High-stability low-irritation oxytetracycline long-acting injection and preparation method thereof

Abstract

The application discloses a high-stability and low-irritation oxytetracycline long-acting injection and a preparation method thereof. 2+ EDTA-2Na and sodium formaldehyde bisulfite are coordinated to stabilize, and forsythia extract reduces irritation; the pH of the finished product is 8.2-8.8. The method comprises acid pre-coordination, pre-filtration, ultrafiltration, reduction and deoxygenation (dissolved oxygen is less than or equal to 2 ppm) and 0.22 mu m terminal sterile filtration. The application realizes long-term clarification and content stability under high loading, and inhibits metal catalytic oxidation and alkali-sensitive degradation.

Description

Technical Field

[0001] This invention relates to the technical field of veterinary injectable preparations, and in particular to a highly stable, low-irritation long-acting oxytetracycline injection and its preparation method. Background Technology

[0002] Oxytetracycline is a broad-spectrum tetracycline antibiotic that inhibits various pathogens, including Gram-positive and Gram-negative bacteria, as well as mycoplasma and chlamydia, and is widely used in the prevention and treatment of bacterial diseases in livestock and poultry. However, the oxytetracycline molecule contains multiple phenolic hydroxyl and carboxyl active sites, which readily form coordination complexes with metal ions. Furthermore, it is prone to degradation or discoloration under light, heat, and oxidation conditions, leading to a decrease in the content of the active ingredient and reduced formulation stability.

[0003] To improve the duration of action of oxytetracycline in vivo, current technologies typically employ oil-based injectable solutions or high-concentration aqueous solutions. However, these formulations generally suffer from limited solubility, easy crystallization, color deepening, and instability in clarity during long-term storage. Some formulations add highly polar solvents or organic amine modifiers to improve solubility, but these often result in strong muscle irritation, leading to adverse reactions such as redness, swelling, induration, and even necrosis at the injection site, making it difficult to balance stability and safety.

[0004] Furthermore, trace metal ions (such as iron and copper) in oxytetracycline solutions readily catalyze oxidation reactions, promoting their degradation and generating chromogenic substances. Under weakly alkaline conditions, oxytetracycline molecules may also undergo ring-opening and condensation reactions, accelerating impurity formation. Therefore, existing literature has proposed using chelating agents or antioxidants for stabilization treatment; however, single components often struggle to simultaneously address the needs of metal ion scavenging and free radical inhibition, resulting in limited stabilization effects.

[0005] On the other hand, the local irritation of tetracycline injections during injection has always been a concern in clinical practice. Existing improvements mainly focus on adjusting solvent ratios or surfactants, lacking systematic research on the complexation balance of drugs at high concentrations and the control of system viscosity. A formulation system that can maintain high content while also ensuring low irritation and high stability has not yet been established.

[0006] In summary, existing oxytetracycline injections still suffer from problems such as insufficient solubility, easy crystallization, rapid color change, poor long-term stability, and strong injection irritation. There is an urgent need for an improved long-acting formulation that can achieve stable dissolution under high concentration conditions, long-term clarity, and significantly reduce irritation. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned problems existing in the prior art and to provide a highly stable, low-irritation long-acting oxytetracycline injection and its preparation method.

[0008] To achieve the above objectives, the first aspect of the present invention provides a highly stable and low-irritation long-acting oxytetracycline injection, comprising the following components per 100 mL of the preparation: 20-35g of oxytetracycline; 30-45 mL of 2-pyrrolidone; 15-25 mL of propylene glycol; Disodium ethylenediaminetetraacetate 0.10–0.50 g; Sodium formaldehyde sulfoxylate 1.0–2.0 g; Magnesium salts or magnesium oxide according to Mg 2+ 0.15 to 0.35 equivalents of oxytetracycline molar amount; Forsythia extract 0.20-0.60g, wherein the forsythia extract contains 2-8mg / 100mL of forsythoside; During the stabilization stage, a 10%–20% (w / w) monoethanolamine solution was used to adjust the pH so that the pH of the finished product was controlled at 8.2–8.8. The remaining volume is made up to 100 mL with water for injection; The formulation is sterile filtered through a 0.22μm terminal filter, and the dissolved oxygen level is ≤2ppm before filling.

[0009] This invention limits the amount of the mixed solvent of 2-pyrrolidone and propylene glycol, enabling oxytetracycline to achieve stable dissolution and significantly reduce crystallization tendency under high loading (20-35 g / 100 mL). This combination maintains moderate system viscosity and diffusion rate while ensuring solvation capability, reducing particle germination caused by local supersaturation. This results in stable product clarity, reduced visible foreign matter incidence, and subvisible particles within a controlled range.

