A method for detecting related substances of lidocaine gel patch

Abstract

The application discloses a detection method of lidocaine gel plaster related substances and application thereof, and belongs to the technical field of drug analysis. The method is aimed at lidocaine gel plaster containing lidocaine, urea, hydroxybenzyl and / or hydroxybenzyl propyl, a sample is subjected to ultrasonic extraction by methanol to obtain a test solution, a Waters Xterra RP18 chromatographic column is used, a potassium dihydrogen phosphate solution with pH 9-10 is used as mobile phase A, acetonitrile is used as mobile phase B, gradient elution is carried out under a detection wavelength of 230 nm, and impurity A, impurity B and other related substances are subjected to qualitative or quantitative determination. The method can avoid the use of ion pair reagents, improve the peak shape of impurity B, and realize good separation of impurity A, impurity B, impurity H, a lidocaine main peak and an excipient peak, and is suitable for quality control, stability investigation and registration inspection of the specific lidocaine gel plaster matrix.

Description

Technical Field

[0001] This invention belongs to the field of pharmaceutical analysis technology, specifically relating to a method for detecting related substances in lidocaine gel patches. Background Technology

[0002] Lidocaine gel patches are topical preparations made by mixing the active ingredient lidocaine with a hydrophilic polymer gel matrix and coating it onto a backing material. They can be used to relieve postherpetic neuralgia. These patches contain drugs, gel matrix, penetration enhancers, preservatives, and other excipients. The sample matrix is ​​complex, and multiple related substances may be generated or introduced during production and storage.

[0003] Lidocaine raw material has been included in the pharmacopoeias of many countries, but lidocaine gel patch as a preparation has not yet had a unified method for detecting related substances in some pharmacopoeias.

[0004] Lidocaine Cataplasms, manufactured by TEIKOKU SEIYAKU, Co., Ltd. (Japan). Product specifications: Each patch (14cm x 10cm) contains 14g of ointment, with 700mg of lidocaine; Indications: For the relief of postherpetic neuralgia, on unbroken skin.

[0005] Based on the research on the raw materials of this product and the existing formulations on the market, the substances that require special attention in lidocaine gel patches include impurities A, B, and H.

[0006] Table 1. Correspondence between related substances of lidocaine

[0007] Impurity A 2,6-Dimethylaniline Impurity A Impurity A 2,6-Dimethylaniline Impurity B / / / DEAMMQ impurity H / impurity H impurity H /

[0008] Existing methods for detecting lidocaine related substances mainly include methods for raw materials and methods for imported drug registration standards (patch preparations).

[0009] The active pharmaceutical ingredient (API) process typically employs a pH 8.0 phosphate buffer-acetonitrile system. This system provides good peak shape for the main peak and some impurity peaks, but the separation between impurities A, B, and H is insufficient, especially for impurities B and H, which are difficult to separate at the baseline.

[0010] The standard method for imported drug registration (patch formulation) uses an ion-pairing reagent system containing sodium dodecyl sulfate. This system can be used for the detection of specific items, but ion-pairing reagents have problems such as long system equilibration time, complex mobile phase preparation and maintenance, and poor compatibility and durability with chromatographic columns, which are not conducive to the routine quality control of related substances in lidocaine gel patches.

