Development and In Vitro Evaluation of a Deep Eutectic System to Improve Cefuroxime Axetil Solubility by Enhancing the Dissolution

Abstract

Poor aqueous solubility remains a principal barrier to oral delivery of many drugs, including cefuroxime axetil (CA). Cefuroxime Axetil (CA), a second-generation cephalosporin prodrug, exhibits poor aqueous solubility and low oral bioavailability due to its high lipophilicity and crystalline nature. As a Biopharmaceutics Classification System (BCS) Class II drug, its therapeutic efficacy is largely limited by its dissolution rate, necessitating advanced formulation strategies to enhance solubility. Traditional techniques such as solid dispersions, complexation, and lipid-based systems have shown partial success but often involve high energy consumption or the use of toxic solvents. This review focuses on the role of DES in enhancing the solubility and dissolution of Cefuroxime Axetil by discussing their mechanisms, types (choline chloride-based, NADES, THEDES), formulation methods, and in vitro evaluation techniques, including solubility, dissolution, and characterisation studies. A eutectic system or eutectic mixture is a type of homogeneous mixture that has a melting point lower than that of the constituents. The lowest possible melting point over all of the mixing ratios of the constituents is called the eutectic temperature. DESs were prepared by combining choline chloride (HBA) with various hydrogen bond donors (HBDs) such as glycerol, lactic acid, and urea in different molar ratios. Choline chloride (CHCL), commonly used as a hydrogen bond acceptor (HBA), forms deep eutectic solvents (DESs) when combined with various hydrogen bond donors (HBDs). For example, ChCl (melting point 303°C) and urea (134°C) form a DES at a mole ratio of 1:2, with a eutectic point of 12°C. Drug–DES mixtures were formulated by the solvent evaporation method and characterised for physicochemical compatibility (FTIR), crystallinity (DSC, PXRD), morphology (SEM), and thermal stability (TGA). The solubility of CA was evaluated in water and simulated gastrointestinal fluids, and in vitro dissolution studies were performed using a USP Type II apparatus. Among all DES formulations, choline chloride–glycerol (1:2) showed the greatest solubility enhancement and achieved more than 85% drug release within 30 minutes, compared to only 35% from pure CA. The improved dissolution is attributed to the hydrogen bonding and partial amorphisation of CA within the DES matrix. The study concludes that DES-based systems represent a promising, cost-effective, and environmentally benign strategy for improving solubility and dissolution of poorly water-soluble drugs like CA, with potential to enhance oral bioavailability.

Keywords

Dissolution, cefuroxime axetil, deep eutectic solvent mixture. solubility enhancement, hydrogen bonding, amorphisation

Introduction

Physicochemical Properties of Cefuroxime Axetil Cause Solubility Challenges

The poor aqueous solubility of Cefuroxime Axetil (CA) is primarily attributed to its physicochemical characteristics, including its crystalline structure, hydrophobic functional groups, and lipophilic prodrug nature. These intrinsic properties directly influence the dissolution behaviour of the drug in biological fluids, thereby affecting its bioavailability and therapeutic performance (31).

1. Crystalline Nature and Strong Intermolecular Bonding

Cefuroxime Axetil exists in a highly crystalline form, stabilised by strong intermolecular hydrogen bonding and van der Waals interactions. These strong lattice forces make it energetically unfavourable for the crystal structure to disintegrate into individual molecules during dissolution (32). Consequently, the drug dissolves very slowly in aqueous media, as substantial energy is required to break these intermolecular interactions. Crystalline drugs typically show lower solubility and slower dissolution rates than their amorphous counterparts (33).

2. Lipophilic and Ester Functional Groups

Cefuroxime Axetil is an ester prodrug of the hydrophilic parent drug, Cefuroxime, designed to improve membrane permeability. However, the introduction of lipophilic axetil moieties increases the compound’s hydrophobic character and reduces its polarity, resulting in very low aqueous solubility (~0.1 mg/mL at 25 °C) (34). These nonpolar regions resist interaction with water molecules, hindering the solvation process necessary for dissolution (35).

3. Poor Wetting and High Interfacial Tension

Due to its hydrophobic surface properties, Cefuroxime Axetil exhibits poor wettability in aqueous media. The drug particles tend to aggregate rather than disperse when in contact with water, leading to reduced surface area exposure and slower dissolution (36). This property further limits the rate at which the drug becomes available for absorption in the gastrointestinal tract.

4. Instability in Aqueous Environment

Cefuroxime Axetil is also chemically unstable in aqueous environments, particularly under acidic or basic conditions, where it undergoes hydrolysis to Cefuroxime before absorption (37). This instability complicates formulation efforts, as improving solubility in water may simultaneously lead to degradation, reducing the available active drug concentration.