[0010] Magnesium salts or magnesium oxide form Mg-OTC coordination complexes with oxytetracycline, which are the core carriers for its long-lasting properties. This complexation behavior is strongly influenced by solvent polarity and pH. Without propylene glycol to moderate the dielectric constant of the system, Mg... 2+ Excessive coordination promotes an increase in solution viscosity and crystal nucleation; without the solvation effect of 2-pyrrolidone, Mg... 2+ Incomplete binding with oxytetracycline leads to decreased stability.

[0011] Magnesium salts or magnesium oxide according to Mg 2+ The amount of 0.15 to 0.35 equivalents involved in coordination reduces the exposure of free polyphenol ketone groups and amino alcohol sites within the preferred range, inhibiting ring-opening and condensation side reactions and complexation-induced precipitation under alkaline conditions. When the amount of equivalents is too low, the complexation is insufficient, and when it is too high, particle formation is induced. Within this range, a more concentrated and low-level distribution of insoluble particles and better clarification stability can be obtained.

[0012] The combined use of disodium ethylenediaminetetraacetate and sodium formaldehyde sulfoxylate achieves a dual-channel stabilization effect: first, chelation to remove trace metal catalytic centers, and then reduction to inhibit chromogen radical chains. Under the solvent and magnesium coordination context of this invention, this combination exhibits a non-additive advantage in inhibiting color and related substances; under accelerated conditions, the growth rates of A350 and A500 and the increase in impurity peak area are significantly lower than the single-agent stabilization control.

[0013] Adjust the final pH to 8.2–8.8 to achieve an optimal balance between coordination equilibrium, solubility, and alkali-sensitive degradation. A pH below this range will result in insufficient solubility and coordination stability, while a pH above this range will accelerate apparent degradation and increase color. Within this range, a stable state with high content retention and pH shift less than a predetermined threshold can be achieved.

[0014] Forsythia extract at concentrations of 0.20–0.60 g (calculated as forsythoside 2–8 mg / 100 mL) remains clear and compatible in both highly polar solvents and alkaline systems, without introducing new risks of crystallization or turbidity. In physicochemical and model evaluations related to intramuscular injection, local irritation-related indicators (such as redness and swelling scores, exudate volume, or inflammatory factor levels) are lower than in the control without this component, demonstrating a low-dose irritation mitigation effect under the pH and solvent ratio conditions of this system, while maintaining color and particle control. Forsythia extract not only serves as an excipient to reduce irritation but also exhibits synergistic effects with magnesium complexation and pH status. The lignans and glycosides in forsythia extract contain phenolic hydroxyl groups and ether bonds, forming a partially ionized state in pH 8.2–8.8 and highly polar solvents, which can react with free magnesium... 2+ Or, the weak complexation on the surface of oxytetracycline molecules can provide a certain degree of shielding.

[0015] Controlling dissolved oxygen to ≤2 ppm before filling and implementing 0.22 μm terminal filtration simultaneously suppresses the generation of oxidation-related impurities and the proliferation of subvisible particles; combined with inert headspace, it further delays early discoloration and improves the consistency between acceleration and long-term stability.

[0016] As a further improvement of the present invention, the water-soluble solvent system of the injection solution is composed of 2-pyrrolidone, propylene glycol and water, wherein the volume ratio of 2-pyrrolidone to propylene glycol is 1.4 to 2.5:1, and 2-pyrrolidone accounts for 30% to 44% of the total volume of the water-soluble solvent system, and propylene glycol accounts for 16% to 24% of the total volume of the water-soluble solvent system.

[0017] By employing the above technical solution, a synergistic balance was achieved between the solvent system's solubility, viscosity, and injection irritation. This ratio ensures that the coordination complex formed by oxytetracycline and magnesium ions maintains high solubility and clear stability, while the system has moderate viscosity and an osmotic pressure close to the physiological range, significantly reducing local irritation after intramuscular injection. After an accelerated stability test at 40 °C, the system showed no crystallization or discoloration, and the clarity was A. 350 A value below 0.15 indicates that this ratio range can improve the physicochemical stability and safety of the formulation while ensuring long-term drug release.

[0018] As a further improvement of the present invention, the mass ratio of disodium ethylenediaminetetraacetate to sodium formaldehyde sulfoxylate is 1:6 to 12, and the order in which the two are added during the preparation process is specified as follows: disodium ethylenediaminetetraacetate is added first, followed by sodium formaldehyde sulfoxylate.

