Analysis of solid-state transformations of pharmaceutical compounds using vibrational spectroscopy

Solid-state vibrational circular dichroism for pharmaceutical applications: Polymorphs and cocrystal of sofosbuvir

X-ray diffraction is a commonly used technique in the pharmaceutical industry for the determination of the atomic and molecular structure of crystals. However, it is costly, sometimes time-consuming, and it requires a considerable degree of expertise. Vibrational circular dichroism (VCD) spectroscopy resolves these limitations, while also exhibiting substantial sensitivity to subtle modifications in the conformation and molecular packaging in the solid state. This study showcases VCD's ability to differentiate between various crystal structures of the same molecule (polymorphs, cocrystals). We examined the most effective approach for producing high-quality spectra and unveiled the intricate link between structure and spectrum via quantum-chemical computations. We rigorously assessed, using alanine as a model compound, multiple experimental conditions on the resulting VCD spectra, with the aim of proposing an optimal and efficient procedure. The proposed approach, which yields reliable, reproducible, and artifact-free results with maximal signal-to-noise ratio, was then validated using a set comprising of three amino acids (serine, alanine, tyrosine), one hydroxy acid (tartaric acid), and a monosaccharide (ribose) to mimic active pharmaceutical components. Finally, the optimized approach was applied to distinguish three polymorphs of the antiviral drug sofosbuvir and its cocrystal with piperazine. Our results indicate that solid-state VCD is a prompt, cost-effective, and easy-to-use technique to identify crystal structures, demonstrating potential for application in pharmaceuticals. We also adapted the cluster and transfer approach to calculate the spectral properties of molecules in a periodic crystal environment. Our findings demonstrate that this approach reliably produces solid-state VCD spectra of model compounds. Although for large molecules with many atoms per unit cell, such as sofosbuvir, this approach has to be simplified and provides only a qualitative match, spectral calculations, and energy analysis helped us to decipher the observed differences in the experimental spectra of sofosbuvir.

Tale of Two Polymorphs: Investigating the Structural Differences and Dynamic Relationship between Nirmatrelvir Solid Forms (Paxlovid)

Two anhydrous polymorphs of the novel antiviral medicine nirmatrelvir were discovered during the development of Paxlovid, Pfizer's oral Covid-19 treatment. A comprehensive experimental and computational approach was necessary to distinguish the two closely related polymorphs, herein identified as Forms 1 and 4. This approach paired experimental methods, including powder X-ray diffraction and single-crystal X-ray diffraction, solid-state experimental methods, thermal analysis, solid-state nuclear magnetic resonance and Raman spectroscopy with computational investigations comprising crystal structure prediction, Gibbs free energy calculations, and molecular dynamics simulations of the polymorphic transition. Forms 1 and 4 were ultimately determined to be enantiotropically related polymorphs with Form 1 being the stable form above the transition temperature of ∼17 °C and designated as the nominated form for drug development. The work described in this paper shows the importance of using highly specialized orthogonal approaches to elucidate the subtle differences in structure and properties of similar solid-state forms. This synergistic approach allowed for unprecedented speed in bringing Paxlovid to patients in record time amidst the pandemic.

Preparation and Characterization of Lutein Co-Amorphous Formulation with Enhanced Solubility and Dissolution

Lutein is an oxygenated fat-soluble carotenoid and a functional compound with proven health benefits for the human body. Nevertheless, the poor water solubility and low oral bioavailability of lutein greatly limit its application. To address this, we developed an effective approach to enhance the water solubility of lutein through co-amorphous formulation. Specifically, the lutein-sucralose co-amorphous mixture was prepared at a molar ratio of 1:1 using ethanol and water as solvents by employing the solvent evaporation method, followed by solid-state characterization and dissolution testing conducted to assess the properties of the formulation. The X-ray diffraction pattern with an amorphous halo and the differential scanning calorimetry thermogram with no sharp melting peaks confirmed the formation of a binary co-amorphous system. Changes in peak shape, position, and intensity observed in the Fourier transform infrared spectroscopy spectrum revealed intermolecular interactions between lutein and sucralose molecules, while molecular dynamics simulations identified interaction sites between their hydroxyl groups. Additionally, dissolution testing demonstrated better dissolution performance of lutein in the co-amorphous form compared to pure lutein and physical mixture counterparts. Our findings present a novel strategy for improving the water solubility of lutein to make better use of it.

Co-Amorphization of Acemetacin with Basic Amino Acids as Co-Formers for Solubility Improvement and Gastric Ulcer Mitigation

Acemetacin (ACM) is a new non-steroidal anti-inflammatory drug with anti-inflammatory, analgesic, and antipyretic effects. However, the poor water solubility and gastrointestinal side effects limit its use. Recently, the co-amorphous (CAM) strategy has attracted great interest to improve solubility for poorly water-soluble drugs, and basic amino acids have the potential to protect the gastrointestinal tract. In order to develop a highly efficient and low-toxic ACM formulation, we prepared ACM CAM systems, with basic amino acids (lysine, arginine, and histidine) as co-formers, using a cryo-milling method. The solid-state behaviors of the ACM CAM systems were characterized by polarizing light microscopy, differential scanning calorimetry, and powder X-ray diffraction. Fourier transform infrared spectroscopy and molecular docking were carried out to understand the formation mechanism. Moreover, the gastro-protective effects of ACM CAM systems were evaluated in a rat gastric ulcer model. The results demonstrated that the CAM systems improved the dissolution rates of ACM compared with the neat amorphous counterpart. Furthermore, ACM CAM systems are significantly effective in mitigating the ACM-induced gastric ulcer in rats, and the ulcer inhibition rates were almost 90%. More importantly, this study provided a useful method for mitigating drug-induced gastrointestinal damage and broadened the applications of drug-amino acid CAM systems.