[0011] Table 2 Comparison of analytical methods for lidocaine related substances

[0012] method High performance liquid chromatography High performance liquid chromatography High performance liquid chromatography chromatographic column Octadecylsilane-bonded silica gel was used as the packing material (Waters Xterra RP18, 3.9 mm × 150 mm, 5 μm or equivalent column). Octadecylsilane-bonded silica gel was used as a filler. Octadecylsilane-bonded silica gel was used as the packing material (TSKgel ODS-120T, 150mm × 4.6mm, 5μm or equivalent column). mobile phase Potassium dihydrogen phosphate solution (4.85g potassium dihydrogen phosphate dissolved in 1000ml water, pH adjusted to 8.0 with saturated sodium hydroxide) - acetonitrile (70:30) Phosphate buffer (1.3 ml of 1 mol / L sodium dihydrogen phosphate solution and 32.5 ml of 0.5 mol / L disodium hydrogen phosphate solution, diluted with water to 1000 ml, and shaken well) - acetonitrile (50:50) (adjust pH to 8.0 with phosphate) Sodium dodecyl sulfate solution (dissolve 5g of sodium dodecyl sulfate and 1.0ml of phosphoric acid in 600ml of water) - acetonitrile (60:40) Washing method Isocratic elution Isocratic elution Isocratic elution solvent mobile phase mobile phase methanol Column temperature 30℃ N / A 40℃ Flow rate 1.0 ml / min N / A Adjust the flow rate so that the retention time of the 2,6-dimethylaniline peak is approximately 12 minutes. Detection wavelength 230nm 230nm 228nm Injection volume 20μl 20μl 10μl runtime Record the chromatogram up to 3.5 times the retention time of the main component peak. N / A N / A System suitability solution N / A Take an appropriate amount of 2,6-dimethylaniline reference standard and lidocaine hydrochloride, dissolve and dilute them in the mobile phase to prepare a mixed solution containing approximately 50 μg of each in 1 ml. Take appropriate amounts of 2,6-dimethylaniline reference standard and lidocaine hydrochloride reference standard, dissolve them in methanol, and dilute to prepare a mixed solution containing approximately 40 μg of each in 1 ml. Sensitivity solution N / A N / A Accurately weigh an appropriate amount of lidocaine reference standard, dissolve it in methanol, and quantitatively dilute it to prepare a solution containing approximately 0.15 µg per ml. Reference solution Accurately weigh appropriate amounts of lidocaine impurity A and lidocaine impurity H reference standards, dissolve and quantitatively dilute them in the mobile phase to prepare a mixed solution containing 0.5 μg of impurity A and 0.15 μg of impurity H per 1 ml. Accurately weigh an appropriate amount of 2,6-dimethylaniline reference standard, dissolve and dilute it in the mobile phase to prepare a solution containing approximately 0.5 μg per ml. Accurately weigh appropriate amounts of 2,6-dimethylaniline (impurity A) reference standard and lidocaine reference standard, dissolve them in methanol, and quantitatively dilute to prepare a mixed solution containing 0.25 μg of impurity A and 0.48 μg of lidocaine per 1 ml. Test solution Accurately weigh this product, dissolve it in the mobile phase, and quantitatively dilute it to prepare a solution containing 5 mg of lidocaine per ml. Take an appropriate amount of this product, dissolve it in the mobile phase, and dilute quantitatively to prepare a solution containing approximately 5 mg per ml. Take one dose of this product, accurately weigh it, cut it into 4cm × 5cm pieces, accurately weigh and cut into small fragments, transfer all to a 100ml reflux flask, add 50ml methanol, heat in a 75℃ water bath under reflux for 1 hour, let it cool to room temperature, and transfer the extract to a 200ml volumetric flask. Repeat the operation twice, starting from "add 50ml methanol", combine the extracts, dilute to the mark with methanol, and shake well. System applicability requirements The resolution between lidocaine impurity A and lidocaine impurity H in the reference solution should be greater than 1.5. In the system suitability solution chromatogram, the resolution between the 2,6-dimethylaniline peak and the lidocaine peak should meet the requirements. In the system suitability solution chromatogram, the resolution between the peaks of 2,6-dimethylaniline and lidocaine should be no less than 2.0. In the sensitivity solution chromatogram, the signal-to-noise ratio of the peak height of the main component should be greater than 10. Impurity Quantification Methods External standard method for impurities + self-comparison method External standard method for impurities Impurity external standard method + principal component external standard method Limitation requirements If the chromatogram of the test solution contains a chromatographic peak with the same retention time as impurity A, the peak area calculated using the external standard method shall not exceed 0.01%. If the chromatographic peak with the same retention time as impurity H, the peak area calculated using the external standard method shall not exceed 0.003%. The area of ​​any other single impurity peak shall not exceed the area of ​​the main peak of the control solution (0.10%), and the sum of the areas of all impurity peaks shall not exceed 5 times (0.5%) the area of ​​the main peak of the control solution. If the chromatogram of the test solution contains a peak with the same retention time as 2,6-dimethylaniline, the peak area calculated using the external standard method shall not exceed 0.01%. If impurity peaks are present in the chromatogram of the test solution, calculated by peak area using the external standard method, the content of 2,6-dimethylaniline (impurity A) shall not exceed 0.04% of the lidocaine label; calculated by peak area using the main component external standard method, the content of DEAMMQ (impurity B, relative retention time of approximately 0.92 times the main peak, multiplied by a correction factor of 0.142) shall not exceed 0.1% of the lidocaine label, other individual impurities shall not exceed 0.10% of the lidocaine label, and the total impurities shall not exceed 0.5% of the lidocaine label. Peaks in the chromatogram of the test solution with an area smaller than the main peak area of ​​the sensitivity solution are negligible (0.03%). Summary of the Invention

[0013] The technical problem to be solved by the present invention is to provide a method for detecting related substances in lidocaine gel patches containing lidocaine, urea, methylparaben and / or propylparaben, so as to solve the problems of insufficient separation of impurities A, B and H, peak tailing of impurity B, complex operation of ion-pairing reagent system and cumbersome sample processing steps in the existing methods, and to make the method stable in the specific formulation matrix.

[0014] To address the aforementioned technical problems, this invention provides a method for detecting related substances in lidocaine gel patches and its application. The method employs high-performance liquid chromatography (HPLC) for gel patch matrices containing lidocaine, urea, and methylparaben and / or propylparaben. The detection method of this invention is as follows:

[0015] A Waters Xterra RP18 column was used with phosphate buffer (pH 9-10) as mobile phase A and acetonitrile as mobile phase B. Gradient elution was performed at a detection wavelength of 230 nm, and the test solution was prepared by ultrasonic extraction with methanol.

[0016] Preferably, the chromatographic column is a Waters Xterra RP18 column with dimensions of 4.6 mm x 250 mm and a packing particle size of 5 μm. This column employs a packing material design that embeds polar groups within the C18 long chain, which can reduce the silanol effect and improve the peak shape of basic compounds, especially impurity B.

[0017] In a preferred embodiment, mobile phase A is a potassium dihydrogen phosphate solution, specifically 4.85 g of potassium dihydrogen phosphate is dissolved in water and diluted to 1000 ml, and the pH is adjusted to 9.5 with saturated sodium hydroxide solution; mobile phase B is acetonitrile.