[0019] EDTA-2Na preferentially chelates free Fe in the system upon addition. 3+ Cu 2+ Trace amounts of metal ions are used to prevent them from competitively complexing with the carboxyl group of oxytetracycline; if Mg is not present... 2+ Pre-complexation with EDTA leads to direct reaction with oxytetracycline, resulting in solution instability. However, in the system of this invention, Mg... 2+ The presence of EDTA-2Na first occupies the key coordination site, and EDTA only removes exogenous metals, keeping the system clear. The subsequent addition of sodium formaldehyde sulfoxylate, as a mild reducing agent, effectively blocks the free radical oxidation chain reaction in an environment without free metal catalysis. The synergistic stabilizing effect of the two in their order of addition is demonstrated. Accelerated tests show that, under the same pH conditions, EDTA-2Na alone or Rongalite alone results in a higher color increase rate, while the A350 / A500 increase rate decreases by approximately 40%–60% when used in combination, demonstrating non-additive stability.

[0020] As a further improvement of the present invention, the magnesium source salt is one or two of magnesium chloride, magnesium acetate or magnesium oxide.

[0021] The use of the above three magnesium sources, either individually or in combination, allows for the regulation of the release rate of magnesium ions and the types of anions in the local microenvironment during preparation and storage. The high solubility of magnesium chloride facilitates the rapid establishment of coordination equilibrium between oxytetracycline and magnesium. Magnesium acetate, with its buffering and weak coordination effects, can mitigate the risk of protein-like impurity aggregation caused by high ionic strength. Magnesium oxide gradually dissolves during the weak acidification stage, providing a source of magnesium for delayed release and consuming free hydrogen ions, thereby reducing the tendency for discoloration and precipitation caused by secondary acidification.

[0022] As a further improvement of the present invention, the injection solution further contains an organic acid stabilizer, wherein the organic acid stabilizer is selected from one or two of citric acid, malic acid, and tartaric acid, and the total concentration based on the acid radical is 0.05-0.25 mol / L; the organic acid and Mg 2+ The molar ratio of feed ingredients is 0.3–1.2:1, with oxytetracycline and Mg... 2+ The molar ratio of feed is 2.9 to 6.6:1.

[0023] By adopting the above technical solution, the system forms a ternary micro-complexation and weak buffering zone centered on magnesium. Within this zone, free magnesium ions are not excessive, avoiding over-occupation of the active sites of oxytetracycline and preventing salting out or pH fluctuations caused by excessively high concentrations of organic acid salts. Furthermore, the above molar ratio limitation exhibits a non-linear optimal window effect: exceeding the upper limit results in visible particles and a rapid increase in color; below the lower limit, the antioxidant and anti-chelation interference capabilities are insufficient; within the defined range, particle formation is controlled, the formulation color is stable, the accumulation rate of related substances is reduced, long-term storage clarity is maintained, and local irritation events after injection are significantly reduced.

[0024] As a further improvement of the present invention, the pH adjuster is a monoethanolamine solution with a mass fraction of 10% to 20%.

[0025] The pH-adjusting effect of monoethanolamine solution also acts as a buffer. When Mg 2+ When coordination is adequate, the system is insensitive to pH changes; monoethanolamine can smoothly raise the pH without inducing precipitation; if Mg 2+ Insufficient solvent or slightly overly alkaline solvent can lead to the formation of insoluble complex salts. Therefore, the use of monoethanolamine must be limited in conjunction with the solvent and magnesium equivalent to ensure the chemical and physical stability of oxytetracycline.

[0026] As a further improvement of the present invention, the pH adjuster is a mixture of monoethanolamine and N-methyldiethanolamine, and the injection solution also contains lactose monohydrate; The mass ratio of N-methyldiethanolamine to lactose monohydrate is 3–8:1, and the two together account for 0.30–1.20 wt% of the total mass of the injection solution. N-methyldiethanolamine accounts for 30–60 wt% of the total mass of the pH adjuster.

[0027] When monoethanolamine and N-methyldiethanolamine are combined, their differences in alkalinity and hydrophilicity form a synergistic buffer, stabilizing the pH of the final product and reducing the transient irritation of tissues by free amines without increasing the total amine dosage. The addition of lactose monohydrate further enhances the solubilized water structure and hydrogen bond network, and the low level of isotonic regulation helps reduce the osmotic pressure gradient at the moment of injection. Furthermore, by limiting the proportions, a compatibility window with the lowest irritation and slowest color increase can be obtained, manifested as reduced injection force, decreased pain scores, reduced levels of local inflammatory mediators, and inhibited formation of related impurities during long-term storage.

[0028] As a further improvement of the present invention, the apparent viscosity of the injection solution is 15-25 mPa·s at 25 °C and at a shear rate of 10-100 s⁻¹. -1 Within the interval, it conforms to the power-law rheological model, with the rheological index n ranging from 0.60 to 0.90.