Current Applications of Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) in Pharmaceutical Analysis: Review

The present review encompasses various applications of multivariate curve resolution- alternating least squares (MCR-ALS) as a promising data handling, which is issued by analytical techniques in pharmaceutics. It involves different sections starting from a concise theory of MCR-ALS and four detailed applications in drugs analysis. Dissolution, stability, polymorphism, and quantification are the main four detailed applications. The data generated by analytical techniques associated with MCR-ALS deals accurately with different challenges compared to other chemometric tools. For each reviewed purpose, it was explained how MCR-ALS was applied and detailed information was given. Different approaches were introduced to overcome challenges that limit the use of MCR-ALS efficiently in pharmaceutical mixture were also discussed.

Using singular value decomposition to analyze drug/β-cyclodextrin mixtures: insights from X-ray powder diffraction patterns

The article discusses the use of mathematical models and linear algebra to understand the crystalline structures and interconversion pathways of drug complexes with β-cyclodextrin (β-CD). It involved the preparation and analysis of mixtures of indomethacin, diclofenac, famotidine, and cimetidine with β-CD using techniques such as differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), and proton nuclear magnetic resonance (1H-NMR). Singular value decomposition (SVD) analysis is used to identify the presence of different polymorphs in the mixtures of these drugs and β-CD, determine interconversion pathways, and distinguish between different forms. In general, linear algebra or artificial intelligence (AI) is used to approximate the contribution of distinguishable entities to various phenomena. We expected linear algebra to completely reveal all eight entities present in the diffractogram dataset. However, after performing the SVD procedure, we found that only six independent basis functions were extracted, and the entities of the INM α-form and the CIM B-form were not included. It is considered that this is due to that data processing is limited to revealing only six or seven independent factors, as it is a small world. The authors caution that these may not always reproduce or approach reality in complicated real-world situations.

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.

Investigating the function and design of molecular materials through terahertz vibrational spectroscopy

Terahertz spectroscopy has proved to be an essential tool for the study of condensed phase materials. Terahertz spectroscopy probes the low-frequency vibrational dynamics of atoms and molecules, usually in the condensed phase. These nuclear dynamics, which typically involve displacements of entire molecules, have been linked to bulk phenomena ranging from phase transformations to semiconducting efficiency. The terahertz region of the electromagnetic spectrum has historically been referred to as the 'terahertz gap', but this is a misnomer, as there exist a multitude of methods for accessing terahertz frequencies, and now there are cost-effective instruments that have made terahertz studies much more user-friendly. This Review highlights some of the most exciting applications of terahertz vibrational spectroscopy so far, and provides an in-depth overview of the methods of this technique and its utility to the study of the chemical sciences.

Measurement of Moisture Content in Pharmaceutical Tablets by Handheld Near-Infrared Spectrometer: Adopting Quality by Design Approach to Analytical Method Lifecycle Management

Control of moisture content in pharmaceutical solids (raw materials and solid dosage forms) is a challenge to pharmaceutical development and manufacturing. Pharmaceutical solids come in several forms and presentations requiring different, and often lengthy, sample preparation methods for moisture determination. Rapid screening of samples for their moisture content calls for an analytical method that can provide in-situ measurement with no or minimal sample preparation. We presented a near-infrared (NIR) spectroscopic method for rapid and non-destructive measurement of moisture content in a pharmaceutical tablet product. A handheld NIR spectrometer was selected for the quantitative measurement because of its ease of use, low cost, and high signals selective to water absorption in the NIR spectral range. Analytical quality by design (QbD) principles were explored during method design, qualification, and continued performance verification to increase robustness and promote continuous improvement of the analytical procedure. The International Council for harmonization (ICH) Q2 validation criteria were followed for validation of its linearity, range, accuracy, repeatability, intermediate precision, and method robustness. Limit of detection and limit of quantitation were also estimated based on the multivariate nature of the method. Practical considerations were also given to method transfer and a lifecycle approach to implementation of the method.