[0018] Preferably, a phosphate buffer solution with pH 9-10 is used as mobile phase A; more preferably, a phosphate buffer solution with pH 9.5 is used as mobile phase A.

[0019] Preferably, the gradient elution program is as follows: 0-10 min, mobile phase A is 60-70%, mobile phase B is 30-40%; 10-20 min, mobile phase A decreases from 60-70% to 35-45%, mobile phase B increases from 30-40% to 55-65%; 20-30 min, mobile phase A is 35-45%, mobile phase B is 55-65%; 30-31 min, mobile phase A increases from 35-45% to 60-70%, mobile phase B decreases from 55-65% to 30-40%; 31-40 min, mobile phase A is 60-70%, mobile phase B is 30-40%.

[0020] More preferably, the gradient elution program is as follows: 0-10 min, mobile phase A is 65% and mobile phase B is 35%; 10-20 min, mobile phase A decreases from 65% to 40% and mobile phase B increases from 35% to 60%; 20-30 min, mobile phase A is 40% and mobile phase B is 60%; 30-31 min, mobile phase A is 65% and mobile phase B decreases from 60% to 35%; 31-40 min, mobile phase A is 65% and mobile phase B is 35%.

[0021] Preferably, the column temperature is 40℃, the flow rate is 1.0 ml / min, the injection volume is 10 μl, and the detection wavelength is 230 nm.

[0022] Preferably, the test solution is prepared as follows: Take one lidocaine gel patch, weigh it and cut it into small pieces, transfer it all to a 150 ml Erlenmeyer flask, add 80 ml of methanol to completely submerge the sample, sonicate for 60 min, and transfer the extract to a 250 ml volumetric flask; repeat the operation twice starting from "add 80 ml of methanol", combine the extracts, dilute with methanol to the mark, and shake well.

[0023] Preferably, the reference solution is prepared as follows: an appropriate amount of impurity A reference standard is accurately weighed, dissolved and diluted with methanol to obtain impurity A stock solution; impurity B reference standard, lidocaine reference standard and impurity A stock solution are dissolved and diluted with methanol to obtain the reference standard stock solution; then the reference standard stock solution is accurately measured and diluted with methanol to obtain the reference solution.

[0024] A method for detecting related substances in lidocaine gel patches, wherein the method employs high-performance liquid chromatography (HPLC), and the chromatographic conditions are as described in Table 3:

[0025] Table 3. Analytical methods for related substances in lidocaine gel patches.

[0026] Mobile phase A Potassium dihydrogen phosphate solution (pH 9.5) Mobile phase B Acetonitrile Detection wavelength 230nm Flow rate 1ml / min Column temperature 40℃ Injection volume 10μl Washing process See Table 4 solvent methanol Reference solution Accurately weigh approximately 22.4 mg of impurity A reference standard, place it in a 20 ml volumetric flask, dissolve and dilute to the mark with methanol, and mix well to prepare the impurity A stock solution. Accurately weigh approximately 14 mg of impurity B reference standard and approximately 14 mg of lidocaine reference standard, place them in the same 50 ml volumetric flask, accurately measure 5 ml of the above impurity A stock solution, add it to the volumetric flask, dissolve and dilute to the mark with methanol, and mix well to prepare the reference standard stock solution. Accurately measure 1 ml of the reference standard stock solution, place it in a 100 ml volumetric flask, dilute to the mark with methanol, and mix well to prepare the reference standard solution. Test solution Take one patch of this product, weigh it, and cut it into small pieces. Transfer the entire sample to a 150ml Erlenmeyer flask, add 80ml of methanol to completely submerge the sample, sonicate for 60 minutes, and transfer the extract to a 250ml volumetric flask. Repeat the operation twice, starting from "add 80ml of methanol". Combine the extracts, dilute with methanol to the mark, and shake well. Blank excipient solution Take one blank plaster, cut it into small pieces, and transfer it all to a 150ml Erlenmeyer flask. Add 80ml of methanol to completely submerge the sample, sonicate for 60 minutes, and transfer the extract to a 250ml volumetric flask. Repeat the operation twice, starting from "add 80ml of methanol". Combine the extracts, dilute with methanol to the mark, and shake well. System applicability requirements In the chromatogram of the reference solution, the resolution of impurity A, impurity B and the main peak meets the requirements. Limitation requirements If impurity peaks are present in the chromatogram of the test solution, the peak area calculated using the external standard method shall be such that the content of impurity A shall not exceed 0.04% of the labeled amount of lidocaine; the peak area calculated using the external standard method for impurity B shall not exceed 0.1% of the labeled amount of lidocaine; and the peak area calculated using the external standard method for the main component shall be such that the content of any other single impurity shall not exceed 0.10% of the labeled amount of lidocaine, and the total impurities shall not exceed 0.5% of the labeled amount of lidocaine.

[0027] Table 4 Gradient elution conditions

[0028] 0 65 35 10 65 35 20 40 60 30 40 60 31 65 35 40 65 35

[0029] It should be noted that impurity H was investigated as a challenge impurity during the method development phase, examining its location and separation from other peaks. However, based on the analysis, it was found that impurities A and B are degradation impurities in the formulation product, meaning they will gradually degrade and be generated in the lidocaine gel patch. From a product safety perspective, impurities A and B need to be thoroughly studied and incorporated into quality standards for strict control. Impurity H, on the other hand, is a process impurity, a byproduct of the active pharmaceutical ingredient (API) synthesis process. It has been reasonably controlled in the API and will not degrade and be generated in the lidocaine gel patch. Therefore, in the final method established in this invention, it is not necessary to strictly control impurity H as a known impurity; instead, it should be controlled according to the limits for other individual impurities.