[0029] The second aspect of the present invention provides a method for preparing the highly stable and low-irritation long-acting oxytetracycline injection as described above, comprising the following steps: S1: under conditions of 45-65°C, oxytetracycline is dissolved in a mixed solvent of 2-pyrrolidone, propylene glycol and water for injection, a magnesium source is added and the pH of the solution is adjusted to 5.3-5.8 with acid, and the solution is stirred for 30-60 min to form a pre-coordinated solution; S2: The solution obtained in step S1 is sequentially pre-filtered with 0.45 μm and treated with an ultrafiltration membrane with a molecular weight cutoff of 10-30 kDa, with a transmembrane pressure of 0.10-0.30 MPa, a temperature of 20-30 °C, and a volume concentration factor of 2-6 times. The permeate is discarded and the retained solution is collected. S3: Under nitrogen protection, add disodium ethylenediaminetetraacetate to the retention solution and stir at 55-65°C for 10-30 min; then add sodium formaldehyde sulfoxylate and stir for 10-30 min; adjust the pH to 8.2-8.8 with monoethanolamine. S4: Add the Forsythia extract solution that meets the aforementioned indicators to the solution obtained in step S3 and stir until homogeneous; use nitrogen bubbling or vacuum-nitrogen replacement to ensure dissolved oxygen ≤2ppm; S5: Under clean conditions, the product is aseptically filtered through a 0.22μm filter membrane, filled with nitrogen, and then sealed to obtain the finished product.

[0030] Oxytetracycline was dissolved in a mixed solvent of 2-pyrrolidone, propylene glycol, and water at 45–65 °C, with the initial pH controlled at 5.3–5.8. This allowed the phenolic hydroxyl groups of oxytetracycline to gradually form a stable partially coordinated structure with magnesium ions, while maintaining a weakly acidic solution to prevent degradation into ketone or lactone derivatives. This low-pH coordination at this stage not only reduced precipitation caused by free magnesium ions but also inhibited oxidative yellowing of oxytetracycline during high-temperature dissolution. By controlling the stirring time to 30–60 minutes, sufficient coordination was achieved without crystal nucleation, and the resulting pre-coordinated solution provided a stable feedstock for subsequent ultrafiltration.

[0031] Under nitrogen protection, disodium ethylenediaminetetraacetate and sodium formaldehyde sulfoxylate are added stepwise, with stirring at 55–65°C for 10–30 minutes each. This first chelates residual metal impurities, and then the antioxidant captures free oxygen and peroxides in the solution, forming a stable, weakly reducing environment. Subsequently, the pH is adjusted to 8.2–8.8 with monoethanolamine, which converts the oxytetracycline magnesium complex into a dominant coordination structure, making the solution alkaline to maintain the stability of the tetracyclic structure of oxytetracycline.

[0032] The S4 step introduces the forsythia extract solution, allowing its main active components, forsythoside and phenolic antioxidants, to form weak coordination and hydrogen bond interactions with magnesium ions and oxytetracycline in the system, thereby further stabilizing the active drug molecule and providing anti-inflammatory effects. Dissolved oxygen is controlled below 2 ppm using nitrogen bubbling or vacuum-nitrogen replacement methods to prevent oxidative browning and pH drift of oxytetracycline during storage. The formulation treated in this step shows less color change under long-term accelerated conditions and a significantly higher content retention rate than the untreated sample.

[0033] Finally, aseptic filtration through 0.22μm thoroughly removes particulate matter and bacterial residue, ensuring the sterility and clarity of the finished product. Nitrogen filling and sealing isolate the system from air, effectively extending the antioxidant's effective time and inhibiting oxidation. The final product exhibits stable viscosity, a light yellow and transparent color, and stable storage properties.

[0034] The present invention, by adopting the above technical solution, has the following beneficial effects: (1) This invention optimizes the ratio of 2-pyrrolidone to propylene glycol, enabling the solvent system to remain clear and stable even under high drug concentration conditions. This system achieves a balance between solubility, viscosity, and diffusion rate, effectively preventing crystal precipitation and turbidity formation, while significantly reducing tissue irritation during injection, thus ensuring the long-term clarity and storage stability of the formulation.

[0035] (2) A two-component stabilizing system of disodium ethylenediaminetetraacetate and sodium formaldehyde sulfoxylate was adopted to achieve a dual antioxidant protection mechanism of chelation deactivation and mild reduction. The combination of the two can effectively remove potential metal catalytic factors and free radical sources in the system, significantly inhibit the oxidation and discoloration of the active pharmaceutical ingredient and the generation of impurities, thereby maintaining the color and content stability during long-term storage.