Characterization of Co-amorphous Carvedilol-Maleic Acid System Prepared by Solvent Evaporation

The aim of this study was to enhance the solubility and stability of the water-insoluble drug carvedilol (CAR) with maleic acid (MLE) to create a co-amorphous system by a solvent evaporation method. Phase diagrams of co-amorphous CAR-MLE, constructed from peak height in the Fourier-transform infrared (FTIR) spectra and the glass transition temperature (Tg) from differential scanning calorimetry (DSC) measurements, revealed that the optimal molar ratio of CAR to MLE was 2:1. The FTIR spectra indicated that the secondary amine-derived peak of CAR and the carboxy group-derived peak of MLE disappeared in the CAR:MLE (2:1) co-amorphous system. DSC measurements showed that the endothermic peaks associated with the melting of CAR and MLE disappeared and a Tg at 43 °C was apparent. Furthermore, the solubility of CAR tested using the shaking flask method for 24 h at 37 °C was 1.2 μg/mL, whereas that of the co-amorphous system was approximately three times higher, at 3.5 μg/mL. Finally, the stability was evaluated by powder- X-ray diffraction at 40 °C; no clear diffraction peaks originating from crystals were observed in the amorphous state until after approximately 3 months of storage. These results indicate that co-amorphization of CAR with MLE improved the solubility of CAR while maintaining its stability in an amorphous form.

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.

Co-amorphous formulation of dipyridamole with p-hydroxybenzoic acid: Underlying molecular mechanisms, physical stability, dissolution behavior and pharmacokinetic study

Coamorphization has been proven to be an effective approach to improve bioavailability of poorly soluble active pharmaceutical ingredients (APIs) by virtue of solubilization, and also contributes to overcome limitation of physical stability associated with amorphous drug alone. In current work, a co-amorphous formulation of dipyridamole (DPM), a poor solubility drug, with p-hydroxybenzoic acid (HBA) was prepared and investigated. At a molar ratio of 1:2, DPM and HBA were melted result in the formation of a binary co-amorphous system. The DPM-HBA co-amorphous was structurally characterized by powder X-ray diffraction (PXRD), temperature modulated differential scanning calorimetry (mDSC), high performance liquid chromatography (HPLC) and solution state ¹H nuclear magnetic resonance (¹H NMR). The molecular mechanisms in the co-amorphous were further analysed via Fourier-transform infrared (FTIR) and Raman spectroscopies, as well as density functional theory (DFT) calculation. All the results consistently revealed the presence of hydrogen bonding interactions between -OH of DPM and -COOH on HBA. Accelerated test and glass transition kinetics showed excellent physical stability of DPM-HBA co-amorphous compared with amorphous DPM along with glass transition temperatures (T_g). The phase-solubility study indicated that complexation occurred between DPM and HBA in solution, which contributed to the solubility and dissolution enhancement of DPM in co-amorphous system. Pharmacokinetic study of co-amorphous DPM-HBA in mouse plasma revealed that the DPM exhibited 1.78-fold and 2.64-fold improvement in AUC_0‑∞ value compared with crystalline and amorphous DPM, respectively. This current study revealed coamorphization is an effective approach for DPM to improve the solubility and biopharmaceutical performance.

Rational Coformer Selection in the Development of 6-Propyl-2-thiouracil Pharmaceutical Cocrystals

Pharmaceutical multicomponent solids have proved to efficiently modulate the physicochemical properties of active pharmaceutical ingredients. In this context, polyphenols are interesting coformers for designing pharmaceutical cocrystals due to their wide safety profile and interesting antioxidant properties. The novel 6-propyl-2-thiouracil multicomponent solids have been obtained by mechanochemical synthesis and fully characterized by powder and single-crystal X-ray diffraction methods. The analysis of supramolecular synthons has been further performed with computational methods, with both results revealing a robust supramolecular organization influenced by the different positions of the hydroxyl groups within the polyphenolic coformers. All novel 6-propyl-2-thiouracil cocrystals show an enhanced solubility profile, but unfortunately, their thermodynamic stability in aqueous media is limited to 24 h.

Effects of Morphology and Solvent/Temperature on THz Spectra: Take Nucleosides as Example

Water molecules were easy to combine with organic molecules and embed into the lattice of solid molecules to form a hydrate. Compared with anhydrous compounds, a hydrate has completely different physical and chemical properties. In this paper, terahertz (THz) spectra of five nucleosides in the solid and liquid phases were studied experimentally by Fourier-transform infrared spectroscopy (FTIR) in the frequency of 0.5-9 THz. In addition, the lattice energy, geometric structure, and vibration spectrum of the molecular crystal of the nucleosides were analyzed theoretically by the generalized energy-based fragmentation approach under periodic boundary conditions (denoted as PBC-GEBF). Furthermore, different nucleoside molecular morphology (monomer, polymer, and crystal), solvent (implicit and explicit water), and temperature/theoretical model effect on the THz spectra were mainly investigated. It was found that in the low-frequency band, the vibrational modes were generally originated from the collective vibration of all molecules involved (more than 99% of them were vibration; only less than 1% of them were rotation and translation), which can reflect the molecular structure and spatial distribution of different substances. The Gibbs free energy of thymidine monomer, dimer, tetramer, and crystal was studied. It was found that the cell-stacking energy had the greatest influence on the spectrum, indicating that only the crystal structure constrained by the periodic boundary conditions could well describe the experimental results. In addition, hydrophobic forces dominated the formation of new chemical bonds and strong inter-molecular interactions; the free water had little contribution to the THz spectrum of nucleosides, while crystalline water had a great influence on the spectrum.