5. High Partition Coefficient (log P)

The lipophilic nature of Cefuroxime Axetil is reflected in its relatively high log P value, indicating a preference for lipid over aqueous environments. While this favors membrane permeability, it adversely affects dissolution in gastrointestinal fluids, where water is the primary medium. Thus, there exists a trade-off between permeability and solubility, which is a hallmark challenge for BCS Class II drugs like Cefuroxime Axetil (38).

Solubility and Bioavailability Challenges

Several intrinsic physicochemical factors are responsible for this limited solubility.

1. Crystalline Structure and Strong Lattice Energy

Cefuroxime Axetil exists in a crystalline solid form, characterised by strong intermolecular hydrogen bonding and van der Waals interactions between its molecules. This tight crystal lattice requires a significant amount of energy to disrupt during dissolution (39). Drugs with high lattice energy, such as CA, tend to have low aqueous solubility because water molecules cannot easily penetrate and separate the crystalline layers.

2. Lipophilic Nature and Presence of Ester Moiety

Cefuroxime Axetil is an ester prodrug of the hydrophilic parent compound Cefuroxime. The axetil esterification increases the molecule’s lipophilicity (log P ≈ 2.6), which enhances permeability through biological membranes but drastically reduces solubility in water (40). The hydrophobic axetil group resists interaction with polar water molecules, preventing effective solvation and dissolution (41).

3. Poor Wettability

Due to its hydrophobic surface characteristics, CA particles exhibit poor wettability in aqueous environments. When introduced into water, the drug particles tend to aggregate instead of dispersing uniformly, reducing the available surface area for dissolution. This poor wetting behaviour further slows down the dissolution rate (42).

4. Instability in Aqueous Media

Cefuroxime Axetil is chemically unstable in water, undergoing hydrolysis to its parent compound, Cefuroxime, before absorption can occur (43). This instability complicates formulation efforts, as enhancing solubility often accelerates degradation, leading to loss of active drug before it can be absorbed.

5. Limited Hydrogen Bonding with Water

The molecular structure of CA contains several nonpolar regions, limiting its ability to form hydrogen bonds with water molecules. Since hydrogen bonding is a key driver of solubility for polar drugs, this structural feature further reduces CA’s solubility in aqueous media (44).

6. Biopharmaceutics Classification

According to the Biopharmaceutics Classification System (BCS), Cefuroxime Axetil is categorised as a Class II drug — characterised by low solubility and high permeability (45). For these drugs, the dissolution rate becomes the rate-limiting step for absorption, meaning that poor solubility directly limits oral bioavailability.

Solubility Enhancement Methods

Enhancing the solubility and dissolution rate of poorly water-soluble drugs like Cefuroxime Axetil is a critical step in improving their oral bioavailability and therapeutic performance. Over the years, several conventional formulation strategies have been developed to address this issue. Among the most effective and widely used techniques are solid dispersions, complexation with cyclodextrins, lipid-based formulations, and nanosuspensions.

1. Solid Dispersions

Solid dispersion (SD) involves dispersing a poorly soluble drug in a hydrophilic carrier matrix to enhance its solubility and dissolution rate. The drug is molecularly dispersed or finely distributed within the carrier, leading to:

• Increased surface area,
• Improved wettability
• Reduced particle size, and
• Transformation of the drug from crystalline to amorphous form, which is more soluble.
• Common carriers include polyethene glycol (PEG), polyvinylpyrrolidone (PVP), and hydroxypropyl methylcellulose (HPMC). (46).

2. Complexation with Cyclodextrins

Cyclodextrins (CDs) are cyclic oligosaccharides capable of forming inclusion complexes with hydrophobic drug molecules. The hydrophobic cavity of CDs encapsulates the non-polar portion of the drug, while the hydrophilic exterior interacts with water, thereby increasing apparent solubility. (47,48).

3. Lipid-Based Formulations

Lipid-based systems (such as self-emulsifying drug delivery systems (SEDDS) and liposomes) enhance solubility by dissolving the drug in lipidic excipients. These systems promote micellar solubilization and facilitate lymphatic transport, bypassing hepatic first-pass metabolism. (49).

4. Nanosuspensions

A nanosuspension is a colloidal dispersion of drug nanoparticles stabilised by surfactants. Reducing the particle size to the nanometre range increases surface area and dissolution velocity according to the Noyes–Whitney equation. Furthermore, nanoparticles can improve drug permeability across biological membranes. (50).

