A microemulsion system based on natural eutectic solvent, methotrexate self-microemulsifying drug delivery system and application

Abstract

The application discloses a kind of microemulsion systems based on natural eutectic solvent, methotrexate (MTX) self-microemulsifying drug delivery system and application, belong to medical technology field.The application is prepared two kinds of natural eutectic solvent microemulsion systems by COSMO screening: ethylene glycol-oxalic acid microemulsion (EG-OA-ME) and ethylene glycol-malonate microemulsion (EG-PA-ME), and the drug loading of MTX in the optimized EG-OA-ME and EG-PA-ME is 40.00mg / g and 4.00mg / g respectively, which is significantly higher than the solubility of MTX in water.In addition, MTX is more stable in EG-PA-ME, the permeability of drug-loaded EG-PA-ME is high, and the cytotoxicity is small.The application not only significantly improves the solubility and transdermal effect of MTX, but also effectively saves the cost, and has potential application prospect in the treatment of various inflammatory and tumor diseases.

Description

Technical Field

[0001] This invention relates to the field of pharmaceutical technology, and in particular to a microemulsion system based on a natural eutectic solvent, a methotrexate self-microemulsion drug delivery system, and its applications. Background Technology

[0002] Methotrexate (MTX) is an effective folic acid antagonist that can be used to treat various inflammatory and neoplastic diseases, including skin cancer, psoriasis, and rheumatoid arthritis.

[0003] Methotrexate has the chemical formula C 20 H 22 N8O5, with a molecular weight of 454.493, is an orange-yellow crystalline powder with poor water and lipid solubility, and is almost insoluble in water, ethanol, chloroform, and ether. Currently, the main dosage forms for methotrexate are tablets and injections. However, long-term, high-dose administration often causes systemic complications, easily leading to side effects such as femoral head necrosis, hypertension, and weight gain. Injectable formulations require specialized operation and frequent administration to maintain effective blood drug concentrations. New methods are urgently needed to improve these methods, reduce side effects, enhance patient compliance, and optimize treatment efficacy. For example, developing sustained-release formulations, transdermal drug delivery systems, or targeted delivery technologies could reduce dosing frequency, decrease systemic exposure, and improve local drug efficacy. Currently, transdermal MTX drug delivery systems mainly include liposomes, hydrogels, nanoparticles, and nanoemulsions, which have improved transdermal efficiency and bioavailability to some extent, but still have limitations such as limited drug loading capacity, poor stability, complex preparation processes, or insufficient transdermal effects. Therefore, there is an urgent need to develop a high-efficiency, stable, biocompatible, and easily mass-producible sustained-release drug delivery system.

[0004] Natural eutectic solvents (NADES) are composed of natural primary metabolites such as amino acids, organic acids, sugars, choline derivatives, or urea. They are green solvents formed by hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs) linked together by hydrogen bonds. They offer advantages such as flexible design, low cost-effectiveness, biodegradability, and good biocompatibility, and can significantly improve drug solubility and skin permeability. In pharmaceutical science, microemulsions based on NADES have become an effective nanocarrier, especially suitable for drugs with poor water solubility or instability. There is considerable interest in the application of this technology in drug delivery. Currently, there are no reports on using NADES to address the low solubility of MTX drugs and the skin barrier effect during transdermal delivery. Summary of the Invention

[0005] The purpose of this invention is to provide a microemulsion system based on a natural eutectic solvent, a methotrexate self-microemulsion drug delivery system, and its application, in order to solve the problems existing in the prior art. The microemulsion system based on a natural eutectic solvent constructed by this invention is not only simple and green in preparation process and has low cytotoxicity, but also greatly improves drug loading and skin permeability. It is a good drug sustained-release system, providing a scientific basis for solving problems such as low solubility of MTX drugs and skin barrier effects in transdermal delivery.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] This invention provides a microemulsion system based on a natural eutectic solvent. The microemulsion system includes a natural eutectic solvent and an emulsifier. The natural eutectic solvent is a mixture of ethylene glycol and any one of oxalic acid and malonic acid in an equimolar ratio. The emulsifier is a mixture of a transdermal penetration enhancer and a surfactant.

