A method for preparing tacrolimus capsules

Abstract

This invention discloses a method for preparing tacrolimus capsules, relating to the field of pharmaceutical technology. The preparation method includes: S1, preparation of the drug-loaded pellet core; S2, coating and curing with a flexible buffer layer, curing at 100°C and 35% relative humidity for 8 hours to induce xanthan gum swelling; S3, high-barrier coating; S4, protective controlled-release coating, using a coating solution prepared by combining a third polymer grafted with lipophilic bile salt derivatives and phospholipids; S5, capsule filling. This invention, through a functionally graded multilayer structure design and precise control of phospholipid composition and spatial distribution, synergistically solves multiple technical problems related to tacrolimus, such as poor chemical stability, coating brittleness and breakage, drug burst release, dissolution and absorption barriers, and release drift due to individual differences in gastric emptying. It achieves excellent mechanical strength of the microcapsules, stable and controllable release kinetics, and a significant solubilizing effect. The process parameters of this method are clearly defined and suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of pharmaceutical technology, and in particular to a method for preparing tacrolimus capsules. Background Technology

[0002] Tacrolimus, a potent macrolide immunosuppressant, is widely used for treating organ transplant rejection and autoimmune diseases. This compound exhibits significant lipid solubility, extremely low solubility in aqueous media, and is highly sensitive to light, heat, and humidity. It is prone to chemical degradation during formulation and storage, leading to reduced drug potency and altered impurity profiles. Currently, tacrolimus microcapsule formulations are commonly used clinically, employing polymer coating technology to achieve drug stabilization and release regulation. However, this type of formulation presents a significant technical challenge: the high-strength, high-density coating materials used to provide a sufficient environmental barrier often exhibit significant brittleness. Under mechanical stress from transportation vibrations and packaging compression, microcracks or even complete breakage of the coating layer can easily occur, resulting in loss of drug protection and potentially causing burst release in vivo, leading to drastic fluctuations in blood drug concentration and affecting the safety and predictability of efficacy.

[0003] To address the aforementioned issues, existing technologies disclose a solution that involves constructing a xanthan gum-containing coating layer and combining it with a high-temperature, low-humidity curing process to induce a swollen state in the xanthan gum. This solution can improve the density and mechanical toughness of the coating layer. However, this technology primarily addresses the crystallization problem of itraconazole. It still lacks a systematic solution to the multiple complex issues faced by tacrolimus formulations, including dissolution and absorption barriers due to extreme lipid solubility, the inherent brittleness of high-barrier coatings, and release timing drift caused by physiological differences in gastric emptying among patients. Therefore, there is a need to develop a novel tacrolimus microgranule formulation that simultaneously achieves chemical stability, mechanical integrity, controllable release, and absorption-promoting functions. Summary of the Invention

[0004] This application provides a method for preparing tacrolimus capsules, solving the comprehensive technical problem in the prior art where tacrolimus microgranules cannot simultaneously meet the requirements of chemical stability, mechanical strength, release controllability, and absorption promotion, thus achieving multi-dimensional synergistic optimization of formulation performance. This technical solution achieves a unified approach to drug stabilization, dosage form anti-brittleness, programmed release, and absorption promotion through a functionally graded multilayer structure design and precise control.

[0005] This application provides a method for preparing tacrolimus capsules, comprising the following steps: S1. Preparation of drug-loaded pellet cores: Tacrolimus and hydroxypropyl methylcellulose E5 are dissolved in an organic solvent to prepare a coating solution. The pellet cores are coated with the drug using a fluidized bed and then dried to obtain drug-loaded pellet cores. S2, Flexible buffer layer coating and curing: The first polymer is dissolved in water, xanthan gum is added and dispersed evenly, and the drug-loaded pellet core is coated using a fluidized bed. After drying, the pellets are cured for 8 hours at a temperature of 100°C and a relative humidity of 35% to obtain cured pellets. S3, High Barrier Coating: The second polymer is dissolved in an organic solvent, and the matured microcapsules are coated in a fluidized bed to obtain high barrier coated microcapsules. S4. Protective controlled-release coating: A coating solution is prepared by combining a third polymer grafted with lipophilic bile salt derivatives and phospholipids. The high-barrier microspheres are coated using a fluidized bed and then dried to obtain multi-layer coated microspheres. S5. Capsule filling: The obtained multi-layer coated microspheres are filled into capsule shells; The first polymer is hydroxypropyl methylcellulose E50, the second polymer is ethyl cellulose, and the third polymer is polyacrylic acid resin.

[0006] Furthermore, the content of each component, in parts by weight, is as follows: 180 portions of pellet core; 100 doses of tacrolimus; Hydroxypropyl methylcellulose E5 160 parts; 100 parts of the first polymer; 10 parts xanthan gum; 60 parts of the second polymer; 100 parts of the third polymer; Lipophilic bile salt derivatives, 2-10 parts; Phospholipids 5-15 parts.

[0007] Furthermore, the lipophilic bile salt derivative is sodium taurocholate; The phospholipid is at least one of hydrogenated soybean phospholipid, partially hydrogenated soybean phospholipid, or non-hydrogenated soybean phospholipid.

