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

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

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

Eco-Friendly high Drug-Loading microemulsions with Incorporation of Deep eutectic Solvents: Advancing precision with the dual Ouzo effect

Deep eutectic solvents (DES) enhance drug solubility but require delivery systems, while the Ouzo effect enables surfactant-free microemulsion formation despite limitations in oil phase ratio. By integrating DES as the oil phase, this study develops a dual Ouzo effect microemulsion system that induces both microemulsions and nanoprecipitations simultaneously. Through detailed analysis of composition diagrams, precise adjustment of the mass ratio of VA64 to propylene glycol enables strict control over particle size from 200 nm to 550 nm. This approach enhanced curcumin's solubility to 17.11 mg/mL, a 1700-fold increase compared to its water solubility, with excellent stability showing only 22.4 % degradation after 4 h of light exposure (versus 90-95 % in conventional carriers). The system increased the cumulative release amount of curcumin and presented a rapid initial release followed by a sustained release. Compared with traditional Ouzo effect systems, introducing DES significantly increased the oil phase ratio from 0.05 % to 30 % through enhanced molecular interactions and supersaturation. DES composition adjustment enabled microemulsion stabilization without complex processing, achieving optimal stability with a three-phase contact angle of 89.2° (±0.3°), approaching the theoretical ideal value of 90° for interface stability.

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

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

Creation of Long-Term Physical Stability of Amorphous Solid Dispersions N-Butyl-N-methyl-1-phenylpyrrolo[1,2-a]pyrazine-3-carboxamide, Resistant to Recrystallization Caused by Exposure to Moisture

Amorphous solid dispersion (ASD) technology is often used as a promising strategy to improve the solubility of active pharmaceutical ingredients (APIs). ASDs allow APIs to be dispersed at the molecular level in a polymer carrier, destroying the crystalline structure of the APIs and, thanks to the polymer, providing long-term supersaturation in solution. However, stability issues are an obstacle to the development of new medications with ASD. In addition to the molecular mobility at elevated temperatures leading to the crystallization of APIs, moisture affects the physical stability of ASD, leading to fractional separation and recrystallization. N-butyl-N-methyl-1-phenylpyrrolo[1,2-a]pyrazine-3-carboxamide (GML-3) is an original API with both anxiolytic and antidepressant activity, but its insolubility in water can negatively affect (influence) bioavailability. Our study aims to create ASD GML-3 with moisture-resistant polymers (Soluplus®, HPC) and assess the stability of the amorphous state of ASD after storage in high humidity conditions. As a result, HPC KlucelTM FX was revealed to be more stable than the brand, providing a high level of API release into the purified water environment and stability after 21 days (3 weeks) of storage in high humidity conditions.

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

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

The Enhanced Skin Permeation of Flavonoids Via the Application of a Coamorphous in a Microemulsion Formulation

Improving the permeability and solubility of poorly water-soluble compounds is a major difficulty in skin permeation. In this study, we investigated whether using a pharmaceutical technique such as applying coamorphous to a microemulsion enhances the skin permeation of polyphenolic compounds. The melt-quenching technique created the coamorphous system between naringenin (NRG) and hesperetin (HPT), two polyphenolic compounds with poor water solubility. By creating a supersaturated state, the aqueous solution of coamorphous NRG/HPT demonstrated improved NRG and HPT skin permeation. However, as both compounds precipitated, the supersaturation ratio decreased. In contrast to crystal compounds, incorporating coamorphous material into microemulsions enabled the preparation of microemulsions in a wider formulation range. Additionally, compared to microemulsions with crystal compounds and an aqueous suspension of coamorphous, microemulsions with coamorphous NRG/HPT increased skin permeation of both compounds by more than four times. These results suggested that interactions between NRG and HPT are maintained in the microemulsion and enhance both compounds' skin permeation. An approach for improving the skin permeation of poorly water-soluble chemicals would be to apply a coamorphous system to a microemulsion.

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

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

Supersaturation and Precipitation Applicated in Drug Delivery Systems: Development Strategies and Evaluation Approaches

Supersaturation is a promising strategy to improve gastrointestinal absorption of poorly water-soluble drugs. Supersaturation is a metastable state and therefore dissolved drugs often quickly precipitate again. Precipitation inhibitors can prolong the metastable state. Supersaturating drug delivery systems (SDDS) are commonly formulated with precipitation inhibitors, hence the supersaturation is effectively prolonged for absorption, leading to improved bioavailability. This review summarizes the theory of and systemic insight into supersaturation, with the emphasis on biopharmaceutical aspects. Supersaturation research has developed from the generation of supersaturation (pH-shift, prodrug and SDDS) and the inhibition of precipitation (the mechanism of precipitation, the character of precipitation inhibitors and screening precipitation inhibitors). Then, the evaluation approaches to SDDS are discussed, including in vitro, in vivo and in silico studies and in vitro-in vivo correlations. In vitro aspects involve biorelevant medium, biomimetic apparatus and characterization instruments; in vivo aspects involve oral absorption, intestinal perfusion and intestinal content aspiration and in silico aspects involve molecular dynamics simulation and pharmacokinetic simulation. More physiological data of in vitro studies should be taken into account to simulate the in vivo environment. The supersaturation theory should be further completed, especially with regard to physiological conditions.

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.