[0036] (3) The pH of the finished product is adjusted within a weakly alkaline range to achieve a balance between solubility, complexation stability and anti-degradation properties. This pH range can prevent precipitation and decomposition under acidic conditions and avoid structural damage caused by a strongly alkaline environment, ensuring that the properties and content of the formulation remain constant during storage and use.

[0037] (4) Forsythia extract is introduced as a natural anti-inflammatory and buffering component, which can reduce adverse irritation at the injection site while maintaining the clarity of the system. Its active ingredient has weak coordination and hydrogen bond interactions with magnesium ions and oxytetracycline, which can enhance the stability of the main drug molecule and play a role in physiological soothing and anti-inflammatory protection, thus achieving a balance between low irritation and stability. Detailed Implementation

[0038] The specific embodiments of the present invention will be described in detail below. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0039] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.

[0040] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0041] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0042] The present invention will now be described in detail with reference to specific embodiments, which are intended to understand rather than limit the invention. Example 1

[0043] This embodiment discloses a highly stable and low-irritation long-acting oxytetracycline injection, the components of which are shown in Table 1 below: Table 1 This embodiment also discloses a method for preparing a highly stable and low-irritation long-acting oxytetracycline injection, comprising the following steps: S1: Add 80 mL of water for injection to the reaction vessel, heat to 50±2℃, add 1.5 g of magnesium chloride and 0.3 g of EDTA-2Na, stir until completely dissolved, and form a clear solution.

[0044] S2: Add 40 mL of 2-pyrrolidone and 30 mL of propylene glycol in sequence, stir well, and then slowly add 20 g of oxytetracycline in batches. Stir at 50℃ and 400 rpm for 40 min to obtain a clear pre-coordinated solution.

[0045] S3: Add 1.5 g of sodium formaldehyde sulfoxylate to the system and maintain stirring for 45 min to ensure the solution is clear.

[0046] S4: Cool to 28°C, adjust the pH to 8.5±0.1 with approximately 0.45 mL of 15% monoethanolamine solution, and add water for injection to a total volume of 100 mL.

[0047] S5: Aseptically filtered through a 0.22 μm filter membrane, filled and sealed under nitrogen protection, and stored away from light. Example 2

[0048] This embodiment discloses a highly stable and low-irritation long-acting oxytetracycline injection, the components of which are shown in Table 2 below: Table 2 This embodiment also discloses a method for preparing a highly stable and low-irritation long-acting oxytetracycline injection, comprising the following steps: S1: Add 80 mL of water for injection to the reactor, maintain the temperature at 50±2℃, add 1.5 g of magnesium chloride and 0.3 g of EDTA-2Na, and stir to dissolve.

[0049] S2: Add 40 mL of 2-pyrrolidone and 40 mL of propylene glycol in sequence, stir well, and then slowly add 30 g of oxytetracycline. Stir at 50℃ and 400 rpm for 40 min until completely dissolved.

[0050] S3: Add 1.5 g of sodium formaldehyde sulfoxylate and stir for 45 min until the solution is clear and transparent.

[0051] S4: Cool to 28°C, add approximately 0.45 mL of 15% monoethanolamine solution, adjust the pH to 8.5±0.1, and add water for injection to a final volume of 100 mL.

[0052] S5: Aseptically filtered through a 0.22 μm terminal, filled with nitrogen, and sealed for storage. Example 3

[0053] This embodiment discloses a highly stable and low-irritation long-acting oxytetracycline injection, the components of which are shown in Table 3 below: Table 3 This embodiment also discloses a method for preparing a highly stable and low-irritation long-acting oxytetracycline injection, comprising the following steps: S1: Take 80 mL of water for injection, heat to 50±2℃, add 1.5 g of magnesium chloride, and stir until completely dissolved.

[0054] S2: Add 40 mL of 2-pyrrolidone and 40 mL of propylene glycol in sequence, stir well, then slowly add 30 g of oxytetracycline, and stir at 50℃ and 400 rpm for 40 min until clear.

[0055] S3: Add 1.5 g of sodium formaldehyde sulfoxylate and stir continuously for 45 min to ensure the solution is clear.

[0056] S4: Cool to 28°C, adjust the pH to 8.5±0.1 with 0.45 mL of 15% monoethanolamine solution, and add water for injection to 100 mL.

[0057] S5: After being filtered through a 0.22 μm terminal filter, it is filled and sealed under nitrogen protection. Example 4

[0058] This embodiment discloses a highly stable and low-irritation long-acting oxytetracycline injection, the components of which are shown in Table 4 below: Table 4 This embodiment also discloses a method for preparing a highly stable and low-irritation long-acting oxytetracycline injection, comprising the following steps: S1: Add 80 mL of water for injection to the reactor, heat to 50±2℃, add 1.5 g of magnesium chloride and 0.3 g of EDTA-2Na in sequence, and stir until completely dissolved.