[0008] Preferably, the mass ratio of the transdermal penetration enhancer to the surfactant is (1:9)-(9:1);

[0009] And / or the transdermal penetration enhancer is isopropyl myristate;

[0010] And / or the surfactant is composed of Tween 80 and Span 20 in a mass ratio of (1:2) to (2:1).

[0011] Preferably, in the emulsifier, the mass ratio of isopropyl myristate to the surfactant is 7:3; and / or in the ethylene glycol-oxalic acid microemulsion system formed by ethylene glycol, oxalic acid, and the emulsifier, the mass ratio of Tween 80 to Span 20 is 1:2; and in the ethylene glycol-malonic acid microemulsion system formed by ethylene glycol, malonic acid, and the emulsifier, the mass ratio of Tween 80 to Span 20 is 1:1.

[0012] Preferably, when the natural eutectic solvent is ethylene glycol and oxalic acid, the mass ratio of the natural eutectic solvent to the emulsifier is 0.12:1; when the natural eutectic solvent is ethylene glycol and malonic acid, the mass ratio of the natural eutectic solvent to the emulsifier is 0.1:1.

[0013] This invention also provides a method for preparing the microemulsion system based on a natural eutectic solvent, comprising the following steps:

[0014] According to the required proportions of each raw material in the system, ethylene glycol is mixed with any one of oxalic acid and malonic acid in an equimolar ratio, and heated and stirred at a water bath temperature of 100°C until a clear and transparent solution is obtained, thus preparing a natural eutectic solvent.

[0015] A transdermal penetration enhancer and a surfactant are mixed to prepare an emulsifier; then, the natural eutectic solvent is added to the emulsifier and stirred to obtain the microemulsion system based on the natural eutectic solvent.

[0016] The present invention also provides a methotrexate self-microemulsion drug delivery system, which includes methotrexate and the microemulsion system.

[0017] Preferably, when the natural eutectic solvent is ethylene glycol and oxalic acid, the drug loading of the methotrexate self-microemulsion drug delivery system is 40.00 mg / g; when the natural eutectic solvent is ethylene glycol and malonic acid, the drug loading of the methotrexate self-microemulsion drug delivery system is 4.00 mg / g.

[0018] This invention also provides a method for preparing the methotrexate self-microemulsion drug delivery system, wherein MTX is added to a corresponding oil-in-oil natural eutectic solvent microemulsion (NADES / O), and stirred continuously at 25°C for 48 hours to prepare an MTX-loaded ethylene glycol-oxalate drug-loaded microemulsion (MTX-EG-OA-ME) and an ethylene glycol-malonic acid drug-loaded microemulsion (MTX-EG-PA-ME), which is the methotrexate self-microemulsion drug delivery system.

[0019] This invention also provides the application of the microemulsion system in any of the following:

[0020] (1) Application in the preparation of methotrexate delivery carriers;

[0021] (2) Application in improving the solubility of methotrexate;

[0022] (3) Application in the preparation of pharmaceutical formulations that enhance the permeability of methotrexate in the skin.

[0023] The present invention discloses the following technical effects:

[0024] (1) In this invention, the raw material used is NADES, which is derived from nature, has low preparation cost, is biodegradable, and is more in line with the principles of green chemistry.

[0025] (2) In this invention, the EG-PA-ME selected has very low cytotoxicity.

[0026] (3) In this invention, the drug loading of MTX in the screened EG-PA-ME is 4.00 mg / g, which greatly improves the drug solubility.

[0027] (4) In this invention, the permeability of MTX in the screened EG-PA-ME is three times that of 0.01M phosphate buffered saline with a pH of 7.4, which greatly improves the bioavailability of MTX.

[0028] (5) In this invention, the particle size of MTX-EG-PA-ME remains stable at 4℃, 25℃ and 40℃, and its particle size and PDI remain relatively unchanged within one month. This indicates that EG-PA-ME has excellent stability and is expected to be used for drug delivery. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 The following are the results of solubility calculations using the real solvent-like conductor shielding model (COSMO-RS), σ distribution maps of the compounds, and calculation results of the interaction energy between MTX and different NADES: (a): Predicted solubility of MTX in 870 NADES; (b)-(c): σ distribution maps of MTX with different NADES; (d): Interaction energy between MTX and different NADES.