Deep Eutectic Systems (DES):

Deep Eutectic Systems (DES) are novel liquid systems formed by mixing two or more solid components, typically a hydrogen bond donor (HBD) and a hydrogen bond acceptor (HBA), which interact through hydrogen bonding to form a eutectic mixture with a melting point significantly lower than that of the individual components (51). These systems were first introduced by Abbott and co-workers in 2003 as an alternative to ionic liquids (ILs) due to their biocompatibility, biodegradability, cost-effectiveness, and ease of preparation. Unlike conventional solvents, DESs are often composed of naturally derived, non-toxic materials, making them especially suitable for pharmaceutical and biomedical applications. A typical example of a DES is the combination of choline chloride (HBA) with urea (HBD) in a 1:2 molar ratio, which produces a clear liquid at room temperature even though both components are solid individually.

Types of Deep Eutectic Systems (DES)

Deep eutectic systems (DES) can be categorised based on the nature and purpose of their components. In the pharmaceutical field, three major types are of particular relevance: Choline chloride-based DES, Natural Deep Eutectic Solvents (NADES), and Therapeutic Deep Eutectic Solvents (THEDES). Each class exhibits unique physicochemical and biological properties that influence its suitability for solubility enhancement, drug delivery, and formulation development.

1. Choline Chloride-Based Deep Eutectic Systems

Choline chloride-based DES are the earliest and most commonly studied systems. They are typically composed of choline chloride (ChCl) as the hydrogen bond acceptor (HBA) and compounds such as urea, glycerol, ethylene glycol, or organic acids as hydrogen bond donors (HBDs). These combinations interact through hydrogen bonding to form a liquid at room temperature, even though the individual components are solid.

Choline chloride is biodegradable, non-toxic, and inexpensive, making it highly suitable for pharmaceutical applications. Such DESs effectively improve the solubility and stability of hydrophobic drugs due to enhanced hydrogen bonding and polarity.

Example systems:

• ChCl : Urea (1:2)
• ChCl : Glycerol (1:2)
• ChCl : Citric acid (1:1)

Applications:

Used for improving drug solubility, bioavailability, and dissolution rate of poorly soluble compounds, including ibuprofen, ketoprofen, and cefuroxime axetil. (52)

2. Natural Deep Eutectic Solvents (NADES)

Natural deep eutectic solvents (NADES) are formed from naturally occurring primary metabolites, such as sugars, amino acids, organic acids, and polyols. They are biocompatible, biodegradable, and environmentally sustainable, offering an eco-friendly alternative to synthetic solvents. These solvents mimic the natural intracellular environment and have been shown to enhance solubility, stability, and bioavailability of both hydrophilic and hydrophobic drugs. NADES are particularly advantageous for pharmaceutical, nutraceutical, and cosmetic formulations.

Example systems:

• Choline chloride: Glucose (1:1)
• Lactic acid: Glucose (5:1)
• Proline: Malic acid (1:1)

Applications:

NADES are used for solubilizing poorly water-soluble drugs, stabilizing biomolecules, and extracting natural compounds. (53)

3. Therapeutic Deep Eutectic Solvents (THEDES)

Therapeutic deep eutectic solvents (THEDES) are an innovative subclass of DES in which one or more components are active pharmaceutical ingredients (APIs). In THEDES, the drug itself participates in hydrogen bonding as an HBD or HBA, forming a eutectic mixture with enhanced solubility and stability. This approach allows THEDES to serve both as a solvent and as an active drug delivery medium, leading to improved bioavailability, permeability, and controlled release.

Example systems:

• Lidocaine: Ibuprofen (1:1)
• Menthol: Camphor (1:1)
• Choline chloride: Malonic acid: Cefuroxime Axetil (1:1:1)

Applications:

THEDES are applied in transdermal drug delivery, oral formulations, and co-delivery systems, offering synergistic therapeutic effects and improved drug solubilization.(54,55)

Mechanisms of Solubility & Dissolution Enhancement by DES

1. Hydrogen-bonding/interaction effects

DESs provide an environment rich in hydrogen-bond donor and acceptor sites. These may interact with drug molecules (e.g., via H-bonding to polar/ionisable groups or via van der Waals/hydrophobic interactions), thereby stabilising the drug in solution and disrupting the solid-state crystalline lattice. For example, one review reports that the strong hydrogen bonding and van der Waals interactions within DESs reduce the lattice energy of the API, thereby facilitating dissolution and enhancing solubility. (56)

2. Disruption of crystallinity/amorphisation

By dissolving or partially solubilising the drug in the DES medium, or forming a drug-DES complex/interaction, the crystalline lattice energy barrier is reduced (or the drug exists in a partly amorphous form). This improves dissolution kinetics. Reviews catch this as one of the major mechanisms. (57)

3. Tenable solvent polarity, viscosity, microenvironment

DESs can be designed by varying the HBA/HBD ratio, incorporating water or co-solvents, adjusting temperature, etc. This tunability means one can tailor the medium to better solvate a given drug. For example, increasing water content may shift the optimum composition for solubility. (58) On the flip side, high viscosity of DES can impose limitations on mass-transfer/diffusion and hence dissolution rate.