[0030] The related substance detection method of this invention targets lidocaine gel patches manufactured by TEIKOKUSEIYAKU, Co., Ltd. and its generic drugs. According to China's "Drug Registration Management Measures" and related supporting documents, generic drugs refer to drugs that imitate marketed original drugs, achieving the same level of quality and efficacy as the imitated original drugs.

[0031] To establish a method for detecting related substances in the complex matrix of lidocaine gel patches, the inventors of this patent have conducted systematic and continuous exploration on several key issues, including detection sensitivity, separation of key impurities, interference from excipients, peak shape of impurity B, pH durability of the mobile phase, and elution of strongly retained components.

[0032] Initially, the method based on the EP-12.3 / USP-2026 standard was attempted. However, it was found that the separation between impurities A, B, and H was insufficient under this method. Subsequently, the inventors tried replacing the original buffer system with a 0.1% perchloric acid system in an attempt to simplify the method and improve its robustness. At this point, a new problem arose: the response of impurity A decreased significantly under acidic conditions, failing to meet the sensitivity requirements, and the exploration failed.

[0033] The inventors then returned to the pH 8.0 phosphate system and investigated the effects of gradient elution, different chromatographic columns, organic phase ratios, tailing agents, mobile phase pH, and column temperature on resolution and peak shape. Through numerous experiments, the inventors gradually discovered that conventional methods such as adjusting the elution program, adding triethylamine, or increasing the pH could not solve the problems of impurity B tailing and the separation of key components.

[0034] The inventors further explored the chromatographic column. They unexpectedly discovered that using a Waters Xterra RP18 column (4.6 mm × 250 mm, 5 μm) with specially packed material significantly improved the peak shape of impurity B, while the mobile phase A at pH 9.5 significantly improved the separation stability between the impurity and excipient peaks.

[0035] To further improve the experimental results, the inventors introduced gradient elution on the basis of the already effective separation, which further improved the shape of the late elution peak and ensured the effective elution of the strongly retained components in the blank excipient.

[0036] The above series of explorations show that the final method is not obtained by simple parameter optimization, but is a comprehensive solution formed on the basis of multiple attempts, eliminations and verifications, which fully reflects the systematic efforts made by researchers to solve the problem of accurate detection of related substances in the complex matrix of plaster.

[0037] The detection target of this invention is related substances in lidocaine gel patches. The applicability of the method is evaluated based on the defined formulation matrix, rather than on limiting the specific manufacturers, sources or preparation processes of each raw material and excipient.

[0038] To address the potential differences in background impurity spectra caused by raw materials and excipients from different sources, this invention employs comparative experiments using blank excipient solutions, blank solvents, and spiked test solutions to examine whether impurity A, impurity B, hydroxylidocaine, and the lidocaine main peak are interfered with by matrix peaks or other impurity peaks. The results show that within the lidocaine gel patch formulation matrix defined in this invention, each target peak has satisfactory separation from adjacent peaks, and the target impurities can be identified and quantified.

[0039] For other unknown impurity peaks that have been separated and can be integrated, quantification can be performed using the external standard method of principal component analysis, and evaluation can be conducted according to the limits for individual impurities and total impurities. The external standard method of principal component analysis and total impurity control are used for the quantification and quality determination of other impurities, while the conclusion that the target impurity is not affected by co-elution should be based on the results of specificity and resolution tests.

[0040] For the formulation system defined in this invention, as long as the finished product sample has a representative analytical matrix composed of lidocaine, urea, and methylparaben and / or propylparaben, and is prepared, chromatographically separated and quantified according to the test sample preparation, chromatographic separation and quantification conditions disclosed in this specification, those skilled in the art can complete the method of this invention.

[0041] Compared with the prior art, the present invention has at least the following beneficial effects:

[0042] 1. This invention uses a phosphate buffer-acetonitrile system with pH 9.5, which avoids the use of long-chain alkyl ions such as sodium dodecyl sulfate as reagents. The mobile phase preparation is simpler, the system equilibrates faster, the baseline is more stable, and the damage to the chromatographic column is less.

[0043] 2. This invention combines an octadecylsilane-bonded silica column with embedded polar groups with a pH 9.5 phosphate system, which can significantly improve the tailing problem of impurity B and achieve good separation between impurity A, impurity B, impurity H, lidocaine main peak and blank excipient peak.

[0044] 3. This invention improves the proportion of organic phase before impurity B and lidocaine peaks by setting a gradient elution program, thereby improving the peak shape of impurity B and the main peak, and promoting the elution of strongly retained excipients or unknown components, thus improving the specificity and accuracy of the method.

[0045] 4. This invention uses ultrasonic extraction with methanol instead of heating and reflux extraction, which simplifies sample pretreatment. Compared with heating and reflux, the lidocaine content determination results are not significantly different, making it suitable for standardizing the sample treatment methods in related substances, content determination, and content uniformity checks.