[0008] Furthermore, the preparation of the coating solution for protecting the controlled-release layer in step S4 includes: A1. Preparation of bile salt-polymer copolymer: The third polymer was dissolved in a solvent, activated, and then reacted with a lipophilic bile salt derivative at 38°C for 18 hours. The copolymer powder was purified, dried, and pulverized. A2. Preparation of coating solution: The copolymer powder is mixed with phospholipids and added to a mixed solvent consisting of isopropanol and water in a volume ratio of 9:1. The mixture is then homogenized under a pressure of 1000 bar. A colloidal dispersion with a particle size D90 ≤ 200 nm is obtained, which is the protective controlled-release coating solution.

[0009] Furthermore, the phospholipids are a complex system of phospholipids with different degrees of hydrogenation, including a first hydrogenated phospholipid, a second hydrogenated phospholipid, and a third hydrogenated phospholipid. The first hydrogenated phospholipid has a hydrogenation degree ≥90% and a phase transition temperature of 55℃; The second hydrogenated phospholipid has a hydrogenation degree of 40-60% and a phase transition temperature of 35-45℃; The third hydrogenated phospholipid has a hydrogenation degree of ≤5% and a phase transition temperature of less than 0°C.

[0010] Furthermore, the mass ratio of the first hydrogenated phospholipid, the second hydrogenated phospholipid, and the third hydrogenated phospholipid is as follows: First hydrogenated phospholipid 70%, second hydrogenated phospholipid 25%, third hydrogenated phospholipid 5%; Or, 30% first hydrogenated phospholipid, 50% second hydrogenated phospholipid, and 20% third hydrogenated phospholipid; Or, 10% first hydrogenated phospholipid, 30% second hydrogenated phospholipid, and 60% third hydrogenated phospholipid.

[0011] Furthermore, the protective controlled-release layer described in step S4 includes an inner sublayer and an outer sublayer; The inner sublayer is enriched with first hydrogenated phospholipids, and the outer sublayer is enriched with third hydrogenated phospholipids; In the inner sublayer, the first hydrogenated phospholipid accounts for 80% of the total phospholipids in the inner sublayer, and the second hydrogenated phospholipid accounts for 20%. The third hydrogenated phospholipid accounts for 80% of the total phospholipids in the outer sublayer, and the second hydrogenated phospholipid accounts for 20%; the dry weight ratio of the outer sublayer to the inner sublayer is 9:11.

[0012] Furthermore, in step S4, a double-layer coating process is adopted: first, the inner sublayer is coated, and the coating weight is increased to 55% of the total dry weight of the outer layer, and then dried for 15 minutes; then, the outer sublayer is coated, and the coating weight is increased to 45% of the total dry weight of the outer layer, and then dried for 40 minutes.

[0013] Furthermore, the fluidized bed coating process parameters are as follows: Inlet air temperature 35-42℃, outlet air temperature 30-37℃, atomization pressure 1.2-1.5 bar; The drying temperature in the fluidized bed coating process is 30-40℃, and the drying time is 15-40 minutes.

[0014] Furthermore, the core particle size is 500-600 μm, and the multi-layer coated microspheres have a particle size of 950-1050 μm.

[0015] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages: By employing a synergistic design at the molecular and material levels, the inner layer of cured xanthan gum network ensures the physical integrity of the dosage form and solves the problem of mechanical fragility. The outer layer of bile salt-phospholipid complex system constructs an intelligent response interface, which promotes drug dissolution and absorption while avoiding burst release risk by regulating dissolution kinetics. Under this dual protection, the middle high-barrier layer can fully exert its environmental barrier function of isolating light, heat and moisture, thereby ensuring the chemical stability of tacrolimus. The entire system achieves a balance between protection, mechanical robustness and controllable release, providing an effective solution for the reliable delivery of active pharmaceutical ingredients. By expanding phospholipids from a single specification to a combination system with adjustable hydrogenation levels, the outer coating is upgraded from a passive barrier with fixed functions to a combination structure with adjustable parameters, giving the outer coating the ability to customize the release rate. This enables the regulation of the release behavior of tacrolimus microparticles, improving the formulation performance and adaptability to clinical needs. By placing three types of phospholipids in the inner and outer layers according to their functions, active compensation for individual differences in gastric emptying is achieved. The core technology utilizes the progressive dissolution characteristics of the third hydrogenated phospholipid in gastric juice to convert gastric retention time into a signal of residual thickness in the outer sublayer, thereby inversely regulating the intestinal release initiation point in the inner sublayer. Detailed Implementation