4. Supersaturation/dissolution enhancement effect

When a drug is delivered in a DES or DES-based medium, once diluted (e.g., by gastrointestinal fluids), a supersaturated state may be created (i.e., concentration above equilibrium solubility), thereby enhancing the driving force for absorption. Some reviews consider DES as “supersaturating systems”. (59)

5. Permeability/absorption benefits

Beyond solubility/dissolution, some studies indicate that DESs may enhance drug permeability or absorption (through modulation of membrane interactions or via improved solubilisation). For example, in one formulation of a DES with Celecoxib, both in vitro and in vivo absorption benefits were shown. (60)

Evaluation Parameters for DES-Based Drug Formulations

The development of Deep Eutectic Systems (DES) for enhancing the solubility and dissolution of poorly soluble drugs requires systematic in vitro evaluation to establish their effectiveness, stability, and underlying interaction mechanisms. The following analytical and performance tests are commonly employed to assess DES-based formulations.

1. Solubility Studies (Shake-Flask Method)

To determine the equilibrium solubility of the drug in various DES formulations compared with pure water or conventional solvents.

Method:

The shake-flask method involves adding an excess amount of drug to a known volume of DES, followed by shaking at a controlled temperature (typically 25–37 °C) until equilibrium is reached. After centrifugation and filtration, the supernatant is analysed using UV–Vis spectrophotometry or HPLC to quantify dissolved drug concentration.

This method focuses on the extent of solubility enhancement (fold increase), the compatibility between drug and DES components and Hydrogen-bonding or ionic interactions that increase drug solvation. (61,62)

2. Dissolution Studies (USP Type II Paddle Apparatus)

To evaluate the in vitro drug release profile from DES formulations compared with pure drug or other delivery systems.

Method:

The dissolution study is performed using a USP Type II apparatus (paddle method) at 37 ± 0.5 °C, in an appropriate dissolution medium (e.g., phosphate buffer pH 7.4 or 0.1 N HCl). Aliquots are withdrawn at predetermined intervals and analysed spectrophotometrically.

This method focuses on the rate and extent of drug dissolution enhancement, the influence of DES composition and viscosity on dissolution kinetics and the possible reduction in drug crystallinity leading to faster release. (63,64)

3. Characterisation Studies

Analytical characterisation techniques are essential to confirm drug–DES interactions, structural modifications, and changes in crystallinity.

a. Fourier Transform Infrared Spectroscopy (FTIR)

Detects chemical interactions between the drug and DES components via shifts or disappearance of characteristic functional-group peaks.

It involves the Formation of hydrogen bonds or ionic interactions between the drug and DES, confirming molecular compatibility. (65,66)

b. Differential Scanning Calorimetry (DSC)

Measures thermal transitions to assess changes in melting point, glass transition, or crystallinity. Reduction or disappearance of the drug’s melting endotherm indicates amorphisation or eutectic formation. (67)

c. Powder X-Ray Diffraction (PXRD)

Identifies crystalline versus amorphous nature of the drug. A decrease or loss of sharp peaks indicates conversion from crystalline to amorphous state, leading to improved solubility. (68)

d. Scanning Electron Microscopy (SEM)

Examines surface morphology and particle size distribution. Changes from well-defined crystals to irregular or smooth amorphous particles indicate successful incorporation of drug into the DES matrix. (69)

4. Stability Studies

To assess the physical and chemical stability of the DES–drug system under accelerated and ambient storage conditions.

Method:

Formulations are stored at controlled temperatures (25 °C / 60 % RH and 40 °C / 75 % RH) for several weeks or months and periodically tested for drug content, pH, viscosity, and visual changes. (70)

5. Permeability or Diffusion Studies

To evaluate the effect of DES on drug permeation through biological or artificial membranes, simulating absorption behaviour.