Recrystallization Mediates the Gelation of Amorphous Drugs: The Case of Acemetacin

Amorphization is widely used as an effective method of increasing the solubility of insoluble drugs. However, some amorphous drugs exhibit a much lower dissolution rate than their corresponding crystalline form due to their gelation. In this study, we reported the gels formed from amorphous acemetacin (ACM) for the first time. Gelation was promoted at conditions of lower pH, higher temperature and lower ionic strength. Solid-state characterizations suggested that ACM gels may be formed by recrystallization. This mechanism provides a new direction in facilitating the elimination of gelation for amorphous drugs. Moreover, it also provides the basis for the development of sustained-release formulations using the gelation properties.

19F Solid-state NMR characterization of pharmaceutical solids

Solid-state NMR has been increasingly recognized as a high-resolution and versatile spectroscopic tool to characterize drug substances and products. However, the analysis of pharmaceutical materials is often carried out at natural isotopic abundance and a relatively low drug loading in multi-component systems and therefore suffers from challenges of low sensitivity. The fact that fluorinated therapeutics are well represented in pipeline drugs and commercial products offers an excellent opportunity to utilize fluorine as a molecular probe for pharmaceutical analysis. We aim to review recent advancements of ¹⁹F magic angle spinning NMR methods in modern drug research and development. Applications to polymorph screening at the micromolar level, structural elucidation, and investigation of molecular interactions at the Ångström to submicron resolution in drug delivery, stability, and quality will be discussed.

Comparison of Vibrational Spectroscopic Techniques for Quantification of Water in Natural Deep Eutectic Solvents

Vibrational spectroscopic techniques, i.e., attenuated total reflectance infrared (ATR-IR), near infrared spectroscopy (NIRS) and Raman spectroscopy (RS), coupled with Partial Least Squares Regression (PLSR), were evaluated as cost-effective label-free and reagent-free tools to monitor water content in Levulinic Acid/L-Proline (LALP) (2:1, mol/mol) Natural Deep Eutectic Solvent (NADES). ATR-IR delivered the best outcome of Root Mean Squared Error (RMSE) of Cross-Validation (CV) = 0.27% added water concentration, RMSE of Prediction (P) = 0.27% added water concentration and mean % relative error = 2.59%. Two NIRS instruments (benchtop and handheld) were also compared during the study, respectively yielding RMSECV = 0.35% added water concentration, RMSEP = 0.56% added water concentration and mean % relative error = 5.13% added water concentration, and RMECV = 0.36% added water concentration, RMSEP = 0.68% added water concentration and mean % relative error = 6.23%. RS analysis performed in quartz cuvettes enabled accurate water quantification with RMECV = 0.43% added water concentration, RMSEP = 0.67% added water concentration and mean % relative error = 6.75%. While the vibrational spectroscopic techniques studied have shown high performance in relation to reliable determination of water concentration, their accuracy is most likely related to their sensitivity to detect the LALP compounds in the NADES. For instance, whereas ATR-IR spectra display strong features from water, Levulinic Acid and L-Proline that contribute to the PLSR predictive models constructed, NIRS and RS spectra are respectively dominated by either water or LALP compounds, representing partial molecular information and moderate accuracy compared to ATR-IR. However, while ATR-IR instruments are common in chemistry and physics laboratories, making the technique readily transferable to water quantification in NADES, Raman spectroscopy offers promising potential for future development for in situ, sample withdrawal-free analysis for high throughput and online monitoring.

Towards the Development of Novel Diclofenac Multicomponent Pharmaceutical Solids

Multicomponent pharmaceutical materials offer new opportunities to address drug physicochemical issues and to obtain improved drug formulation, especially on oral administration drugs. This work reports three new multicomponent pharmaceutical crystals of the non-steroidal anti-inflammatory drug diclofenac and the nucleobases adenine, cytosine, and isocytosine. They have been synthesized by mechanochemical methods and been characterized in-depth in solid-state by powder and single crystal X-ray diffraction, as well as other techniques such as thermal analyses and infrared spectroscopy. Stability and solubility tests were also performed on these materials. This work aimed to evaluate the physicochemical properties of these solid forms, which revealed thermal stability improvement. Dissociation of the new phases was observed in water, though. This fact is consistent with the reported observed layered structures and BFDH morphology calculations.

Gelation switch of polyamorphic indomethacin depending on the thermal procedure

Amorphous indomethacin (IMC) prepared under different thermal procedures via melt quenching method showed significantly different dissolution behaviors. This study aims to investigate the influence of thermal procedures on the formation of IMC polyamorphism and to explore the mechanism for their different dissolution behaviors. Amorphous IMC samples were prepared by melting crystalline IMC under a series of temperatures (160-195 °C), respectively, followed by quenching in liquid nitrogen. Samples obtained under 170 °C exhibited bi-halo shapes at ∼15° and ∼26° (2θ), while the ones above 175 °C showed a single halo at ∼21° (2θ), suggesting amorphous IMC prepared under different thermal procedures probably have different local molecular arrangements. In comparison to crystalline IMC, amorphous IMC obtained under 170 °C showed significantly higher dissolution profiles with good dispersibility in aqueous medium, however, all amorphous IMC samples prepared above 175 °C demonstrated much lower dissolution with significant gelation, which seemed like a gelation switch existed for polyamorphic IMC when the preparation temperature was between 170 and 175 °C. Based on physicochemical characterizations, amorphous IMC prepared under 170 °C had higher surface free energy, more surficial hydrophilic groups and better wettability than the ones made above 175 °C. Molecular dynamics simulations revealed that the amorphous samples prepared below 170 °C had similar binding energy values in the range of 310.045-325.479 kcal/mol, while those prepared above 175 °C were significantly lower within 212.193-235.073 kcal/mol. Such binding energy difference might be responsible for their different local molecular arrangements after different thermal procedures. The current study deeply reminds us that the thermal procedure of preparation methods may significantly affect the physicochemical properties of amorphous materials, which should be paid special attention to the polymorphic selection during pharmaceutical development.