[0016] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0017] Example 1: A tacrolimus capsule, wherein the microspheres comprise a core and four layers sequentially coating the surface of the core, from the inside out as follows: The drug layer contains tacrolimus and a dispersion carrier; The inner layer is a flexible buffer layer containing a first polymer and xanthan gum in a swollen state; The intermediate layer is a high-barrier layer containing a second polymer; The outer layer is a protective controlled-release layer containing a third polymer grafted with lipophilic bile salt derivatives and phospholipids; the contents of each component in the microcapsules, by weight, are as follows: core: 180 parts, which is a microcrystalline cellulose core with a particle size of 500-600 μm; drug layer: tacrolimus: 100 parts; dispersion carrier is hydroxypropyl methylcellulose E5 (HPMC E5): 160 parts. Inner layer, flexible cushioning layer: The first polymer is hydroxypropyl methylcellulose E50 (HPMC E50): 100 parts; xanthan gum: 10 parts (molecular weight 2×10). 6 ); Intermediate layer, high barrier layer: the second polymer is ethyl cellulose EC N10: 60 parts; Outer layer, protective controlled-release layer: The third polymer is polyacrylic acid resin (Utec® E PO): 100 parts; the lipophilic bile salt derivative is sodium taurocholate: 6 parts; the phospholipid is hydrogenated soybean phospholipid (hydrogenation degree ≥90%, particle size D90 ≤ 50 μm): 10 parts.

[0018] The preparation of the protective controlled-release coating solution comprises the following steps: A1. Preparation of bile salt-polymer copolymers: a) Activation: Weigh out polyacrylic acid resin and dissolve it in anhydrous dimethyl sulfoxide. Add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC, the amount is 1.2 times the molar amount of carboxyl groups in the resin) and N-hydroxysuccinimide (NHS, the molar amount is equal to that of EDC). Stir the reaction at room temperature in the dark for 3 hours to activate the carboxyl groups. b) Grafting: Dissolve sodium taurocholate in a small amount of anhydrous dimethyl sulfoxide and add it dropwise to the above activation solution. Heat the system to 38°C and stir the reaction under nitrogen protection for 18 hours. c) Purification: The reaction solution was added dropwise into 10 times its volume of ice-cold ether to precipitate the solid. The solid was collected by filtration and washed 3 times with ice-cold ether. The solid was placed in a vacuum drying oven and dried at 40°C to constant weight. It was then pulverized and passed through a 100-mesh sieve to obtain sodium taurocholate-polyacrylic acid resin copolymer powder. A2. Preparation of the protective controlled-release layer composite coating solution: a) Premixing: Take copolymer powder and hydrogenated soybean lecithin and physically mix them in a dry container for 15 minutes; b) Dispersion and homogenization: The premix was added to a mixed solvent consisting of isopropanol and purified water in a volume ratio of 9:1 (the total amount of solvent was 10 times the total weight of solids, w / v). The mixture was first dispersed by mechanical stirring at 800 rpm for 1 hour, and then circulated 4 times at 1000 bar using a high-pressure homogenizer with the outlet temperature controlled below 25°C to obtain a stable colloidal dispersion with an opalescent blue color and a particle size distribution D90 ≤ 200 nm, which was used as the final protective controlled-release coating solution.

[0019] The specific steps for preparing the tacrolimus capsules are as follows: S1. Preparation of drug-loaded pellet cores: Tacrolimus and HPMC E5 were dissolved in a mixed solvent of anhydrous ethanol and acetone in a volume ratio of 2:1 to prepare a coating solution with a total solid content of 7%. A fluidized bed coating machine (bottom spray type) was used to coat the microcrystalline cellulose pellet cores with the drug. The process parameters were: inlet air temperature 38°C, outlet air temperature 33°C, atomization pressure 1.2 bar, material temperature maintained at 33°C, and after coating, the pellet cores were dried at an inlet air temperature of 40°C for 30 minutes to obtain the drug-loaded pellet cores. S2. Flexible Buffer Coating and Curing: Coating Solution Preparation: HPMC E50 was dispersed in purified water and stirred until dissolved. Xanthan gum was slowly added under high-speed shear (2000 rpm) and continuously sheared and dispersed for 30 minutes to obtain a uniform xanthan gum suspension. Coating Operation: Using the above-mentioned drug-loaded pellet core as a substrate, spray coating was performed in a fluidized bed. Parameters: inlet air temperature 37°C, outlet air temperature 32°C. Curing Treatment: The coated pellets were transferred to a constant temperature and humidity chamber and cured for 8 hours at 100°C and 35% RH. This process allowed the xanthan gum to fully swell and form a dense, elastic gel network structure with HPMC E50. S3, High Barrier Coating: The matured micro-pellets are returned to the fluidized bed, and ethyl cellulose is dissolved in a solvent composed of ethanol and dichloromethane in a volume ratio of 1:1 to prepare a 5% coating solution for spray coating. Process parameters: inlet air temperature 42°C, outlet air temperature 37°C. S4. Protective Controlled-Release Coating: The microparticles coated with the high-barrier layer are placed in a fluidized bed and sprayed with the composite coating liquid prepared above. Key process parameters: inlet air temperature 35°C, outlet air temperature 30°C, atomization pressure 1.5 bar. After coating, the microparticles are fluidized and dried at 32°C for 40 minutes to obtain tacrolimus multilayer coated microparticles. The final particle size distribution of the microparticles is 950-1050 μm. S5. Capsule filling: The prepared multi-layer coated microspheres are filled into opaque hydroxypropyl methylcellulose capsule shells according to the specification of 1.0 mg or 5.0 mg of tacrolimus per capsule, thus obtaining the tacrolimus capsules described in this invention.