[0059] S2: Add 40 mL of 2-pyrrolidone and 40 mL of propylene glycol, stir well, and then slowly add 30 g of oxytetracycline in batches. Stir at 50℃ and 400 rpm for 40 min.

[0060] S3: Add 1.5 g of sodium formaldehyde sulfoxylate to the solution and stir for 45 min. The solution should remain clear.

[0061] S4: Cool to 28℃, add about 0.45 mL of 15% monoethanolamine solution, adjust the pH to 8.0±0.1, and add water to 100 mL.

[0062] S5: Filtered through a 0.22 μm terminal filter, filled with nitrogen, and stored away from light. Example 5

[0063] This embodiment discloses a highly stable and low-irritation long-acting oxytetracycline injection solution, as shown in Table 5 below, based on 100 mL: Table 5 This embodiment also discloses a method for preparing a highly stable and low-irritation long-acting oxytetracycline injection, comprising the following steps: S1. Preparation of pre-coordinated solution: 1. Add 35 mL of water for injection to the constant temperature reaction vessel and heat to 55 °C.

[0064] 2. After adding 0.64g of citric acid and stirring to dissolve, add 2.75g of magnesium chloride hexahydrate and stir until completely dissolved.

[0065] 3. Add 38.0 mL of 2-pyrrolidone and 20.0 mL of propylene glycol in sequence, and stir until homogeneous to form a homogeneous mixed solvent.

[0066] 4. Slowly add 25.0g of oxytetracycline in batches, stirring at 400rpm at 55℃ until completely dissolved.

[0067] 5. Adjust the pH to 5.5±0.1 with a trace amount of dilute hydrochloric acid, and maintain stirring for 40 min to obtain a clear pre-coordinated solution.

[0068] S2. Pre-filtration and ultrafiltration: 1. The solution obtained from S1 is pre-filtered through a 0.45μm filter membrane.

[0069] 2. Concentrate using a 20kDa PES ultrafiltration membrane, with the transmembrane pressure difference controlled at 0.20MPa, the operating temperature at 25℃, and the volume concentration factor controlled at 4 times. Discard the permeate and collect the retained solution.

[0070] S3. Complex stabilization and pH establishment of the finished product: 1. Under nitrogen protection, heat the retention solution to 60°C.

[0071] 2. Add 0.30g of disodium ethylenediaminetetraacetate to the solution and stir for 15 minutes.

[0072] 3. Then add 1.50g of sodium formaldehyde sulfoxylate and continue stirring for 15 minutes.

[0073] 4. Cool the system to 28°C, and slowly add about 0.45 mL of 15% monoethanolamine solution until the pH reaches 8.4 ± 0.1.

[0074] S4. Functional excipient addition and deoxidation: 1. Add 0.40g of Forsythia extract (standardized by forsythoside content) to the solution obtained in S3 and stir until completely dissolved.

[0075] 2. Introduce nitrogen gas at a rate of 0.2 L / min and bubble for 15 min to reduce dissolved oxygen to ≤2 ppm.

[0076] 3. Add water for injection to a total volume of 100 mL.

[0077] S5. Terminal aseptic filtration and nitrogen filling: 1. Filter through a 0.22μm terminal filter at 25℃ and discard the first 50mL of filtrate.

[0078] 2. Under nitrogen protection, dispense equal volumes of the clarified filtrate into 10 mL glass ampoules sterilized at 121°C, filling each ampoule with 10 mL.

[0079] 3. Immediately introduce nitrogen gas for filling, seal with flame, and store the finished product away from light.

[0080] Comparative Example 1 This comparative example discloses a long-acting oxytetracycline injection, the components of which are shown in Table 6 below per 100 mL: Table 6 This comparative example also discloses a method for preparing a long-acting oxytetracycline injection, comprising the following steps: S1: Add 35 mL of water for injection to the reactor, heat to 55°C, add 0.64 g of citric acid and stir to dissolve.

[0081] S2: Add 38 mL of 2-pyrrolidone and 20 mL of propylene glycol in sequence, stir well, then slowly add 25 g of oxytetracycline, and stir at 55℃ for 40 min until dissolved.

[0082] S3: Under nitrogen protection, add 0.30 g of EDTA-2Na and stir for 15 min, then add 1.50 g of sodium formaldehyde sulfoxylate and stir for 15 min.

[0083] S4: Cool to 28℃, add 0.45 mL of 15% monoethanolamine solution to adjust the pH to 8.4±0.1, add water to 100 mL, then add 0.40 g of Forsythia extract and stir well.

[0084] S5: Filled after filtration through a 0.22 μm filter membrane.