Apigenin-oxymatrine binary co-amorphous mixture: Enhanced solubility, bioavailability, and anti-inflammatory effect

Apigenin (APG) is a functional ingredient in many foods, but its poor water solubility results in low bioavailability. This study aimed at delivering APG and improving bioavailability by a food-friendly co-amorphous formulation of APG with oxymatrine (OMT). After preparation of co-amorphous mixture (CM), characterized by powder x-ray diffraction and thermal analysis. Then, the presence of hydrogen bonds was confirmed by vibrational spectroscopy and molecular dynamics simulation. Furthermore, phase solubility and solubility studies, as well as dissolution test indicated that complexation occurred between APG and OMT in solution, which significantly improved the solubility and dissolution of APG-OMT CM. Additionally, pharmacokinetics and biological activity indicated that APG-OMT CM exhibited higher oral bioavailability and anti-inflammatory effect than pure APG. These results suggest that APG-OMT CM may be great potential for application in functional food. Importantly, the study provides a promising delivery system to improve the bioavailability of hydrophobic food ingredients.

(Co-)amorphization of enantiomers - Investigation of the amorphization process, the physical stability and the dissolution behavior

A novel approach for improvement of the aqueous solubility of poorly water soluble compounds applying co-amorphous systems was investigated by application of the enantiomers of the chiral amino acid tryptophan (TRP) as the model system. (Co-)amorphization of various forms of crystalline TRP was achieved by ball milling. Solid state analysis demonstrated significant differences in the amorphization tendency and physical stability between the two TRP enantiomers alone, the TRP racemate and an equimolar physical mixture of D- and L-TRP (TRP conglomerate). Ball milling for 6 h was required to obtain fully amorphous plain D- and L-TRP, whereas the TRP racemate and the TRP conglomerate were transformed into their amorphous forms already within 90 and 60 min of ball milling, respectively. Physical stability of the co-amorphous TRP conglomerate was observed for up to 60 d at ambient conditions as well as 40 °C/0 % RH. In contrast, the amorphous TRP racemate showed a reduced physical stability under ambient conditions. Interestingly, the intrinsic dissolution rates of the amorphous TRP conglomerate and racemate were not higher than those of the respective crystalline forms. In conclusion, applying two enantiomers of a chiral compound may be a promising approach for fast amorphization of an API and for improving the physical stability of the resulting amorphous form.

Design and molecular insights of drug-active metabolite based co-amorphous formulation: A case study of toltrazuril-ponazuril co-amorphous

Co-amorphous supersaturated drug delivery systems are emerging as an alternative strategy to improve the water solubility of BCS II drugs. Typically, the supersaturation and stability of co-amorphous systems largely depend on the type of employed co-former. This study aims to assess the potential for active metabolites of drugs as co-former in drug-drug co-amorphous formulations. Toltrazuril (Tol) was chosen as the model drug, to which ponazuril (Pon) was added as co-former. Considering the importance of intermolecular interactions in co-amorphous systems, we performed highlighted investigations including molecular dynamics simulation and quantum mechanics calculations. The results indicated that Tol and Pon molecules were connected by N-H···O = C hydrogen bonds in the form of a complementary pairing of amide groups. Further, the solubility/dissolution and solid-state stability of the co-amorphous system were investigated. We found that co-amorphous Tol-Pon was stable for at least one month at 40 °C/75% RH, while amorphous materials underwent recrystallization within 10 days. Moreover, both drugs in the co-amorphous system exhibited enhanced "spring parachute effect" during the dissolution process. This could be attributed to the noticeably increased solid-state stabilization as well as inhibition of Pon on the crystallization of Tol from a supersaturated state. In general, our study provides some useful information and molecular insights to guide the development of drug-active metabolite-based co-amorphous formulations.

Solid-state landscape and biopharmaceutical implications of novel metformin-based salts

Three new metformin salts were prepared, allowing the optimization of the drug's pharmaceutical profile and diversifying the API solid-state landscape.