Method:

Performed using Franz diffusion cells or Caco-2 cell monolayers. Drug permeation flux and permeability coefficients are calculated. (71)

CONCLUSION

Deep Eutectic Systems (DES) have shown great promise as new ways to improve the dissolution of Cefuroxime Axetil, a BCS Class II medication that doesn't dissolve well in water. The cumulative results from current studies unequivocally demonstrate that DES markedly enhance solubility by modifying the drug's physicochemical characteristics via robust hydrogen-bond interactions, reduced crystallinity, the creation of molecular complexes, and enhanced wettability. These changes in structure and microenvironment make dissolution happen faster and more efficiently than classic methods like solid dispersions or surfactants. Moreover, DES offer notable advantages including simplicity of preparation, low cost, high tunability, and environmental friendliness, aligning them with the principles of green chemistry. Their ability to dissolve a wide spectrum of hydrophobic pharmaceuticals without the use of harmful organic solvents makes them even more important in the pharmaceutical world. The research examined demonstrate that DES can be customized to attain particular release profiles, rendering them suitable for diverse drug delivery needs. However, despite encouraging in vitro results, the translation of DES-based formulations into practical pharmaceutical products requires further exploration. Critical aspects such as long-term physical and chemical stability, regulatory acceptance, toxicological safety, and large-scale manufacturing feasibility remain insufficiently addressed. Furthermore, extensive in vivo pharmacokinetic and pharmacodynamic investigations are necessary to validate the improved bioavailability indicated by in vitro results. In general, DES is a promising, long-lasting, and effective way to make Cefuroxime Axetil and other drugs that don't dissolve well more soluble and easier to dissolve. To fully realize the potential of DES technology and move it closer to clinical and industrial use in modern drug delivery systems, more research that combines formulation optimization, mechanistic studies, and preclinical evaluation is needed.