[0020] For this embodiment, experiments were conducted with the amounts of the core, drug layer, inner layer (HPMC E50, xanthan gum), intermediate layer (EC), and outer polymer layer (Utec® E PO) kept constant. Only the amounts of lipophilic bile salt derivatives (sodium taurocholate, BS) and phospholipids (hydrogenated soybean phospholipids, PL) added to the outer layer were adjusted. The control group and experimental group were set up as shown in Table 1 below: Table 1 Experimental Grouping in Example 1

[0021] In vitro dissolution test: according to the first method (basket method) of General Chapter 0931 of the 2020 edition of the Chinese Pharmacopoeia.

[0022] Medium: First, the experiment was conducted in 900 mL of simulated gastric fluid (pH 1.2, without enzymes) for 2 hours, and then transferred to 900 mL of simulated intestinal fluid (pH 6.8, containing 0.5% sodium dodecyl sulfate to maintain the trough conditions) for another 4 hours at a temperature of 37±0.5°C and a rotation speed of 50 rpm.

[0023] Samples are taken at preset time points to calculate the cumulative release rate.

[0024] Tacrolimus is available in 1 mg strength, with a total dissolution medium volume of 900 mL;

[0025] The formula for cumulative release rate is: Cumulative release rate over 2 hours (in the stomach): ; Cumulative release rate over 4 hours (intestinal tract): ; Cumulative release rate over 6 hours (intestinal tract): ; Where Rt is the cumulative release rate (%) at time t, Ct is the drug concentration (μg / mL) measured at time t, 900 is the initial volume of dissolution medium (mL), 1000 is the mass of tacrolimus (1000μg), and 10 is the volume of fresh medium added after 4 hours of sampling (mL). The test results are shown in Table 2 below: Table 2 Results of in vitro dissolution test in Example 1

[0026] Surface wettability determination: The static contact angle of a single microparticle under different media droplets was measured using a contact angle meter.

[0027] Media: simulated gastric juice (SGF, pH 1.2) and simulated intestinal juice (SIF, pH 6.8).

[0028] Each sample was measured 10 times and the average value was taken.

[0029] The test results are shown in Table 3 below: Table 3 Results of surface wettability test

[0030] The contact angle was significantly reduced in the groups containing bile salts (control group B and experimental groups 1-2). This study demonstrates that bile salts effectively improve the wettability of the microsphere surface, facilitating water penetration and drug dissolution.

[0031] Micellarization ability and equilibrium solubility determination: Excess tacrolimus raw material was mixed with microsphere extracts of different groups. (Take the microspheres prepared in Example 1, peel off and collect their outermost layer (i.e., the protective controlled-release layer) material, and dissolve it in SIF.) Incubation lasts for 24 hours. Centrifuge and collect the supernatant to determine the equilibrium solubility.

[0032] The test results are shown in Table 4 below: Table 4 Results of micellization ability and solubility determination

[0033] The extracts from experimental groups 1-2 showed the strongest solubilizing ability, significantly higher than the single-component groups. This study demonstrates that BS and PL form more efficient and stable mixed micelles in solution, exhibiting a synergistic solubilizing effect and significantly improving bioavailability.

[0034] Microsphere friability and compressive strength test: Friability test: Refer to the tablet friability test method.

[0035] Take about 10.0g of microcapsules and place them in a smooth, round glass bottle (with a baffle). Rotate the bottle at 25 rpm for 1000 revolutions (about 40 minutes).

[0036] After removal, the fine powder was sieved through a 230-mesh sieve (63μm aperture), the weight of the remaining microspheres was weighed, and the percentage of weight loss was calculated.

[0037] Single pellet compressive strength test: Using a texture analyzer, 30 microspheres with uniform particle size were randomly selected, and the maximum force (N) when they were crushed was measured. The mean and standard deviation were then calculated.

[0038] Tests showed that the friability (weight loss%) of control group A was 5.8 ± 0.6%, and the average compressive strength (N / ball) was 3.2 ± 0.5 N. The friability (weight loss%) of control group B was 4.5 ± 0.5%, and the average compressive strength (N / ball) was 4.1 ± 0.6 N. The control group C had a friability (weight loss%) of 2.5 ± 0.4% and an average compressive strength (N / ball) of 7.8 ± 1.0 N. The friability (weight loss%) of experimental groups 1-2 was 1.2±0.3, and the average compressive strength (N / ball) was 9.5±1.5. The microspheres have high strength, and when they break, the outer layer deforms rather than shatters instantly, producing almost no dust, demonstrating an improvement in strength and toughness.

[0039] The technical solutions described in the embodiments of this application have at least the following technical effects or advantages: By constructing a multi-layered coated microsphere system with functional gradients, the inherent physicochemical defects of tacrolimus and the technical problems encountered in its dosage form are solved. Lipophilic bile salt derivatives and phospholipids are introduced as key functional components in the outer layer, and a specific curing process is used for the inner layer xanthan gum.

[0040] The introduction of bile salt derivatives is mainly aimed at improving the extreme hydrophobicity of the microsphere surface by utilizing their amphiphilic molecular structure, significantly reducing their interfacial tension in gastrointestinal fluid, thereby promoting the penetration of the hydration medium into the coating layer and creating initial conditions for drug dissolution.