Novel Polymorphic Cocrystals of the Non-Steroidal Anti-Inflammatory Drug Niflumic Acid: Expanding the Pharmaceutical Landscape

Any time the pharmaceutical industry develops a new drug, potential polymorphic events must be thoroughly described, because in a crystalline pharmaceutical solid, different arrangements of the same active pharmaceutical ingredient can yield to very different physicochemical properties that might be crucial for its efficacy, such as dissolution, solubility, or stability. Polymorphism in cocrystal formulation cannot be neglected, either. In this work, two different cocrystal polymorphs of the non-steroidal anti-inflammatory drug niflumic acid and caffeine are reported. They have been synthesized by mechanochemical methods and thoroughly characterized in solid-state by powder and single crystal X-ray diffraction respectively, as well as other techniques such as thermal analyses, infrared spectroscopy and computational methods. Both theoretical and experimental results are in agreement, confirming a conformational polymorphism. The polymorph NIF-CAF Form I exhibits improved solubility and dissolution rate compared to NIF-CAF Form II, although Form II is significantly more stable than Form I. The conditions needed to obtain these polymorphs and their transition have been carefully characterized, revealing an intricate system.

Sensing technologies and experimental platforms for the characterization of advanced oral drug delivery systems

Complex and miniaturized oral drug delivery systems are being developed rapidly for targeted, controlled drug release and improved bioavailability. Standard analytical techniques are widely used to characterize i) drug carrier and active pharmaceutical ingredients before loading into a delivery device (to ensure the solid form), and ii) the entire drug delivery system during the development process. However, in light of the complexity and the size of some of these systems, standard techniques as well as novel sensing technologies and experimental platforms need to be used in tandem. These technologies and platforms are discussed in this review, with a special focus on passive delivery systems in size range from a few 100 µm to a few mm. Challenges associated with characterizing these systems and evaluating their effect on oral drug delivery in the preclinical phase are also discussed.

Multicomponent ionic crystals of diltiazem with dicarboxylic acids toward understanding the structural aspects driving the drug-release

Diltiazem (DIL) is a calcium channel blocker antihypertensive drug commonly used in the treatment of cardiovascular disorders. Due to the high solubility and prompt dissolution of the commercial form hydrochloride (DIL-HCl) that is closely related to short elimination drug half-life, this API is known for exhibiting an unfitted pharmacokinetic profile. In an attempt to understand how engineered multicomponent ionic crystals of DIL with dicarboxylic acids can minimize these undesirable biopharmaceutical attributes, herein, we have focused on the development of less soluble and slower dissolving salt/cocrystal forms. By the traditional solvent evaporation method, two hydrated salts of DIL with succinic and oxalic acids (DIL-SUC-H₂O and DIL-OXA-H₂O), and one salt-cocrystal with fumaric acid (DIL-FUM-H₂FUM) were successfully prepared. An in-depth crystallographic description of these new solid forms was conducted through single and powder X-ray diffraction (SCXRD, PXRD), Hirshfeld surface (HS) analysis, energy framework (EF) calculations, Fourier Transform Infrared (FT-IR) spectroscopy, and thermal analysis (TG, DSC, and HSM). Structurally, the inclusion of dicarboxylic acids in the crystal structures provided the formation of 2D-sheet assemblies, where ionic pairs (DIL⁺/anion^-) are associated with each other via H-bonding. Consequently, a substantial lowering in both solubility (16.5-fold) and intrinsic dissolution rate (13.7-fold) of the API has been achieved compared to that of the hydrochloride salt. These findings demonstrate the enormous potential of these solid forms in preparing of novel modified-release pharmaceutical formulations of DIL.

Comparison of Raman and attenuated total reflectance (ATR) infrared spectroscopy for water quantification in natural deep eutectic solvent

Natural deep eutectic solvents (NADES) are ionic solutions, of great interest for extraction from biomass, biocatalysis, and nanoparticle synthesis. They are easily synthesised and eco-friendly, have low volatility and high dissolution power, and are biodegradable. However, water content in NADES is a critical parameter, affecting their optimal use and extraction efficiency. Vibrational spectroscopic techniques are rapid, label-free, non-destructive, non-invasive, and cost-effective analytical tools that can probe the molecular composition of samples. A direct comparison between a previous study using attenuated total reflectance infrared (ATR-IR) spectroscopy for water quantification in NADES and the same investigation performed with Raman spectroscopy is presently reported. Three NADES systems, namely betaine-glycerol (BG), choline chloride-glycerol (CCG), and glucose-glycerol (GG), containing a range of water concentrations between 0% (w/w) and 40% (w/w), have been analysed with Raman spectroscopy coupled to partial least squares regression multivariate analysis. The values of root mean square error of cross-validation (RMSECV) obtained from analysis performed on the pre-processed spectra over the full spectral range (150-3750 cm^-1) are respectively 0.2966% (w/w), 0.4703% (w/w), and 0.2351% (w/w) for BG, GG, and CCG. While the direct comparison to previous ATR-IR results shows essentially similar outcomes for BG, the RMSECV is 33.14% lower and 65.84% lower for CG and CCG. Furthermore, mean relative errors obtained with Raman spectroscopy, and calculated from a set of samples used as independent samples, were 1.452% (w/w), 1.175% (w/w), and 1.188% (w/w). Ultimately, Raman spectroscopy delivered performances for quantification of water in NADES with similar accuracy to ATR-IR. The present demonstration clearly highlights the potential of Raman spectroscopy to support the development of new analytical protocols in the field of green chemistry.