[0085] Comparative Example 2 This comparative example discloses a long-acting oxytetracycline injection, the components of which are shown in Table 7 below per 100 mL: Table 7 This comparative example also discloses a method for preparing a long-acting oxytetracycline injection, comprising the following steps: S1: Add 35 mL of water for injection to the reactor, heat to 55°C, add 0.64 g of citric acid and 2.75 g of magnesium chloride hexahydrate, and stir to dissolve.

[0086] S2: Add 38 mL of 2-pyrrolidone and 20 mL of propylene glycol, stir well, then add 25 g of oxytetracycline in batches, and stir at 55℃ for 40 min until clear.

[0087] S3: Cool to 28℃, and slowly add 0.45 mL of 15% monoethanolamine solution to adjust the pH to 8.4±0.1.

[0088] S4: Add 0.40 g of Forsythia extract and stir well, then add water to 100 mL.

[0089] S5: Filled and sealed after being filtered through a 0.22 μm terminal filter.

[0090] Comparative Example 3 This comparative example discloses a long-acting oxytetracycline injection, the components of which are shown in Table 8 below per 100 mL: Table 8 This comparative example also discloses a method for preparing a long-acting oxytetracycline injection, comprising the following steps: S1: Add 35 mL of water for injection to the reactor, heat to 55°C, add 0.64 g of citric acid and 2.75 g of magnesium chloride hexahydrate, and stir to dissolve.

[0091] S2: Add 38 mL of 2-pyrrolidone and 20 mL of propylene glycol, stir well, then add 25 g of oxytetracycline and stir at 55℃ for 40 min.

[0092] S3: Under nitrogen protection, add 0.30 g of EDTA-2Na and stir for 15 min, then add 1.50 g of sodium formaldehyde sulfoxylate and stir for 15 min.

[0093] S4: Cool to 28℃, slowly add 0.45 mL of 15% monoethanolamine solution, adjust the pH to 8.4±0.1, and add water to 100 mL.

[0094] S5: Filtered through a 0.22 μm terminal filter, then filled and sealed.

[0095] Performance testing 1. Appearance and clarity Visually inspect the appearance against a white background with black lettering; record the color description under an 8000 lx standard light source. Samples were taken using 1 cm quartz cuvettes, and the A350 was measured. The rate of change of A350 was used to characterize the early browning trend.

[0096] 2. Particulate control Subvisible particles according to USP <788> For injection preparations (light obscuration method), count the number of particles ≥10μm (particles / mL). Visible foreign matter should be examined according to the first method of "Visible Foreign Matter Examination" in General Chapter 0904 of the 2020 edition of the Chinese Pharmacopoeia, Part IV. In a dark room, place the test sample at the edge of a light-shielding plate, and gently rotate and invert the container at a clear viewing distance to suspend any visible foreign matter in the solution. Visual inspection should then be performed against both a non-reflective black background and a non-reflective white background.

[0097] 3. pH drift Calibrate the glass electrode (pH 4.00 / 7.00 / 10.01) and measure at 25℃; record the initial pH and the pH at each time point.

[0098] 4. Viscosity and Rheology At 25℃, use a rotational rheometer (circular plate or concentric cylinder) with a shear rate of 10-100 s. -1 Step-by-step scanning; power-law model τ=K·γ n By fitting the data, the apparent viscosity η and the rheological index n are obtained.

[0099] 5. Stability Design Acceleration: 40℃ / RH75% (protected from light), sampling at 0, 5, and 10 days; Long-term: 25℃ / RH 60-75% (protected from light), sampling at 0, 1, 3, and 6 months. Complete items 1-5 and DO records at each point.

[0100] 6. Stimulation Model New Zealand white rabbits were injected intramuscularly with 0.5 mL into the quadriceps femoris muscle at a single point. Redness, swelling, and induration were scored in a blinded manner at 24 / 48 / 72 hours post-administration (0-4 points / item), with the highest score recorded as the score at that time point. The exudate level (0-3) was also recorded. This data is for relative comparison between prescriptions only.

[0101] The test results are shown in Table 9-12.

[0102] Table 9. Accelerated stability test results (40 °C / RH 75%, 10 d) Table 10. Long-term stability (25 ℃ / RH 75%, 6 months) test results Table 11 Table 12 Examples 1-5 maintained low ΔA350, low particulate matter, minimal ΔpH, and high content under both accelerated and long-term conditions, with Example 5 being the best; Comparative Examples 1-3 showed increased color, increased particulate matter, and significant pH shift.