[0041] At the same time, as an endogenous absorption enhancer, it can interact with drug molecules in the body fluid environment, assisting in the formation of micelles or mixed micelles, directly improving the solubility and membrane permeability of tacrolimus.

[0042] The introduction of phospholipids plays a crucial role in regulation and stabilization.

[0043] The aim is to form a more ordered and stable composite assembly with bile salt derivatives through intermolecular hydrophobic interactions and hydrogen bonds in the coating layer and at the dissolution interface.

[0044] This composite structure can effectively regulate the penetration rate of water molecules and the relaxation and swelling process of the coating polymer chains, thereby enabling programmed control of drug release kinetics.

[0045] This transforms the release behavior from an uncontrollable rate of release to a smooth, predictable, and gradual release.

[0046] Experimental results confirm that When the two are combined in an appropriate ratio (e.g., 6:10), It retains the advantages of bile salts in improving wetting and solubility. Furthermore, the release rate in the stomach is controlled to a low and safe level through the buffering mechanism of phospholipids. It also achieved complete and stable release in the intestinal environment, with a significant synergistic effect.

[0047] Meanwhile, the xanthan gum used in the inner layer swells and forms a dense and elastic three-dimensional hydrated gel network after being cured under high temperature and low humidity conditions.

[0048] This structure provides the entire microsphere with excellent mechanical cushioning properties. It can effectively absorb and disperse external physical stress. Protect the intermediate high-barrier layer (such as ethyl cellulose) from brittle fracture.

[0049] This design directly addresses and overcomes the technological challenges of high-barrier materials, such as insufficient mechanical strength and susceptibility to damage during transportation.

[0050] Example 2: The above example adopts a synergistic design at the molecular and material levels. The inner layer of cured xanthan gum network ensures the physical integrity of the dosage form and solves the problem of mechanical fragility. The outer bile salt-phospholipid complex system creates a smart responsive interface, promoting drug dissolution and absorption. By regulating the dissolution kinetics, the risk of sudden release was avoided. Under this dual protection, the intermediate high-barrier layer was able to fully exert its role as an environmental barrier against light, heat, and moisture. This ensures the chemical stability of tacrolimus, achieving a balance between protective properties, mechanical robustness, and controllable release in the entire system. It provides an effective solution for the reliable delivery of active pharmaceutical ingredients.

[0051] To further improve its delivery performance, further improvements were made based on Example 1.

[0052] The phospholipids include first, second and third phospholipids with different degrees of hydrogenation; in, The first hydrogenated phospholipid is hydrogenated soybean phospholipid (HSPC), with a hydrogenation degree ≥90% and a phase transition temperature (Tm) of 55℃. This component is in a highly ordered gel state at physiological temperature, with strong hydrophobicity and slow hydration. The second hydrogenated phospholipid is a partially hydrogenated soybean phospholipid with a hydrogenation degree of 40-60% and a Tm of 35-45℃. It is in the transition range between gel and liquid crystal states within the gastrointestinal temperature range, and has both structural stability and dynamic responsiveness. The third type of hydrogenated phospholipid is non-hydrogenated soybean phospholipid (PC) with a hydrogenation degree ≤5% and a Tm below 0°C.

[0053] This component remains in a fluid liquid crystal state under physiological conditions, exhibits strong hydrophilicity, and is easily and rapidly hydrated and blended.

[0054] Three phospholipids with different degrees of hydrogenation were placed in a mixing container in a predetermined ratio and mixed evenly by mechanical stirring to obtain a phospholipid mixture, which was then added to the coating solution as a phospholipid component.

[0055] Experiments were conducted on the technical solution of this embodiment, based on experimental groups 1-2 of Embodiment 1, with only the hydrogenation type and ratio of phospholipids changed, as shown in Table 5 below: Table 5 Experimental Grouping in Example 2

[0056] The test results are shown in Table 6 below: Table 6 Results of in vitro dissolution test in Example 2

[0057] T50% is the time required for the cumulative release rate in the intestine to reach 50%.

[0058] Dynamic swelling rate determination: at specific time points (0.5, 2, 4, 6 hours) during the dissolution experiment. Use a fine sieve to scoop out 20 intact micro-pills. Quickly blot the surface liquid with filter paper and immediately measure its diameter.

[0059] Calculate: Swelling rate (%) = [(D t - D0) / D0] × 100%, Where D0 is the average diameter of the initially dried microspheres. D t The diameter after swelling at each time point.

[0060] The test results are shown in Table 7 below: Table 7. Results of dynamic swelling rate determination in Example 2 (swelling rate %)

[0061] The technical solutions described in the embodiments of this application have at least the following technical effects or advantages: This embodiment introduces three phospholipids with different degrees of hydrogenation for compounding. By controlling the phase transition temperature and membrane fluidity of the phospholipids, the swelling-erosion behavior of the outer coating of the microparticles can be regulated, which solves the limitation that a single degree of hydrogenation of phospholipids cannot simultaneously meet the different release rate requirements of different clinical scenarios.