Exploring two-trace two-dimensional (2T2D) correlation spectroscopy as an effective approach to improve accuracy of discriminant analysis by highlighting asynchronous features in two separate spectra of a sample

This study aims to demonstrate two-trace two-dimensional (2T2D) correlation spectroscopy as an effective tool for improving the accuracy of discriminant analysis. Because 2T2D correlation analysis allows sensitive capturing of asynchronous spectral behaviors between two compared spectra of a sample, the subsequent asynchronous correlation features are expected to reveal more sample-to-sample characteristics and discriminants than the original spectral feature. Initially, near-infrared (NIR) spectroscopic authentication of pure olive oil was performed using the spectra collected at 20 °C and 41 °C. When the 2T2D slice spectra of the samples were used for the discriminant analysis, the authentication accuracy reached to 100%, while became degraded in the cases of using the spectra collected either at 20 °C or 41 °C. Furthermore, a simple strategy of utilizing the average spectrum of one sample group as the reference spectrum in the 2T2D correlation analysis was proposed for two-group discrimination and evaluated for the NIR identification of the geographical origins of agricultural products (milk vetch root (MVR) and perilla seed samples). Because the average spectrum of one sample group was used for comparison, dissimilar constituent compositions of the samples in another group were better observed, thereby improving the accuracy of discrimination of the geographical origins of the samples in both cases. The overall results demonstrated that 2T2D correlation analysis is effective for highlighting the minute asynchronous spectral features of a sample and can be expanded for diverse vibrational spectroscopy-based discriminant analyses.

A New Frontier for Nondestructive Spatial Analysis of Pharmaceutical Solid Dosage Forms: Spatially Offset Low-Frequency Raman Spectroscopy

A new Raman subtechnique, spatially offset low-frequency Raman spectroscopy (SOLFRS), is demonstrated via an analysis of pharmaceutical solid dosage forms. Several different model systems comprised of celecoxib (a popular anti-inflammatory drug), α-lactose anhydrous stable form, α-lactose monohydrate, and polyvinylpyrrolidone (PVP) were used to represent tangible scenarios for the application of SOLFRS. Additionally, the challenges and limitations were highlighted in relation to its real-time use, and potential solutions to address them were also provided. Lastly, the future directions for this new variation of Raman spectroscopic technique were briefly discussed, including its potential for broader application in pharmaceutical analysis and other research fields.

Novel solid forms of insomnia drug suvorexant with improved solubility and dissolution: accessing salts from a salt solvate route

Suvorexant (SRX) is a dual orexin receptor antagonist used for the treatment of insomnia.

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.

Co-electrospraying technology as a novel approach for dry powder inhalation formulation of montelukast and budesonide for pulmonary co-delivery

In the current study electrospraying methodology was used for particle engineering of montelukast and budesonide to prepare a combined inhalable dry powder formulation applicable as a smart regimen in asthma treatment. For this, electrospraying was carried out using different solvents and drug concentrations. No carrier was added for the formulation of montelukast-budesonide combination as montelukast played the role of both active ingredient and carrier. Scanning electron microscopy, particle size analysis, gas chromatography, powder X-ray diffraction, Fourier transform infrared spectroscopy, and differential scanning calorimetry were used to evaluate the physicochemical properties of the produced drug particles. In vitro drug deposition pattern was assessed using next generation impactor, and the dissolution profile of the selected formulations was characterized via modified diffusion franz cell method. The FPF value for the co-electrosprayed carrier free formulation of montelukast-budesonide was 38% with a significantly enhanced dissolution rate for budesonide compared to the budesonide alone formulations. The pharmacological effects of hypothesized combined formulation was assessed by measuring its power to inhibit the production of reactive oxygen species in human normal lung cells. The results showed that the combination of montelukast and budesonide can exert a synergistic effect. The findings in the current study emphasize that using montelukast as a carrier for budesonide not only has greatly improved the aerosolization behavior and dissolution rate of budesonide but also has resulted in synergistic pharmacological effects, indicating the suitability of this combination as an anti-asthmatic therapeutic.

Quantitative analysis of solid dosage forms of cefixime using Raman spectroscopy

Quantification of antibiotics is of significant importance because of their use in the prevention and treatment of different diseases. Cefixime (CEF) is a cephalosporin antibiotic that is used against bacterial infections. In the present study, Raman spectroscopy has been applied for the identification and quantification of Raman spectral features of cefixime with different concentrations of Active Pharmaceutical Ingredient (API) and excipients in solid dosage forms. The changes in Raman spectral features of API and excipients in the solid dosage forms of cefixime were studied and Raman peaks were assigned based on the literature. Multivariate data analysis techniques including the Principal Component Analysis (PCA) and Partial Least Squares Regression analysis (PLSR) have been performed for the qualitative and quantitative analysis of solid dosage forms of cefixime. PCA was found helpful in differentiating all the Raman spectral data associated with the different solid dosage forms of cefixime. The coefficient of determination (R²), mean absolute error (MAE), and mean relative error (MRE) for the calibration data-set were 0.99, 0.72, and 0.01 respectively and for the validation data-set were 0.99, 3.15, and 0.02 respectively, that shows the performance of the model. The root mean square error of calibration (RMSEC) and root mean square error of prediction (RMSEP) were found to be 0.56 mg and 3.13 mg respectively.