[0046] 5. The method of the present invention can be used for quality control of impurities A, impurities B and other related substances in the above-mentioned specific lidocaine gel patch matrix, and is suitable for production release, stability study and drug registration testing. Attached Figure Description

[0047] Figure 1 UV full-wavelength scan of impurity A (pH 8.0 buffer system)

[0048] Figure 2 UV full-wavelength scan of impurity B (pH 8.0 buffer system)

[0049] Figure 3 UV full-wavelength scan of impurity H (pH 8.0 buffer system)

[0050] Figure 4 Lidocaine UV full-wavelength scan (pH 8.0 buffer system)

[0051] Figure 5 Impurity localization chart for related substances methods in EP-12.3 / USP-2026 standard

[0052] Figure 6 UV full-wavelength scan of impurity A (0.1% perchloric acid system)

[0053] Figure 7 Chromatographic condition optimization ① Impurity localization map

[0054] Figure 8 Chromatographic condition optimization ② Impurity localization map (elution program 1)

[0055] Figure 9 Optimization of chromatographic conditions ② Impurity localization map (elution program 2)

[0056] Figure 10 (Chromatographic condition optimization ③ Impurity localization map)

[0057] Figure 11. Chromatographic condition optimization ④. Localization map of impurity B (triethylamine at different concentrations).

[0058] Figure 12 Chromatographic condition optimization ④-2 Impurity B localization map (different mobile phase pH values)

[0059] Figure 13 Chromatographic condition optimization ④-3 Impurity B localization map (different elution programs)

[0060] Figure 14 Chromatographic condition optimization ⑤ Impurity localization map (30℃)

[0061] Figure 15 Chromatographic condition optimization ⑤ Impurity localization map (40℃)

[0062] Figure 16 Chromatographic condition optimization ⑤ Impurity localization map (45℃)

[0063] Figure 17 Optimization of chromatographic conditions ⑥ Typical spectra of related substances (pH 8.0)

[0064] Figure 18 Optimization of chromatographic conditions ⑥ Typical spectra of related substances (pH 7.8)

[0065] Figure 19 Optimization of chromatographic conditions ⑥ Typical chromatograms of related substances (pH 8.2)

[0066] Figure 20 Optimization of chromatographic conditions ⑦ Typical spectra of related substances (pH 9.0)

[0067] Figure 21 Optimization of chromatographic conditions ⑦ Typical spectra of relevant substances (pH 9.5)

[0068] Figure 22 Optimization of chromatographic conditions ⑦ Typical chromatograms of related substances (pH 10.0)

[0069] Figure 23 Optimization of chromatographic conditions ⑧ Typical spectra of related substances (pH 9.5)

[0070] Figure 24 Exclusive overlay image

[0071] Figure 25 Lidocaine linear relationship diagram

[0072] Figure 26 Linear relationship diagram of impurity A

[0073] Figure 27 Linear relationship diagram of impurity B

[0074] Figure 28 Linear relationship of impurity H Detailed Implementation

[0075] The present invention will be further described below with reference to embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Equivalent adjustments made by those skilled in the art to the chromatographic conditions and sample processing conditions disclosed in this specification without departing from the concept of the present invention should fall within the scope of protection of the present invention; however, the application of the present invention is still limited to the lidocaine gel patch matrix system defined in this specification.

[0076] In the embodiments of this patent, the test sample used is lidocaine gel patch (Lidocaine Cataplasms); this drug is marketed as Lidoderm in China, and as Versatis in Europe, Russia, and other countries. The manufacturer is TEIKOKUSEIYAKU, Co. Ltd. (Japan). Product specifications: each patch (14cm × 10cm) contains 14g of patch and 700mg of lidocaine. However, the method of this patent is applicable to various lidocaine gel patches, including but not limited to the products listed in Table 5 below:

[0077] Table 5

[0078] 1 Lidocaine Gel Patch Lidoderm Each patch (14.0cm x 10.0cm) contains 14g of ointment and 700mg of lidocaine. TEIKOKU SEIYAKU,Co. Ltd 2 Lidocaine Gel Patch / Each patch (14.0cm x 10.0cm) contains 14g of ointment and 700mg of lidocaine. Shaanxi Dongke Pharmaceutical Co., Ltd. 3 Lidocaine Gel Patch Jiudian Each patch (14.0cm x 10.0cm) contains 14g of ointment and 700mg of lidocaine. Hunan Jiudian Pharmaceutical Co., Ltd. 4 Lidocaine Gel Patch Fu Erkang Each patch (14.0cm x 10.0cm) contains 14g of ointment and 700mg of lidocaine. Hainan Huiyuantang Pharmaceutical Co., Ltd. 5 Lidocaine Gel Patch Debenone Each patch (14.0cm x 10.0cm) contains 14g of ointment and 700mg of lidocaine. Beijing Taide Pharmaceutical Co., Ltd.

[0079] Indications: For the relief of postherpetic neuralgia, on unbroken skin.

[0080] In the embodiments of this patent, the method for synthesizing lidocaine active pharmaceutical ingredient is a conventional process, such as the method disclosed in US 2441498; and the conventional process mentioned in the background art of CN110938012A: using glacial acetic acid as a solvent and sodium acetate as an alkaline catalyst, 2,6-dimethylaniline is acylated with chloroacetyl chloride to obtain the intermediate chloroacetyl-2,6-dimethylaniline. Then, using toluene as a solvent, the intermediate chloroacetyl-2,6-dimethylaniline is refluxed with diethylamine to carry out the N-alkylation reaction to generate lidocaine.

