the resulting physical stability. Therefore, in the present study, co-amorphous naproxen-indomethacin (NAP/IND) was prepared by melt-quenching at three different cooling rates and at ten different NAP/IND blend ratios. The samples were analyzed using XRPD and FTIR, both directly after preparation and during storage to investigate their physical stabilities. All cooling methods led to fully amorphous samples, but with significantly different physical stabilities. Samples prepared by fast cooling had a higher degree of crystallinity after 300d of storage than samples prepared by intermediate cooling and slow cooling. Intermediate cooling was subsequently used to prepare co-amorphous NAP/IND at different blend ratios. In a previous study, it was postulated that the equimolar (0.5:0.5) co-amorphous blend of NAP/IND is most stable. However, in the present study the physically most stable blend was found for a NAP/IND ratio of 0.6:0.4, which also represents the eutectic composition of the crystalline NAP/γ-IND system. This indicates that the eutectic point may be of major importance for the stability of binary co-amorphous systems. Slight deviations from the optimal naproxen molar fraction led to significant recrystallization during storage. Either naproxen or γ-indomethacin recrystallized until a naproxen molar fraction of about 0.6 in the residual co-amorphous phase was reached again. In conclusion, the physical stability of co-amorphous NAP/IND may be significantly improved, if suitable preparation conditions and the optimal phase composition are chosen.

Physicochemical Evaluation and Developability Assessment of Co-amorphouses of Low Soluble Drugs and Comparison to the Co-crystals

To judge the developability and analyze functional mechanism of co-amorphouses, we investigated the physicochemical properties of co-amorphouses and compare the properties with the co-crystals having the same drug and counters. Co-amorphous compounds are a novel approach to improve the physicochemical properties of drugs. A co-amorphous is in an amorphous solid state allowing non-ionic interactions between drug molecules and counter molecules. The co-amorphous compounds composed of itraconazole (ITZ) with the organic carboxyl acid, fumaric acid (FA) or L-tartaric acid (TA), were prepared by mechanical grinding. Potential interactions within ITZ-FA co-amorphous were assessed by Raman spectroscopy. ITZ-FA co-amorphous was not crystallized as the co-crystal or as a single ITZ crystal, suggesting that the amorphous state, like the amorphous solid dispersion, was physically stable and that ITZ-FA co-amorphous was also chemically stable. In contrast, no clear interactions were observed within ITZ-TA co-amorphous, and the co-amorphous was physically stable but chemically unstable. The solubility of the co-amorphous state was much higher than those of ITZ crystal and the co-crystals and was almost identical to that of amorphous ITZ. A co-amorphous compound like ITZ-FA co-amorphous might be feasible to implement in the development of solid drug products and bring some merits compared to the co-crystals, and the function is governed by the interaction between a drug and a counter. The co-amorphous approach may be an effective strategy for drug development and can contribute to the production of novel drugs with improved functions.

Structures and physicochemical properties of vortioxetine salts

In the present work, novel salts of the multimodal antidepressant drug vortioxetine (VT) were crystallized with pharmaceutically acceptable acids, aiming to improve the solubility of VT. The acids for VT were selected based on ΔpKabeing greater than 2 or 3. Salts of hydrobromic acid (HBr), hydrochloric acid (HCl),p-hydroxybenzoic acid (PHBA), saccharin (SAC) and L-aspartic acid (ASP) were reported. All salts were characterized by single-crystal X-ray diffraction, FT–IR, powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC). The acidic proton is transferred to the secondary N atom on the piperazine ring of VT, forming the charge-assisted hydrogen bond N+—H...X−(X= Cl, Br, O). Solubility and intrinsic dissolution rate (IDR) experiments were carried out in distilled water (pH = 7.0) to compare the solubilities of the salts with that of VT. The VT–ASP–H2O (1:1:2) salt showed 414 times higher solubility and 1722 times faster IDR compared with VT. VT–ASP–H2O (1:1:2) is a high solubility salt that is stable in a slurry experiment at 298 K in 95% ethanol. The experimental data for the VT–ASP–H2O (1:1:2) salt identify it as a promising drug candidate.

Co-amorphous Formation Induced by Combination of Tranilast and Diphenhydramine Hydrochloride

In this study, we investigated the formation of a co-amorphous system of tranilast (TRL) and diphenhydramine hydrochloride (DPH), which are drugs used for treating allergies and inflammation. The crystallization from undercooled melts of the drugs and drug mixtures was evaluated by thermal analysis. Both drugs in the amorphous state underwent crystallization on heating, although the mixture remained in the amorphous state, indicating the formation of a co-amorphous system. The physicochemical properties of co-amorphous TRL-DPH prepared by the melting-cooling process were studied. The glass transition temperature of co-amorphous TRL-DPH deviated from the theoretical value. The enthalpy relaxation rate of the amorphous drugs, which reflected the molecular mobility, was reduced by the formation of a co-amorphous system. The intermolecular interactions between TRL and DPH in the co-amorphous system were measured by the change in the IR spectra. These results were consistent with the high physical stability. The co-amorphous sample remained in the amorphous state for over 30 days at 40°C, whereas the amorphous drugs showed rapid crystallization. Our findings demonstrate that TRL and DPH form a co-amorphous system, which dramatically decreases their crystallization without an excipient.