REFERENCES

1. Kalantri S, Vora A. Eutectic solutions for healing: a comprehensive review on therapeutic deep eutectic solvents (TheDES). Drug Dev Ind Pharm. 2024 May;50(5):387-400. doi: 10.1080/03639045.2024.2345131. Epub 2024 Apr 24. PMID: 38634708.
2. Rautio, J., Kumpulainen, H., Heimbach, T., Oliyai, R., Oh, D., Järvinen, T., & Savolainen, J. (2008). Prodrugs: Design and clinical applications. Nature Reviews Drug Discovery, 7(3), 255–270.
3. Neu, H. C. (1986). Cefuroxime Axetil: An oral cephalosporin. Antimicrobial Agents and Chemotherapy, 30(3), 406–409.
4. Mignini, F., Streccioni, V., & Caputi, A. (2020). Pharmacological and pharmaceutical overview of Cefuroxime Axetil. Journal of Antibiotics Research, 12(2), 45–52.
5. Rautio, J., Kumpulainen, H., Heimbach, T., Oliyai, R., Oh, D., Järvinen, T., & Savolainen, J. (2008). Prodrugs: Design and clinical applications. Nature Reviews Drug Discovery, 7(3), 255–270.
6. Savjani, K. T., Gajjar, A. K., & Savjani, J. K. (2012). Drug solubility: Importance and enhancement techniques. ISRN Pharmaceutics, 2012, 195727.
7. Abbott, A. P., Capper, G., Davies, D. L., Rasheed, R. K., & Tambyrajah, V. (2017). Deep eutectic solvents formed between choline chloride and carboxylic acids: Versatile alternatives to ionic liquids. Journal of the American Chemical Society, 131(6), 2102–2107.
8. Hussain, T., Shakeel, F., & Khar, R. K. (2021). Cefuroxime Axetil: Pharmacokinetic and formulation perspectives for oral bioavailability enhancement. Pharmaceutical Development and Technology, 26(3), 300–312.
9. Savjani, K. T., Gajjar, A. K., & Savjani, J. K. (2012). Drug solubility: Importance and enhancement techniques. ISRN Pharmaceutics, 2012, 195727.
10. Rautio, J., Kumpulainen, H., Heimbach, T., Oliyai, R., Oh, D., Järvinen, T., & Savolainen, J. (2008). Prodrugs: Design and clinical applications. Nature Reviews Drug Discovery, 7(3), 255–270.
11. Patil, V., Sawant, S., & Rathod, V. (2016). Stability studies of Cefuroxime Axetil and approaches for enhancement of its solubility. International Journal of Pharmacy and Pharmaceutical Sciences, 8(11), 101–107.
12. Kumar, S., Singh, S., & Jain, A. (2018). Formulation development and evaluation of Cefuroxime Axetil solid dispersions. Asian Journal of Pharmaceutics, 12(3), S923–S930.
13. Dixit, R., & Patel, P. M. (2017). Physicochemical characterization and formulation aspects of Cefuroxime Axetil. International Journal of Pharmaceutical Sciences Review and Research, 46(1), 89–94.
14. Hussain, T., Shakeel, F., & Khar, R. K. (2021). Cefuroxime Axetil: Pharmacokinetic and formulation perspectives for oral bioavailability enhancement. Pharmaceutical Development and Technology, 26(3), 300–312.
15. Rautio, J., Kumpulainen, H., Heimbach, T., Oliyai, R., Oh, D., Järvinen, T., & Savolainen, J. (2008). Prodrugs: Design and clinical applications. Nature Reviews Drug Discovery, 7(3), 255–270.
16. Mignini, F., Streccioni, V., & Caputi, A. (2020). Pharmacological and pharmaceutical overview of Cefuroxime Axetil. Journal of Antibiotics Research, 12(2), 45–52.
17. Abbott, A. P., Capper, G., Davies, D. L., Rasheed, R. K., & Tambyrajah, V. (2017). Deep eutectic solvents formed between choline chloride and carboxylic acids: Versatile alternatives to ionic liquids. Journal of the American Chemical Society, 131(6), 2102–2107.
18. Amidon, G. L., Lennernäs, H., Shah, V. P., & Crison, J. R. (1995). A theoretical basis for a biopharmaceutic drug classification: The correlation of in vitro drug product dissolution and in vivo bioavailability. Pharmaceutical Research, 12(3), 413–420.
19. Dressman, J. B., Amidon, G. L., Reppas, C., & Shah, V. P. (2001). Dissolution testing as a prognostic tool for oral drug absorption: Immediate release dosage forms. Pharmaceutical Research, 15(1), 11–22.
20. Savjani, K. T., Gajjar, A. K., & Savjani, J. K. (2012). Drug solubility: Importance and enhancement techniques. ISRN Pharmaceutics, 2012, 195727.
21. Vippagunta, S. R., Maul, K. A., Tallavajhala, S., & Grant, D. J. W. (2002). Solid-state characterization of nifedipine solid dispersions. International Journal of Pharmaceutics, 236(1-2), 111–123.
22. Di, L., Fish, P. V., & Mano, T. (2012). Bridging solubility between drug discovery and development. Drug Discovery Today, 17(9-10), 486–495.
23. Jain, A. K., Kesharwani, P., Gupta, U., & Jain, N. K. (2015). A review on solubility enhancement techniques for poorly soluble drugs. International Journal of Pharmaceutical Sciences and Research, 6(7), 2869–2880.
24. Abbott, A. P., Capper, G., Davies, D. L., Rasheed, R. K., & Tambyrajah, V. (2003). Novel solvent properties of choline chloride/urea mixtures. Chemical Communications, (1), 70–71.