[0081] The reference standards for impurities A, B, and H in this patent were purchased from the following sources:

[0082] Table 6 Information on Impurity Reference Standards

[0083] Impurity A 87-62-7 QUALITY CONTROL CHEMICALS INC. Impurity B N / A QUALITY CONTROL CHEMICALS INC. impurity H 1131-01-7 SINCO PHARMACHEM INC.

[0084] Example 1: Reproduction of the related substances method for gel patches using EP-12.3 / USP-2026 standards

[0085] Solutions for impurities A, B, and H, as well as a solution of lidocaine gel patch, were prepared separately to reproduce the related substances detection method in EP-12.3 / USP-2026. A diode array detector was used to perform a full-wavelength scan of lidocaine and each impurity in the wavelength range of 190 nm to 400 nm. The results are as follows:

[0086] Table 7 Reproducibility results of the related substances method in EP-12.3 / USP-2026 standard

[0087] Mobile phase A Potassium dihydrogen phosphate solution (pH 8.0) Mobile phase B Acetonitrile Detection wavelength 230nm Flow rate 1ml / min Column temperature 30℃ Injection volume 10μl runtime 30min Washing process Mobile phase A:Mobile phase B = 70:30

[0088] Experimental results:

[0089] The UV full-wavelength scan of impurity A (pH 8.0 buffer system) is shown below. Figure 1 The UV full-wavelength scan of impurity B (pH 8.0 buffer system) is shown below. Figure 2 The full-wavelength UV scan of impurity H (pH 8.0 buffer system) is shown below. Figure 3 The full-wavelength UV scan of lidocaine (pH 8.0 buffer system) is shown below. Figure 4 The impurity localization chart for the related substances method in EP-12.3 / USP-2026 standard is available in [link to relevant substances method]. Figure 5 .

[0090] in conclusion:

[0091] (1) According to the results of ultraviolet full-wavelength scanning, impurity A, impurity B, impurity H and lidocaine have the maximum absorption wavelength at 230nm. Based on the lidocaine EP-12.3 / USP-2026 standard and the pharmacopoeia standards of various countries, the detection wavelength of related substances in this product is proposed to be 230nm.

[0092] (2) According to the localization spectrum of each impurity, the peak shape of the main peak and each impurity peak is good, and the separation between each impurity peak and the main peak and the blank excipient peak is good. However, the separation between impurity A, impurity B and impurity H is poor, especially impurity B and impurity H. The two failed to achieve baseline separation, and the analysis method of related substances of this product needs to be further optimized.

[0093] Example 2 Optimization of chromatographic conditions ① (0.1% perchloric acid solution-acetonitrile system)

[0094] This method is an improvement upon the chromatographic conditions (ion-pairing reagent) for related substances in the imported drug registration standard (JX20240025). It uses perchloric acid aqueous solution instead of ion-pairing reagent. This system eliminates the need for long-chain alkyl ion-pairing reagents, simplifies mobile phase preparation, enables rapid system equilibration, provides a stable baseline, minimizes column damage, and enhances method robustness, making it more suitable for routine detection of related substances in this product. The optimized chromatographic conditions and results are as follows:

[0095] Table 8 Optimization of Chromatographic Conditions ① Chromatographic Conditions

[0096] Mobile phase A 0.1% perchloric acid aqueous solution Mobile phase B Acetonitrile Detection wavelength 230nm Flow rate 1ml / min Column temperature 30℃ Injection volume 10μl runtime 30min Washing process Mobile phase A:Mobile phase B = 70:30

[0097] Experimental results:

[0098] The UV full-wavelength scan of impurity A (0.1% perchloric acid solution-acetonitrile system) is shown below. Figure 6 ; Optimization of chromatographic conditions ① Impurity localization chromatograms are shown in Figure 7 .

[0099] in conclusion:

[0100] (1) The experimental results show that the peaks of impurity A and impurity B in the 0.1% perchloric acid solution-acetonitrile system have good peak shapes with the main peak of lidocaine, and the separation between lidocaine and each impurity is good. However, the chromatographic response of impurity A is significantly low, and the detection sensitivity cannot meet the requirements.

[0101] (2) Compared with the related substances method of EP-12.3 / USP-2026, the 0.1% perchloric acid solution-acetonitrile system significantly reduced the pH value of the mobile phase. Therefore, in this mobile phase system, a diode array detector was used to perform a full wavelength scan of impurity A in the wavelength range of 190nm to 400nm. The results showed that in the 0.1% perchloric acid solution system, the maximum absorption wavelength of impurity A was significantly shifted, and it had almost no ultraviolet absorption characteristics at a wavelength of 230nm.

[0102] (3) Further analysis shows that impurity A (2,6-dimethylaniline) is an aromatic amine compound. In the strongly acidic perchloric acid system, it is in a fully protonated state. After the nitrogen atom of the aromatic amine is protonated, the molecular conjugated system is destroyed, resulting in a significant decrease in its ultraviolet absorption intensity and a blue shift in the maximum absorption wavelength. However, in the near-neutral pH 8.0 system, the compound mainly exists in molecular form with a complete conjugated structure and a significantly enhanced ultraviolet absorption response, which is more conducive to the sensitive detection of low-concentration impurities.