[0031] Figure 2 (a) Solubility of MTX in NADES; (b) Solubility of MTX in 16 NADESs screened by COSMO-RS and its solubilizing factor in water; (c) Solubilizing ability of 5 NADESs with high solubility for MTX at different molar ratios; (d) Effect of water content on solubility of the two NADESs finally screened (EG-OA and EG-PA).

[0032] Figure 3 The pseudo-ternary phase diagram of EG-OA-ME microemulsion;

[0033] Figure 4 The pseudo-ternary phase diagram of EG-PA-ME microemulsion;

[0034] Figure 5 The particle size distribution of microemulsions containing transdermal facilitators and surfactants in three mass ratios and clear photographs of microemulsions with a mass ratio of 7:3; (a): EG-OA-ME, (b): EG-PA-ME;

[0035] Figure 6The properties of two drug-loaded NADES / O microemulsions are shown below: (a) Schematic diagram of the solubility of MTX in the two NADES / O microemulsions; (b) Particle size of MTX-EG-PA-ME at 4℃, 25℃ and 40℃; (c) Particle size of MTX-EG-OA-ME at 4℃, 25℃ and 40℃; (d) Changes in particle size and PDI of MTX-EG-PA-ME after one month of storage at 25℃.

[0036] Figure 7 This is a schematic diagram showing the cumulative percentage of MTX penetration through mouse skin via three delivery systems: phosphate-buffered saline (PBS), ethylene glycol-malonic acid (EG-PA), and EG-PA-ME.

[0037] Figure 8 Cell viability of HaCaT cells after treatment with different systems;

[0038] Figure 9 This is a schematic diagram illustrating the implementation principle of the present invention, which uses a microemulsion system loaded with MTX based on a natural eutectic solvent. Detailed Implementation

[0039] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0040] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0041] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0042] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0043] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0044] This invention constructs a microemulsion system based on a natural eutectic solvent and loads MTX onto it. A schematic diagram of the implementation principle is shown below. Figure 9 As shown in the figure, the construction and application process of the microemulsion system based on a natural eutectic solvent and the methotrexate self-microemulsion drug delivery system are clearly illustrated.

[0045] Example 1: COSMO-RS screening for NADES

[0046] This invention uses COSMO-RS to screen 16 NADES species from 870 species to identify those with good solubility for MTX. The results are as follows: Figure 1 As shown, by Figure 1 As shown in section a, NADES formed when HBA is a polyol and HBD is an organic acid exhibits good drug-dissolving ability. Furthermore, NADES formed when HBA is an organic base and a quaternary ammonium salt, along with polyols and a few amino acids, also demonstrate good drug-dissolving ability. However, NADES formed when HBA is an organic amine and an amino acid exhibit relatively weak drug-dissolving ability. Figure 1 As shown in points b and c, NADES composed of polyols and organic acids exhibits strong solubilizing properties for MTX. Subsequent experiments will use polyols and organic acids to prepare NADES. Figure 1 As can be seen from d, hydrogen bonding is the main factor promoting the solubility of MTX.

[0047] Example 2: Preparation of NADES

[0048] Table 1 lists the specific compositions of 16 highly soluble NADES compounds. The components were mixed in equimolar amounts in a 100 mL round-bottom flask and heated in a water bath at 100°C using a magnetic stirrer until a clear, transparent solution of each of the 16 NADES compounds was obtained.

[0049] Table 1. Composition and related information of the 16 types of NADES prepared.

[0050]

[0051] Example 3: Solubility experiment of MTX in 16 NADES

[0052] Add 1 g of NADES and a certain amount of MTX to a 2 mL centrifuge tube. Vortex the mixture for 5 min to ensure complete dispersion and dissolution, then sonicate at room temperature for 20 min (SY-500MD, China) to promote complete dissolution. Centrifuge the sample at 10,000 rpm for 1 min, and filter the resulting supernatant through a 0.22 μm organic membrane. The solubility was then quantified by HPLC. Table 2 shows the HPLC detection method.