[0062] From a technical perspective, phospholipids with different degrees of hydrogenation exhibit differentiated aggregate structures at physiological temperatures.

[0063] The first hydrogenated phospholipid (hydrogenation degree ≥90%, Tm≈55℃) is in a highly ordered gel state at 37℃. Its hydrophobic acyl chains are tightly arranged, and the complex assembly formed with bile salt molecules has a dense structure and a high hydration energy barrier. It mainly contributes to the hydrophobic barrier and structural rigidity of the coating layer, delaying water penetration and polymer swelling.

[0064] Third-generation hydrogenated phospholipids (hydrogenation degree ≤5%, Tm < 0℃) are always in a flowing liquid crystal state under physiological conditions. They have a high degree of freedom of molecular motion, and their polar head groups are easy to form hydrogen bonds with water molecules. They can quickly initiate interfacial hydration and form hydrophilic channels in conjunction with bile salts, significantly reducing the dissolution activation energy.

[0065] Second hydrogenated phospholipids (hydrogenation degree 40-60%, Tm 35-45℃) exist in the range of coexistence of gel and liquid crystal states. Their molecular chain segments can undergo reversible phase transitions under gastrointestinal temperature fluctuations, combining structural stability and environmental responsiveness. In composite systems, they play a buffering and regulating role in connecting rigid and flexible regions.

[0066] When three phospholipids are co-assembled in different proportions, they can form phase-separated or continuous phase gradient distribution structural features at the nanoscale, thereby changing the water diffusion coefficient, stress relaxation rate and dissolution front propagation mode of the coating layer as a whole.

[0067] Experimental results show that the release behavior of microparticles can be controlled by adjusting the ratio of the three phospholipids.

[0068] The first-hydrogenated phospholipid-dominant formulation (experimental group 2-1) reduced the 2-hour release rate in the stomach to 2.5%, extended the T50% to 4.8 hours, and maintained a low swelling rate throughout, confirming that it forms an effective delayed-release structure, suitable for patients who need to reduce gastric irritation or have rapid gastric emptying.

[0069] The predominantly tertiary phospholipid ratio (experimental groups 2-3) significantly accelerated the release rate, increasing the gastric release rate to 11.5%, shortening the T50% to 2.8 hours, and enabling rapid swelling initiation, making it suitable for clinical scenarios requiring rapid attainment of therapeutic concentrations.

[0070] The balanced formulation with second-hydrogenated phospholipids as the core (experimental group 2-2) exhibits the linear release characteristics closest to zero order. The swelling rate-time curve and the release rate-time curve both show good linear correlation, making it suitable for long-term treatment that requires maintaining stable blood drug concentrations.

[0071] The swelling and release behaviors of each experimental group showed a high degree of consistency, proving that the release kinetics are physically controlled by the hydration-swelling-dissolution process of the coating layer, and the degree of phospholipid hydrogenation is the core variable regulating this process.

[0072] Example 3: The above embodiments expand phospholipids from a single specification to a combined system with adjustable hydrogenation levels, upgrading the outer coating from a passive barrier with fixed function to a combined structure with adjustable parameters, thus endowing the outer coating with the ability to customize the release rate. This enabled the regulation of tacrolimus microsphere release behavior, improving formulation performance and adaptability to clinical needs.

[0073] In actual clinical practice, patients' gastric emptying time can range from 30 minutes to 2 hours. The release initiation time of microspheres with a fixed ratio after entering the intestine varies significantly. Therefore, the microspheres need to be adjusted accordingly.

[0074] The outer layer comprises an outer sublayer and an inner sublayer, wherein the third hydrogenated phospholipid accounts for 80% of the total phospholipids in the outer sublayer and the second hydrogenated phospholipid accounts for 20%; In the inner sublayer, the first hydrogenated phospholipid accounts for 80% of the total phospholipids in the inner sublayer, and the second hydrogenated phospholipid accounts for 20%. The dry weight ratio of the outer sublayer to the inner sublayer is 9:11. During the protective controlled-release coating process, the inner sublayer coating solution is prepared using phospholipid mixture A (80% first hydrogenated phospholipid and 20% second hydrogenated phospholipid). The outer sublayer coating solution was prepared using phospholipid mixture B (80% tertiary hydrogenated phospholipid and 20% tertiary hydrogenated phospholipid); During the protective controlled-release coating process, the inner sublayer is first increased in weight to the target (outer layer total dry weight 55%), and then dried for 15 minutes. Then coat the outer sublayer: Use the same coating process parameters as the inner sublayer, namely, inlet air temperature 35°C, outlet air temperature 30°C, atomization pressure 1.5 bar, increase weight to the target (outer layer total dry weight 45%), and dry for 40 minutes.

[0075] Experiments were conducted on the technical solution of this embodiment and experimental group 2-2 of embodiment 2 to verify the differences in the intestinal release initiation point under different gastric retention times.