[0103] (4) In summary, the 0.1% perchloric acid solution-acetonitrile system cannot meet the detection sensitivity requirements of impurity A and is not suitable for the detection of related substances in this product. The next step will be to continue to optimize the analytical method for related substances in this product based on the pH 8.0 phosphate buffer system.

[0104] Example 3 Optimization of Chromatographic Conditions ② (pH 8.0 phosphate buffer system - gradient elution)

[0105] Since the results of Example 2 were unsatisfactory, a review of the experimental results of reproducing the analytical methods for related substances in the EP-12.3 / USP-2026 standard revealed that the detection sensitivity of lidocaine and its various impurities was not a problem. Only the separation between impurity peaks A, B, and H was poor. Therefore, the mobile phase elution procedure in the EP-12.3 / USP-2026 standard can be appropriately optimized to improve the separation between the impurities.

[0106] Table 9 Optimization of Chromatographic Conditions ② Chromatographic Conditions

[0107] Mobile phase A Potassium dihydrogen phosphate solution (pH 8.0) Mobile phase B Acetonitrile Detection wavelength 230nm Flow rate 1ml / min Column temperature 30℃ Injection volume 10μl Washing process See Tables 10 and 11 below.

[0108] Table 10 Optimization of Chromatographic Conditions ② Elution Program 1

[0109] 0 90 10 3 90 10 15 50 50 20 50 50 21 30 70 30 30 70 31 90 10 40 90 10

[0110] Table 11 Optimization of Chromatographic Conditions ② Elution Program 2

[0111] 0 95 5 20 50 50 21 95 5 30 95 5

[0112] Experimental results:

[0113] Optimization of chromatographic conditions ② Impurity localization map (elution program 1) See Figure 8 ; Optimization of chromatographic conditions ② Impurity localization map (elution program 2) see Figure 9 .

[0114] in conclusion:

[0115] Based on the analytical methods for related substances in the EP-12.3 / USP-2026 standard, the elution program of the mobile phase was optimized. The results showed that the retention times of impurities A, B, and H were all prolonged, but effective separation between the peaks was not achieved; in fact, the separation degree was worse. In conclusion, simply adjusting the mobile phase elution program is insufficient to achieve effective separation of these three impurities.

[0116] Example 4 Optimization of Chromatographic Conditions ③ (pH 8.0 Phosphate Buffer System - Gradient Elution)

[0117] Adjusting the mobile phase elution program in Example 3 failed to achieve effective separation of impurities A, B, and H, thus failing to meet quality control requirements. Therefore, this experiment, based on the analytical methods for related substances in EP-12.3 / USP-2026, further explored optimization directions: replacing the column with a different model, using a YMC-Triart C18ExRS column (4.6mm × 250mm, 5μm); and increasing the proportion of organic phase in the mobile phase. The resolution between impurities A, B, and H and the main peak was the primary focus of the study. Specific chromatographic conditions are detailed in Table 12, and the experimental results are detailed in [Table 12]. Figure 10 (Chromatographic condition optimization ③ Impurity localization map).

[0118] Table 12 Optimization of Chromatographic Conditions ③ Chromatographic Conditions

[0119] Mobile phase A Potassium dihydrogen phosphate solution (pH 8.0) Mobile phase B Acetonitrile Washing process Mobile phase A:Mobile phase B = 55:45 Detection wavelength 230nm Flow rate 1ml / min Column temperature 30℃ Injection volume 10μl

[0120] Conclusion: Under the conditions of a YMC-Triart C18 ExRS (4.6 mm × 250 mm, 5 μm) column, isocratic elution with pH 8.0 phosphate solution-acetonitrile (55:45) resulted in good separation between the impurity peaks, the main peak, and the blank excipient peak; however, the peak shape of impurity B was poor. This somewhat affected the accurate quantification of impurities, and further optimization of the analytical method is still needed.

[0121] In response to the problem of severe tailing of impurity B in Example 4, solutions were explored and optimization measures were further developed: Examples 5-7.

[0122] Example 5: Optimization of Chromatographic Conditions ④-1

[0123] An experiment was conducted to add a certain proportion of the tailing agent triethylamine to mobile phase A. The improvement of impurity B peak shape by different concentrations of triethylamine was investigated. Specific chromatographic conditions are detailed in Table 13, and experimental results are detailed in [Table 13]. Figure 11 Optimization of chromatographic conditions ④ Localization chromatogram of impurity B (triethylamine at different concentrations).

[0124] Table 13 Optimization of Chromatographic Conditions ④-1 Triethylamine at Different Concentrations

[0125] Mobile phase A Potassium dihydrogen phosphate solution (4.85g potassium dihydrogen phosphate dissolved in 1000ml water, with 0.05%, 0.1%, and 0.2% triethylamine added respectively, and pH adjusted to 8.0 with saturated sodium hydroxide). Mobile phase B Acetonitrile Washing process Mobile phase A:Mobile phase B = 55:45 Detection wavelength 230nm Flow rate 1ml / min Column temperature 30℃ Injection volume 10μl

[0126] Experimental results: Due to the structural characteristics of impurity B (containing multiple base active sites), adding different concentrations of triethylamine as a tailing agent to the mobile phase could not significantly improve the tailing problem of impurity B.