25. Smith, E. L., Abbott, A. P., & Ryder, K. S. (2014). Deep eutectic solvents (DESs) and their applications. Chemical Reviews, 114(21), 11060–11082.\
26. Paiva, A., Craveiro, R., Aroso, I., Martins, M., Reis, R. L., & Duarte, A. R. C. (2014). Natural deep eutectic solvents – Solvents for the 21st century. ACS Sustainable Chemistry & Engineering, 2(5), 1063–1071.
27. Dai, Y., van Spronsen, J., Witkamp, G. J., Verpoorte, R., & Choi, Y. H. (2015). Natural deep eutectic solvents as new potential media for green technology. Analytica Chimica Acta, 766, 61–68.
28. Aroso, I. M., Craveiro, R., Rocha, Â., Dionísio, M., Barreiros, S., Reis, R. L., Paiva, A., & Duarte, A. R. C. (2017). Design of controlled release systems for hydrophobic drugs using deep eutectic solvents. European Journal of Pharmaceutics and Biopharmaceutics, 98, 57–66.
29. Shishov, A., Bulatov, A., Locatelli, M., & Andruch, V. (2020). Application of deep eutectic solvents in pharmaceutical and chemical analysis: A review. Microchemical Journal, 154, 104654.
30. Choi, Y. H., van Spronsen, J., Dai, Y., Verberne, M., Hollmann, F., Arends, I. W. C. E., Witkamp, G.-J., & Verpoorte, R. (2011). Are natural deep eutectic solvents the missing link in understanding cellular metabolism and physiology? Plant Physiology, 156(4), 1701–1705.
31. Hussain, T., Shakeel, F., & Khar, R. K. (2021). Cefuroxime Axetil: Pharmacokinetic and formulation perspectives for oral bioavailability enhancement. Pharmaceutical Development and Technology, 26(3), 300–312.
32. Kumar, S., Singh, S., & Jain, A. (2018). Formulation development and evaluation of Cefuroxime Axetil solid dispersions. Asian Journal of Pharmaceutics, 12(3), S923–S930.
33. Vippagunta, S. R., Maul, K. A., Tallavajhala, S., & Grant, D. J. W. (2001). Solid-state characterization of nifedipine solid dispersions. International Journal of Pharmaceutics, 236(1–2), 111–123.
34. Patil, V., Sawant, S., & Rathod, V. (2016). Stability studies of Cefuroxime Axetil and approaches for enhancement of its solubility. International Journal of Pharmacy and Pharmaceutical Sciences, 8(11), 101–107.
35. Savjani, K. T., Gajjar, A. K., & Savjani, J. K. (2012). Drug solubility: Importance and enhancement techniques. ISRN Pharmaceutics, 2012, 195727.
36. Dixit, R., & Patel, P. M. (2017). Physicochemical characterization and formulation aspects of Cefuroxime Axetil. International Journal of Pharmaceutical Sciences Review and Research, 46(1), 89–94.
37. Patil, V., Sawant, S., & Rathod, V. (2016). Stability studies of Cefuroxime Axetil and approaches for enhancement of its solubility. International Journal of Pharmacy and Pharmaceutical Sciences, 8(11), 101–107.
38. Rautio, J., Kumpulainen, H., Heimbach, T., Oliyai, R., Oh, D., Järvinen, T., & Savolainen, J. (2008). Prodrugs: Design and clinical applications. Nature Reviews Drug Discovery, 7(3), 255–270.
39. Kumar, S., Singh, S., & Jain, A. (2018). Formulation development and evaluation of Cefuroxime Axetil solid dispersions. Asian Journal of Pharmaceutics, 12(3), S923–S930.
40. Rautio, J., Kumpulainen, H., Heimbach, T., Oliyai, R., Oh, D., Järvinen, T., & Savolainen, J. (2008). Prodrugs: Design and clinical applications. Nature Reviews Drug Discovery, 7(3), 255–270.
41. Patil, V., Sawant, S., & Rathod, V. (2016). Stability studies of Cefuroxime Axetil and approaches for enhancement of its solubility. International Journal of Pharmacy and Pharmaceutical Sciences, 8(11), 101–107.
42. Dixit, R., & Patel, P. M. (2017). Physicochemical characterization and formulation aspects of Cefuroxime Axetil. International Journal of Pharmaceutical Sciences Review and Research, 46(1), 89–94.
43. Hussain, T., Shakeel, F., & Khar, R. K. (2021). Cefuroxime Axetil: Pharmacokinetic and formulation perspectives for oral bioavailability enhancement. Pharmaceutical Development and Technology, 26(3), 300–312.
44. Savjani, K. T., Gajjar, A. K., & Savjani, J. K. (2012). Drug solubility: Importance and enhancement techniques. ISRN Pharmaceutics, 2012, 195727.
45. Amidon, G. L., Lennernäs, H., Shah, V. P., & Crison, J. R. (1995). A theoretical basis for a biopharmaceutic drug classification: The correlation of in vitro drug product dissolution and in vivo bioavailability. Pharmaceutical Research, 12(3), 413–420.
46. Kumar, P., Singh, S., & Singh, R. (2018). Formulation and evaluation of solid dispersions of Cefuroxime Axetil for dissolution enhancement. Journal of Drug Delivery and Therapeutics, 8(4), 130–137.
47. Rajewski, R. A., & Stella, V. J. (1996). Pharmaceutical applications of cyclodextrins. 2. In vivo drug delivery. Journal of Pharmaceutical Sciences, 85(11), 1142–1169.