Enhancing the solubility and permeability of the diuretic drug furosemide via multicomponent crystal forms

Furosemide (FSM) is a biopharmaceutical classification system (BCS) class IV drug, being a potent loop diuretic used in the treatment of congestive heart failure and edema. Due to its low solubility and permeability, FSM is known for exhibiting poor oral bioavailability. In order to overcome or even minimize these undesirable biopharmaceutical attributes, in this work we have focused on the development of more soluble and permeable multicomponent solid forms of FSM. Using solvent evaporation as crystallization method, a salt and a cocrystal of FSM with imidazole (IMI) and 5-fluorocytosine (5FC) coformers, named FSM-IMI and FSM-5FC, respectively, were successfully prepared. A detailed structural study of these new solid forms was conducted using single and powder X-ray diffraction (SCXRD, PXRD), Fourier Transform Infrared (FT-IR) and proton Nuclear Magnetic Resonance (¹H NMR) spectroscopy and thermal analysis (thermogravimetry, differential scanning calorimetry and hot-stage microscopy). Both FSM-IMI and FSM-5FC showed substantial enhancements in the solubility (up 118-fold), intrinsic dissolution (from 1.3 to 2.6-fold) and permeability (from 2.1 to 2.8-fold), when compared to the pure FSM. These results demonstrate the potential of these new solid forms to increase the limited bioavailability of FSM.

Stochastic Differential Scanning Calorimetry by Nonlinear Optical Microscopy

Stochastic phase transformations within individual crystalline particles were recorded by integration of second harmonic generation (SHG) imaging with differential scanning calorimetry (DSC). The SHG activity of a crystal is highly sensitive to the specific molecular packing arrangement within a noncentrosymmetric lattice, providing access to information otherwise unavailable by conventional imaging approaches. Consequently, lattice transformations associated with dehydration/desolvation events were readily observed by SHG imaging and directly correlated to the phase transformations detected by the DSC measurements. Following studies of a model system (urea), stochastic differential scanning calorimetry (SDSC) was performed on trehalose dihydrate, which has a more complex phase behavior. From these measurements, SDSC revealed a broad diversity of single-particle thermal trajectories and direct evidence of a "cold phase transformation" process not observable by the DSC measurements alone.

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.

Polyelectrolytes in Hot Melt Extrusion: A Combined Solvent-Based and Interacting Additive Technique for Solid Dispersions

Solid dispersions are important supersaturating formulations to orally deliver poorly water-soluble drugs. A most important process technique is hot melt extrusion but process requirements limit the choice of suitable polymers. One way around this limitation is to synthesize new polymers. However, their disadvantage is that they require toxicological qualification and present regulatory hurdles for their market authorization. Therefore, this study follows an alternative approach, where new polymeric matrices are created by combining a known polymer, small molecular additives, and an initial solvent-based process step. The polyelectrolyte, carboxymethylcellulose sodium (NaCMC), was tested in combination with different additives such as amino acids, meglumine, trometamol, and urea. It was possible to obtain a new polyelectrolyte matrix that was viable for manufacturing by hot melt extrusion. The amount of additives had to be carefully tuned to obtain an amorphous polymer matrix. This was achieved by probing the matrix using several analytical techniques, such as Fourier transform infrared spectroscopy, differential scanning calorimetry, hot stage microscopy, and X-ray powder diffraction. Next, the obtained matrices had to be examined to ensure the homogeneous distribution of the components and the possible residual crystallinity. As this analysis requires probing a sample on several points and relies on high quality data, X-ray diffraction and starring techniques at a synchrotron source had to be used. Particularly promising with NaCMC was the addition of lysine as well as meglumine. Further research is needed to harness the novel matrix with drugs in amorphous formulations.

Effects of Temperature and Ionic Strength of Dissolution Medium on the Gelation of Amorphous Lurasidone Hydrochloride

PURPOSE

Amorphous lurasidone hydrochloride (LH) showed decreased dissolution behavior in comparison to crystalline LH owing to gelation during dissolution as reported in our previous study. The current study aims to investigate external factors including temperature and ionic strength on the gelation and hence the dissolution of amorphous LH.

METHODS

Dissolution tests of amorphous LH were performed under different temperatures and buffer ionic strengths. The formed gels were characterized by rheology study, texture analysis, PLM, SEM, DSC, XRPD and FTIR.

RESULTS

With the increase of temperature and ionic strength of medium, the dissolution of amorphous LH decreased, while the strength, hardness and adhesiveness of in situ formed gel enhanced. Amorphous LH converted into its crystalline state during dissolution and the crystallization rate was affected by medium conditions. With medium temperature increasing from 30°C to 45°C, the gel microstructure changed from interconnecting fibrillar network to spherical particle aggregate. On the other hand, the formed spherulitic gel aggregate exhibited increased particle size when increasing the ionic strength of medium.

CONCLUSIONS

With increase of temperature and ionic strength, the gel strength of in situ formed gel from amorphous LH enhanced with more compact microstructure, subsequently leading to decreased dissolution profiles.