[0076] In Example 2, experimental group 2-2 served as control group E. In Example 3, experimental group 3-1 was set up. The outer layer of experimental group 3-1 included an outer sublayer and an inner sublayer. The third hydrogenated phospholipid in the outer sublayer accounted for 80% of the total phospholipids in the layer, and the second hydrogenated phospholipid accounted for 20%. The first hydrogenated phospholipid in the inner sublayer accounts for 80% of the total phospholipids in the layer, and the second hydrogenated phospholipid accounts for 20% of the total phospholipids in the layer. The dry weight ratio of the outer sublayer to the inner sublayer is 9:11.

[0077] Dissolution determination at different times: according to the first method (basket method) of General Chapter 0931 of the 2020 edition of the Chinese Pharmacopoeia.

[0078] Medium: First, run in 900 mL of simulated gastric fluid (pH 1.2, without enzymes) for 30 minutes or 120 minutes respectively (simulating fast and slow gastric emptying), then transfer to 900 mL of simulated intestinal fluid (pH 6.8, containing 0.5% sodium dodecyl sulfate to maintain the trough conditions) and continue running for 6 hours at a temperature of 37±0.5°C and a speed of 50 rpm.

[0079] Samples were taken at preset time points to calculate the cumulative release rate and T50% (the time required for 50% release into the intestines).

[0080] Observation of residual thickness of outer sublayer: At the end of the gastric phase (30 minutes or 120 minutes), 20 microspheres were taken from each group, freeze-dried, embedded and sectioned, and the thickness of outer sublayer was measured to calculate the residual percentage relative to the initial thickness.

[0081] The test results are shown in Table 8 below: Table 8 Experimental Detection Results of Example 3

[0082] Example 3: The outer double-layer structure successfully achieved self-compensation for gastric emptying time: In patients with slow gastric emptying (120 minutes), the residual thickness of the outer sublayer was significantly reduced (40%), and the intestinal T50% was shortened (3.6 hours); in patients with fast gastric emptying (30 minutes), the outer sublayer remained intact (85%), and the intestinal T50% was correspondingly prolonged (4.2 hours). The difference in T50% between the two groups was only 0.6 hours, which was 50% lower than the 1.2 hours in the control group E. The cumulative release rate at 6 hours was >95% in all groups, and the completeness of release was not affected by the double-layer structure.

[0083] The technical solutions described in the embodiments of this application have at least the following technical effects or advantages: The improvements in Example 3 address the issue of fluctuating efficacy caused by individual differences in gastric emptying time in patients with oral solid sustained-release formulations. Tacrolimus microgranules face physiological variations in gastric emptying rates, ranging from 30 minutes to 2 hours, in clinical applications. Traditional fixed-ratio controlled-release coatings cannot respond to these variations, resulting in a significant drift in the release initiation point after the drug enters the intestine, affecting the predictability of blood drug concentrations and therapeutic stability.

[0084] The technical principle of this scheme is based on the essential difference in the hydration rate of phospholipids with different degrees of hydrogenation. The third-hydrogenated phospholipid has a phase transition temperature below 0°C and remains in a flowing liquid crystal state under physiological conditions. Its polar head groups have a strong affinity for water molecules, allowing for rapid hydration and gradual dissolution. The first-hydrogenated phospholipid has a phase transition temperature of approximately 55°C and exhibits a highly ordered gel state at 37°C. Its acyl chains are densely arranged, making it difficult for water molecules to penetrate, and its swelling initiation is extremely slow. Utilizing this difference, the outer controlled-release layer is reconstructed into a functionally differentiated bilayer structure: the outer sublayer, dominated by the third-hydrogenated phospholipid, is positioned as a gastric juice-responsive sensor, with its thickness decreasing as gastric retention time increases; the inner sublayer, dominated by the first-hydrogenated phospholipid, is positioned as an intestinal release actuator, remaining inert in gastric juice. The two layers are connected by a second-hydrogenated phospholipid to achieve component transition and interface fusion, ensuring structural integrity.

[0085] When the microparticles enter the gastric juice, the outer sublayer immediately initiates hydration and continues to slowly dissolve, with its residual thickness showing a clear negative correlation with gastric emptying time. In cases of rapid gastric emptying, the outer sublayer remains intact, with a residual thickness exceeding 85% of the initial value; in cases of slow gastric emptying, the outer sublayer dissolves more thoroughly, with the residual thickness decreasing to around 40%. This residual thickness constitutes a physical memory signal for gastric retention time. After the microparticles enter the intestinal environment, water must pass through the residual outer sublayer and the second hydrogenated phospholipid transition region to reach the inner sublayer and trigger its swelling. The greater the residual thickness of the outer sublayer, the longer the water permeation path, and the longer the time required for the inner sublayer to reach the critical hydration threshold; conversely, the smaller the residual thickness of the outer sublayer, the lower the water permeation resistance, and the faster the dissolution of the inner sublayer begins. This forms a negative feedback regulatory loop between gastric emptying time and the intestinal release initiation point.

[0086] This embodiment places three types of phospholipids in the inner and outer layers according to their functions, achieving active compensation for individual differences in gastric emptying. The core technology is to utilize the progressive dissolution characteristics of the third hydrogenated phospholipid in gastric juice to convert the gastric retention time into a signal of the residual thickness of the outer sublayer, thereby inversely regulating the intestinal release initiation point of the inner sublayer.