[0053] Table 2 HPLC Detection Methods

[0054]

[0055]

[0056] Solubility results as follows Figure 2 As shown, by Figure 2 As shown in section a, compared to the solubility of MTX in water (0.12 mg / g), its solubility in NADES increased by approximately 43-864 times. Figure 2 As shown in section b, among the five NADES compounds with high solubility, the solubilization efficiency of MTX gradually decreased with increasing proportion of organic acids in the NADES. Specifically, EG-OA and EG-PA (with HBD and HBA ratios of 1:1) exhibited the highest solubility, at 103.63 mg / g and 81.12 mg / g, respectively, representing increases of 864 times and 676 times compared to their solubility in water. Therefore, they were selected for further evaluation. Figure 2 As shown in c, the solubilization efficiency of MTX in both types of NADES decreases with increasing water content. This phenomenon is attributed to the fact that water disrupts the low eutectic hydrogen bond structure, thereby reducing its solubilization ability.

[0057] Example 4: Determination of Two NADES / O Microemulsion Systems

[0058] In current patent literature and academic research, mass ratio is widely used as an important parameter in the preparation of microemulsions. Therefore, this invention also prioritizes using mass ratio as a reference in its experimental design to maintain consistency and comparability with existing research, providing more reliable support for subsequent experimental results analysis and theoretical discussions.

[0059] 1. Determination of the mass ratio of Tween 80 and Span 20

[0060] Under constant temperature conditions of 25°C, the optimal composition was determined by varying the ratio of isopropyl myristate (IPM), Tween 80 (surfactant, T), and Span 20 (auxiliary surfactant, S). The mass ratio of Tween 80 to Span 20 was systematically adjusted to 2:1, 3:2, 1:1, 2:3, and 1:2. At specific surfactant ratios, the mass ratio of IPM to the mixed surfactants varied between 1:9 and 9:1. NADES was gradually added to the IPM / Tween 80 / Span 20 mixture under continuous, moderate magnetic stirring until the mixture changed from turbid to clear and then back to turbid. The mass of NADES added was carefully recorded, a pseudo-ternary phase diagram was plotted, and the optimal ratio was determined.

[0061] The results are as follows Figure 3 and Figure 4 As shown, the microemulsion regions of both NADES / O systems are larger than those of W / O. Table 3 shows that EG-OA-ME has the largest microemulsion area when the T / S mass ratio is 1:2, and EG-PA-ME has the largest microemulsion area when the T / S mass ratio is 1:1. These ratios indicate optimal stability and are therefore selected for further evaluation.

[0062] Table 3 Microemulsion area under different T / S ratios

[0063]

[0064]

[0065] 2. Determination of the mass ratio of IPM to mixed surfactants

[0066] Since a higher oil content facilitates transdermal absorption, a lower surfactant content results in lower cytotoxicity, and a microemulsion with a mass ratio of 9:1 is not easily formed, dynamic light scattering (DLS) measurements were performed using IPM and mixed surfactant mass ratios of 6:4, 7:3, and 8:2 to determine the appropriate ratio.

[0067] Depend on Figure 5 It was found that microemulsions with mass ratios of 8:2 and 7:3 exhibited more uniform particle size distribution, which may be more beneficial to the stability of the system. Meanwhile, particle size measurements (Table 4) showed that decreasing the oil phase ratio and increasing the surfactant phase increased the microemulsion particle size, due to the increased NADES content in the system. Although the increased NADES content leads to larger particle size, it also improves drug solubility. Considering all factors, for both EG-OA-ME and EG-PA-ME microemulsion systems, a mass ratio of IPM to mixed surfactant of 7:3 was selected for further investigation.

[0068] Table 4. Particle size and PDI at different IPM and T+S ratios

[0069]

[0070] 3. Preparation of two NADES / O microemulsion systems

[0071] Based on the determined mass ratios of Tween80 and Span20, and IPM and mixed surfactants, two NADES / O microemulsion systems were prepared. Specific preparation ratios are detailed in Table 5.

[0072] Table 5. Mass ratio of the two NADES / O microemulsion systems

[0073] EG-OA-ME 2.4 14 2 4 EG-PA-ME 2.0 14 3 3

[0074] 4. Determination of Microemulsion Type

[0075] In addition, the diffusion rates of the red oil-soluble dye (Sudan Red III) and the blue water-soluble dye (methylene blue) were measured to classify the microemulsion type. The experiment found that the diffusion rate of Sudan Red III was greater than that of methylene blue, indicating that the formed microemulsion was of the water-in-oil (W / O) type.