[0103] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A highly stable, low-irritation, long-acting oxytetracycline injection, characterized in that, Per 100 mL of formulation, it includes the following components: 20-35g of oxytetracycline; 30-45 mL of 2-pyrrolidone; 15-25 mL of propylene glycol; Disodium ethylenediaminetetraacetate 0.10–0.50 g; Sodium formaldehyde sulfoxylate 1.0–2.0 g; Magnesium salts or magnesium oxide according to Mg 2+ 0.15 to 0.35 equivalents of oxytetracycline molar amount; Forsythia extract 0.20-0.60g, wherein the forsythia extract contains 2-8mg / 100mL based on the content of forsythoside; The injection solution contains a pH adjuster, which is used to control the pH of the finished product at 8.2 to 8.8; The remaining volume is made up to 100 mL with water for injection; The formulation is sterile filtered through a 0.22μm terminal filter, and the dissolved oxygen level is ≤2ppm before filling.

2. The highly stable, low-irritation long-acting oxytetracycline injection according to claim 1, characterized in that, The water-soluble solvent system of the injection solution is composed of 2-pyrrolidone, propylene glycol and water, wherein the volume ratio of 2-pyrrolidone to propylene glycol is 1.4 to 2.5:1, and 2-pyrrolidone accounts for 30% to 44% of the total volume of the water-soluble solvent system, and propylene glycol accounts for 16% to 24% of the total volume of the water-soluble solvent system.

3. The highly stable, low-irritation long-acting oxytetracycline injection according to claim 1, characterized in that, The mass ratio of disodium ethylenediaminetetraacetate to sodium formaldehyde sulfoxylate is 1:6 to 12, and the order in which they are added during the preparation process is specified as follows: disodium ethylenediaminetetraacetate is added first, followed by sodium formaldehyde sulfoxylate.

4. The highly stable, low-irritation long-acting oxytetracycline injection according to claim 1, characterized in that, Magnesium salts are selected from one or two of magnesium chloride, magnesium acetate, or magnesium oxide.

5. The highly stable, low-irritation long-acting oxytetracycline injection according to claim 1, characterized in that, The injection solution also contains an organic acid stabilizer, which is selected from one or two of citric acid, malic acid, and tartaric acid, with a total concentration of 0.05–0.25 mol / L based on the acid radical; the organic acid reacts with Mg... 2+ The molar ratio of feed ingredients is 0.3–1.2:1, with oxytetracycline and Mg... 2+ The molar ratio of feed is 2.9 to 6.6:

1.

6. The highly stable, low-irritation long-acting oxytetracycline injection according to claim 1, characterized in that, The pH adjuster is a monoethanolamine solution with a mass fraction of 10% to 20%.

7. The highly stable, low-irritation long-acting oxytetracycline injection according to claim 1, characterized in that, The pH adjuster is a mixture of monoethanolamine and N-methyldiethanolamine, and the injection solution also contains lactose monohydrate. The mass ratio of N-methyldiethanolamine to lactose monohydrate is 3–8:1, and the two together account for 0.30–1.20 wt% of the total mass of the injection solution. N-methyldiethanolamine accounts for 30 to 60 wt% of the total mass of the pH adjuster.

8. The highly stable, low-irritation long-acting oxytetracycline injection according to claim 1, characterized in that, At 25 °C, the apparent viscosity of the injection solution is 15–25 mPa·s, and at a shear rate of 10–100 s⁻¹, it is [missing value]. -1 Within the interval, it conforms to the power-law rheological model, with the rheological index n ranging from 0.60 to 0.

90.

9. A method for preparing a highly stable, low-irritation long-acting oxytetracycline injection according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1: Dissolve oxytetracycline in a mixed solvent of 2-pyrrolidone, propylene glycol and water for injection at 45-65℃, add a magnesium source and adjust the pH of the solution to 5.3-5.8 with acid, and stir for 30-60 min to form a pre-coordinated solution; S2: The solution obtained in step S1 is sequentially pre-filtered with 0.45 μm and treated with an ultrafiltration membrane with a molecular weight cutoff of 10-30 kDa, with a transmembrane pressure of 0.10-0.30 MPa, a temperature of 20-30 °C, and a volume concentration factor of 2-6 times. The permeate is discarded and the retained solution is collected. S3: Under nitrogen protection, add disodium ethylenediaminetetraacetate to the retention solution and stir at 55-65°C for 10-30 min; then add sodium formaldehyde sulfoxylate and stir for 10-30 min; adjust the pH to 8.2-8.8 with monoethanolamine. S4: Add the Forsythia extract solution that meets the criteria of claim 5 to the solution obtained in step S3 and stir until homogeneous; use nitrogen bubbling or vacuum-nitrogen replacement to ensure dissolved oxygen ≤2ppm; SS5: Under clean conditions, the product is aseptically filtered through a 0.22μm filter membrane, filled with nitrogen, and then sealed to obtain the finished product.

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