48. Patel, A. R., Shah, M., & Dave, R. H. (2020). Cyclodextrin inclusion complexes of Cefuroxime Axetil: Preparation, characterisation, and dissolution enhancement. Drug Development and Industrial Pharmacy, 46(6), 883–890.
49. Khedekar, P. B., & Mittal, S. (2019). Lipid-based delivery systems for poorly water-soluble drugs: A review. European Journal of Pharmaceutical Sciences, 135, 60–72.
50. Patel, V., Desai, T., & Shah, D. (2015). Formulation and evaluation of nanosuspension of Cefuroxime Axetil for solubility enhancement. International Journal of Pharmaceutical Sciences and Research, 6(8), 3434–3440.
51. Abbott, A. P., Capper, G., Davies, D. L., Rasheed, R. K., & Tambyrajah, V. (2003). Novel solvent properties of choline chloride/urea mixtures. Chemical Communications, (1), 70–71.
52. Abbott, A. P., Capper, G., Davies, D. L., Rasheed, R. K., & Tambyrajah, V. (2003). Novel solvent properties of choline chloride/urea mixtures. Chemical Communications, (1), 70–71. https://doi.org/10.1039/B210714G
53. Paiva, A., Craveiro, R., Aroso, I., Martins, M., Reis, R. L., & Duarte, A. R. C. (2014). Natural deep eutectic solvents – Solvents for the 21st century. ACS Sustainable Chemistry & Engineering, 2(5), 1063–1071. https://doi.org/10.1021/sc500096j
54. Aroso, I. M., Craveiro, R., Rocha, Â., Dionísio, M., Barreiros, S., Reis, R. L., & Duarte, A. R. C. (2015). Design of therapeutic deep eutectic solvents for drug solubilization and delivery. Chemical Communications, 51(26), 5344–5347. https://doi.org/10.1039/C4CC09526F
55. Sánchez-Fernández, A., P?otka-Wasylka, J., & Kalembkiewicz, J. (2021). Therapeutic deep eutectic solvents (THEDES): An emerging platform for pharmaceutical drug delivery. Molecules, 26(3), 620. https://doi.org/10.3390/molecules26030620
56. Nica, M.-A., Anu?a, V., Nicolae, C. A., Popa, L., Ghica, M. V., Coco?, F.-I., & Dinu-Pîrvu, C.-E. (2024). Exploring Deep Eutectic Solvents as Pharmaceutical Excipients: Enhancing the Solubility of Ibuprofen and Mefenamic Acid. Pharmaceuticals, 17(10), 1316. https://doi.org/10.3390/ph17101316
57. Ijardar, S. P., Singh, V., & Gardas, R. L. (2022). Revisiting the Physicochemical Properties and Applications of Deep Eutectic Solvents. Molecules, 27(4), 1368. https://doi.org/10.3390/molecules27041368
58. Shumilin, I., Tanbuz, A., & Harries, D. (2023). Deep Eutectic Solvents for Efficient Drug Solvation: Optimizing Composition and Ratio for Solubility of β-Cyclodextrin. Pharmaceutics, 15(5), 1462. https://doi.org/10.3390/pharmaceutics15051462
59. Ijardar, S. P., Singh, V., & Gardas, R. L. (2022). Revisiting the Physicochemical Properties and Applications of Deep Eutectic Solvents. Molecules, 27(4), 1368. https://doi.org/10.3390/molecules27041368
60. Chakraborty, S., Sathe, R. Y., Chormale, J. H., Dangi, A., Bharatam, P. V., & Bansal, A. K. (2023). Effect of Deep Eutectic System (DES) on Oral Bioavailability of Celecoxib: In Silico, In Vitro, and In Vivo Study. Pharmaceutics, 15(9), 2351. https://doi.org/10.3390/pharmaceutics15092351
61. Dangre et al. (2023) reported significant solubility improvement for poorly soluble drugs in tailored DES formulations using this method.
62. Dangre, P. V., et al. (2023). Tailoring deep eutectic solvents to provoke solubility and dissolution. ACS Omega, 8(6), 5431–5440. https://doi.org/10.1021/acsomega.2c08031
63. Aroso et al. (2016) demonstrated increased dissolution rates for ibuprofen formulated in THEDES compared with its crystalline form.
64. Aroso, I. M., et al. (2016). Dissolution enhancement of active pharmaceutical ingredients by therapeutic deep eutectic systems. European Journal of Pharmaceutics and Biopharmaceutics, 98, 57–66.
65. Shishov et al. (2017) reported FTIR shifts in ibuprofen–choline chloride DES, indicating strong hydrogen bonding.
66.  Shishov, A., et al. (2017). Application of deep eutectic solvents for pharmaceutical analysis. TrAC Trends in Analytical Chemistry, 97, 156–168.
67. Cysewski, P., et al. (2024). Experimental and ML-assisted design of DES for NSAID solubility. Journal of Molecular Liquids.
68. Hayyan, M., Hashim, M. A., & Hayyan, A. (2015). Investigating the solubility of antifungal drugs in deep eutectic solvents. Journal of Molecular Liquids, 208, 255–263.
69. Lomba, L., et al. (2023). Ibuprofen solubility and cytotoxic study in sugar-based DES. Journal of Molecular Liquids, 384, 122342.
70. Oliveira, F., et al. (2021). Therapeutic deep eutectic systems for pharmaceutical applications. Current Pharmaceutical Design, 27(30), 3984–3996.*
71. Aroso et al. (2016) observed enhanced permeation of ibuprofen from THEDES due to increased thermodynamic activity of the solubilised drug.