[0076] Example 5: Drug loading performance of two NADES / O microemulsions

[0077] 1. Solubility of MTX in two NADES / O microemulsions

[0078] Excess MTX was added to the corresponding NADES / O microemulsion, and the mixture was stirred continuously at 25°C for 48 hours. Undissolved MTX was then removed using a 0.22 μm filter membrane. The solubility of MTX in these formulations was quantified using HPLC.

[0079] The results are as follows Figure 6 As shown in Figure a, the results indicate that the solubility of MTX in EG-OA-ME was 43.60 mg / g, and in EG-PA-ME it was 6.59 mg / g, which were 363.33 times and 54.92 times higher in water, respectively. Both NADES / O microemulsions significantly increased the drug loading of MTX and substantially improved its bioavailability.

[0080] 2. Preparation of two drug-loaded NADES / O microemulsions

[0081] Excessive drug loading in the microemulsion system during the experiment could lead to instability. Therefore, the drug loading amounts chosen for preparing the two drug-loaded NADES / O microemulsions were 40 mg / g and 4 mg / g, respectively. By adding a certain amount of MTX to the corresponding NADES / O microemulsion and stirring continuously at 25°C for 48 hours, MTX-loaded microemulsions MTX-EG-OA-ME (40 mg / g) and MTX-EG-PA-ME (4 mg / g) were prepared. Specific preparation ratios are shown in Table 6.

[0082] Table 6. Mass ratio of two drug-loaded NADES / O microemulsions

[0083] MTX-EG-OA-ME 896 2.4 14 2 4 MTX-EG-PA-ME 88 2.0 14 3 3

[0084] 3. Stability of drug-loaded NADES / O microemulsion

[0085] The particle size of two drug-loaded NADES / O microemulsions at different temperatures and the particle size change of MTX-EG-PA-ME over one month were determined using DLS.

[0086] The results are as follows Figure 6 As shown in Figures b and c, the particle size of MTX-EG-PA-ME remained stable at 4°C, 25°C, and 40°C. For MTX-EG-OA-ME, no significant particle size change was observed at 4°C and 25°C, while a slight increase was observed at 40°C, which may be due to droplet aggregation at high temperatures. Furthermore, [the text abruptly ends here, likely due to an incomplete sentence or missing information]. Figure 6 As shown in Figure d, the particle size and polydispersity index (PDI) of MTX-EG-PA-ME remained relatively unchanged over a month, indicating its excellent stability and promising potential for drug delivery.

[0087] Example 6 Skin Permeability Assessment

[0088] Mouse skin was fixed between the donor and recipient chambers of a Franz diffusion cell, with the stratum corneum facing the donor chamber. 0.01M PBS at pH 7.4 was injected into the recipient chamber. The water bath temperature was maintained at a stable 37±0.3℃, and the magnetic stirring speed was set to 300 rpm to promote diffusion. EG-PA and EG-PA-ME containing the drugs were uniformly applied to the skin surface. At regular intervals, 0.2 mL samples were collected from the recipient solution and immediately replaced with fresh PBS to maintain a constant volume.

[0089] The cumulative drug penetration rate is calculated using HPLC data according to the following formula.

[0090]

[0091] Among them, Q n= Cumulative percentage of drug penetration; C n = Drug concentration in the receptor fluid at the nth sampling interval; V = Volume of the receptor cell chamber (11 mL); C i = Drug concentration in the receptor fluid at the (n-1)th sampling; V i = Sample volume (0.2 mL); A = Initial total drug amount (1 mg / g).

[0092] Depend on Figure 7 It was observed that after 48 hours, the cumulative permeability of the drug-loaded phosphate-buffered saline (MTX-PBS) solution was only 7.75%, while the cumulative permeability of the drug-loaded ethylene glycol-malonic acid eutectic solvent (MTX-EG-PA) solution reached 18.80%, and the cumulative permeability of the MTX-EG-PA-ME solution was 23.87%. These results indicate that the EG-PA formulation has superior permeability, which is attributed to the presence of ethylene glycol, a known permeability enhancer. Furthermore, the excellent permeability factor IPM (another well-known permeability enhancer) in the EG-PA-ME group was enhanced by the co-presentation of NADES. These observations confirm that the EG-PA-ME developed in this invention can significantly improve the skin permeability of MTX, thereby improving absorption and bioavailability.