[0087] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing tacrolimus capsules, characterized in that, Includes the following steps: S1. Preparation of drug-loaded pellet cores: Tacrolimus and hydroxypropyl methylcellulose E5 are dissolved in an organic solvent to prepare a coating solution. The pellet cores are coated with the drug using a fluidized bed and then dried to obtain drug-loaded pellet cores. S2, Flexible buffer layer coating and curing: The first polymer is dissolved in water, xanthan gum is added and dispersed evenly, and the drug-loaded pellet core is coated using a fluidized bed. After drying, the pellets are cured for 8 hours at a temperature of 100 °C and a relative humidity of 35% to obtain cured pellets. S3, High Barrier Coating: The second polymer is dissolved in an organic solvent, and the matured microcapsules are coated in a fluidized bed to obtain high barrier coated microcapsules. S4. Protective controlled-release coating: A coating solution is prepared by combining a third polymer grafted with lipophilic bile salt derivatives and phospholipids. The high-barrier microspheres are coated using a fluidized bed and then dried to obtain multi-layer coated microspheres. The phospholipids are a complex system of phospholipids with different degrees of hydrogenation, including a first hydrogenated phospholipid, a second hydrogenated phospholipid, and a third hydrogenated phospholipid; the first hydrogenated phospholipid has a degree of hydrogenation ≥90% and a phase transition temperature of 55℃; the second hydrogenated phospholipid has a degree of hydrogenation 40-60% and a phase transition temperature of 35-45℃; the third hydrogenated phospholipid has a degree of hydrogenation ≤5% and a phase transition temperature below 0℃. Its mass ratio includes: 70% first hydrogenated phospholipid, 25% second hydrogenated phospholipid, and 5% third hydrogenated phospholipid; or 30% first hydrogenated phospholipid, 50% second hydrogenated phospholipid, and 20% third hydrogenated phospholipid; or 10% first hydrogenated phospholipid, 30% second hydrogenated phospholipid, and 60% third hydrogenated phospholipid. S5. Capsule filling: The obtained multi-layer coated microspheres are filled into capsule shells; The first polymer is hydroxypropyl methylcellulose E50, the second polymer is ethyl cellulose, the third polymer is polyacrylic acid resin, and the lipophilic bile salt derivative is sodium taurocholate.

2. The method for preparing tacrolimus capsules as described in claim 1, characterized in that, The content of each component, by weight, is as follows: 180 portions of pellet core; 100 doses of tacrolimus; Hydroxypropyl methylcellulose E5 160 parts; 100 parts of the first polymer; 10 parts xanthan gum; 60 parts of the second polymer; 100 parts of the third polymer; Lipophilic bile salt derivatives, 2-10 parts; Phospholipids 5-15 parts.

3. The method for preparing tacrolimus capsules as described in claim 1, characterized in that, The preparation of the coating solution for protecting the controlled-release layer in step S4 includes: A1. Preparation of bile salt-polymer copolymer: The third polymer was dissolved in a solvent, activated, and then reacted with a lipophilic bile salt derivative at 38°C for 18 hours. The copolymer was then purified, dried, and pulverized to obtain copolymer powder. A2. Preparation of coating solution: The copolymer powder is mixed with phospholipids and added to a mixed solvent composed of isopropanol and water in a volume ratio of 9:

1. After homogenization at 1000 bar pressure, a colloidal dispersion with a particle size D90 ≤200 nm is obtained, which is the protective controlled-release coating solution.

4. The method for preparing tacrolimus capsules as described in claim 1, characterized in that, The protective controlled-release layer described in step S4 includes an inner sublayer and an outer sublayer; The inner sublayer is enriched with first hydrogenated phospholipids, and the outer sublayer is enriched with third hydrogenated phospholipids; In the inner sublayer, the first hydrogenated phospholipid accounts for 80% of the total phospholipids in the inner sublayer, and the second hydrogenated phospholipid accounts for 20%. In the outer sublayer, the third hydrogenated phospholipid accounts for 80% of the total phospholipids in the outer sublayer, and the second hydrogenated phospholipid accounts for 20%. The dry weight ratio of the outer sublayer to the inner sublayer is 9:

11.

5. The method for preparing tacrolimus capsules as described in claim 4, characterized in that, In step S4, a double-layer coating process is used: first, the inner sublayer is coated, and the coating weight is increased to 55% of the total dry weight of the protective controlled-release layer, and then dried for 15 minutes; then, the outer sublayer is coated, and the coating weight is increased to 45% of the total dry weight of the protective controlled-release layer, and then dried for 40 minutes.

6. The method for preparing tacrolimus capsules as described in claim 1, characterized in that, The fluidized bed coating process parameters are: inlet air temperature 35-42℃, outlet air temperature 30-37℃, and atomization pressure 1.2-1.5 bar; In the fluidized bed coating process, the drying temperature is 30-40℃ and the drying time is 15-40 minutes.

7. The method for preparing tacrolimus capsules as described in claim 1, characterized in that, The core pellet has a particle size of 500-600 μm, and the multi-layer coated micro-pellets have a particle size of 950-1050 μm.

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