[0093] Example 7

[0094] HaCaT cells were seeded into 96-well plates and cultured at 37°C and 5% CO2 for 24 hours. After culturing, the cells were washed with PBS, and then an equal volume of NADES or microemulsion was added, followed by incubation at 37°C for another 24 hours. CCK-8 solution was then added, and the cells were cultured for another 4 hours. The absorbance at 450 nm was measured using a BioTek Gen5 microplate reader, and cell viability was determined according to the formula.

[0095]

[0096] Among them, A test and A control A represents the absorbance of the treated cells and the control cells, respectively. blank This represents the absorbance of cells-free pores.

[0097] The results are as follows Figure 8 As shown, compared with the control group, the cell survival rate of both NADES / O microemulsions exceeded 90%, indicating that they have low cytotoxicity as drug carriers.

[0098] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A microemulsion system based on a natural eutectic solvent, characterized in that, The microemulsion system comprises a natural eutectic solvent and an emulsifier. The natural eutectic solvent is a mixture of ethylene glycol and any one of oxalic acid and malonic acid in an equimolar ratio. The emulsifier is a mixture of a transdermal penetration enhancer and a surfactant. The transdermal penetration enhancer is isopropyl myristate; The surfactant is composed of Tween 80 and Span 20 in a mass ratio of (1:2) to (2:1); In the emulsifier, the mass ratio of isopropyl myristate to the surfactant is 7:3; in the ethylene glycol-oxalic acid microemulsion system formed by ethylene glycol, oxalic acid, and the emulsifier, the mass ratio of Tween 80 to Span 20 is 1:2; in the ethylene glycol-malonic acid microemulsion system formed by ethylene glycol, malonic acid, and the emulsifier, the mass ratio of Tween 80 to Span 20 is 1:

1.

2. The microemulsion system based on a natural eutectic solvent as described in claim 1, characterized in that, When the natural eutectic solvent is ethylene glycol and oxalic acid, the mass ratio of the natural eutectic solvent to the emulsifier is 0.12:1; when the natural eutectic solvent is ethylene glycol and malonic acid, the mass ratio of the natural eutectic solvent to the emulsifier is 0.1:

1.

3. A method for preparing a microemulsion system based on a natural eutectic solvent as described in claim 1 or 2, characterized in that, Includes the following steps: According to the required proportions of each raw material in the system, ethylene glycol is mixed with any one of oxalic acid and malonic acid in an equimolar ratio, and heated and stirred at a water bath temperature of 100°C until a clear and transparent solution is obtained, thus preparing a natural eutectic solvent. A transdermal penetration enhancer and a surfactant are mixed to prepare an emulsifier; then, the natural eutectic solvent is added to the emulsifier and stirred to obtain the microemulsion system based on the natural eutectic solvent.

4. A methotrexate self-microemulsion drug delivery system, characterized in that, It includes methotrexate and the microemulsion system based on a natural eutectic solvent as described in claim 1 or 2.

5. The methotrexate self-microemulsion drug delivery system as described in claim 4, characterized in that, When the natural eutectic solvent is ethylene glycol and oxalic acid, the drug loading of the methotrexate self-microemulsion drug delivery system is 40.00 mg / g; when the natural eutectic solvent is ethylene glycol and malonic acid, the drug loading of the methotrexate self-microemulsion drug delivery system is 4.00 mg / g.

6. A method for preparing a methotrexate self-microemulsion drug delivery system as described in claim 4 or 5, characterized in that, By adding MTX to the corresponding oil-in-oil natural eutectic solvent microemulsion and stirring continuously at 25°C for 48 hours, MTX-loaded ethylene glycol-oxalate drug-loaded microemulsions and ethylene glycol-malonic acid drug-loaded microemulsions were prepared, which are the methotrexate self-microemulsion drug delivery systems.

7. The use of the microemulsion system based on a natural eutectic solvent as described in claim 1 or 2 in any of the following: (1) Application in the preparation of methotrexate delivery carriers; (2) Application in the preparation of pharmaceutical formulations that improve the solubility of methotrexate; (3) Application in the preparation of pharmaceutical formulations that improve the permeability of methotrexate in the skin.

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