[0127] Example 6 Optimization of Chromatographic Conditions ④-2

[0128] Within the column's tolerance range, the mobile phase pH was gradually increased to 11.0 to fully deprotonate the basic compounds, allowing them to exist in a neutral molecular form, no longer carrying a positive charge. This eliminated electrostatic ion interactions with silanol groups, causing secondary retention to disappear and peak shapes to become symmetrical. Specific chromatographic conditions are detailed in Table 14, and experimental results are detailed in […]. Figure 12 Chromatographic condition optimization ④-2 Impurity B localization map (different mobile phase pH values).

[0129] Table 14 Optimization of Chromatographic Conditions ④ -2 Different pH Values

[0130] Mobile phase A Potassium dihydrogen phosphate solution (4.85g potassium dihydrogen phosphate dissolved in 1000ml water, and the pH adjusted to 8.0, 10.0 and 11.0 respectively with saturated sodium hydroxide) Mobile phase B Acetonitrile Washing process Mobile phase A:Mobile phase B = 55:45 Detection wavelength 230nm Flow rate 1ml / min Column temperature 30℃ Injection volume 10μl

[0131] Experimental results: Due to the structural characteristics of impurity B (containing multiple base active sites), the tailing problem of impurity B could not be significantly improved by reasonably adjusting the pH value of the mobile phase (>pKa+2).

[0132] Example 7 Optimization of Chromatographic Conditions ④-3

[0133] Before impurity B elutes from the column, a gradient elution program is set up. As the gradient proceeds, the proportion of the organic phase gradually increases, and the elution intensity strengthens. Specific chromatographic conditions are detailed in Table 15, and experimental results are detailed in […]. Figure 13 Chromatographic condition optimization ④-3 Localization map of impurity B (different elution programs).

[0134] Table 15 Optimization of Chromatographic Conditions ④ - Gradient Elution

[0135] Mobile phase A Potassium dihydrogen phosphate solution (4.85g potassium dihydrogen phosphate dissolved in 1000ml water, pH adjusted to 8.0 with saturated sodium hydroxide) Mobile phase B Acetonitrile Detection wavelength 230nm Flow rate 1ml / min Column temperature 30℃ Injection volume 10μl Washing procedure 1 Mobile phase A:Mobile phase B = 55:45 Washing procedure 2 See Table 16 Washing procedure 3 See Table 17

[0136] Table 16 Optimization of Chromatographic Conditions ④ - Gradient Elution Elution Program 2

[0137] 0 70 30 20 30 70 25 30 70 26 70 30

[0138] Table 17 Optimization of Chromatographic Conditions ④ - Gradient Elution Elution Program 3

[0139] 0 55 45 10 55 45 20 30 70 30 30 70 31 55 45 40 55 45

[0140] Experimental results: Due to the structural characteristics of impurity B (containing multiple base active sites), the tailing problem of impurity B could not be significantly improved by setting a gradient elution program.

[0141] As can be seen from Examples 5-7, due to the structural characteristics of impurity B (containing multiple base active sites), the tailing problem of impurity B cannot be significantly improved by adding different concentrations of triethylamine as a tailing agent to the mobile phase, reasonably adjusting the pH value of the mobile phase (>pKa+2), and setting a gradient elution program. That is, conventional and common technical means cannot improve the tailing problem of impurity B.

[0142] Example 8 Column Optimization ⑤

[0143] Based on the related substances analysis method in EP-12.3 / USP-2026 standard, the chromatographic column was changed to a WatersXterra RP18 column (4.6 mm × 250 mm, 5 μm), and the effect of different column temperatures on the resolution of various impurities was investigated. Specific chromatographic conditions are detailed in Table 18, and experimental results are detailed in [Table 18]. Figure 14 , 15 16.

[0144] Table 18 Optimization of Chromatographic Conditions ⑤ Method Parameters

[0145] Mobile phase A Potassium dihydrogen phosphate solution (pH 8.0) Mobile phase B Acetonitrile Washing process Mobile phase A:Mobile phase B = 65:35 Detection wavelength 230nm Flow rate 1ml / min Column temperature 30℃ or 40℃ or 45℃ Injection volume 10μl

[0146] As can be seen, replacing the column with a Waters Xterra RP18 (4.6mm × 250mm, 5μm) significantly improved the peak shape of impurity B. It was also found that the retention of impurity B was relatively sensitive to column temperature; at a column temperature of 40℃, impurities A, B, and H were well separated.

[0147] Example 9 Column Optimization ⑥

[0148] Based on the chromatographic conditions of Example 8 (column temperature 40℃), the effect of the pH value of mobile phase A (pH 7.8, pH 8.0, pH 8.2) on the resolution of each impurity was further investigated, i.e., the robustness of the mobile phase pH was examined. Specific chromatographic conditions are detailed in Table 19, and experimental results are detailed in […]. Figure 17 , 18 19.

[0149] Table 19 Optimization of Chromatographic Conditions ⑥ Method Parameters

[0150] Mobile phase A Potassium dihydrogen phosphate solution (pH 7.8, pH 8.0, or pH 8.2) Mobile phase B Acetonitrile Washing process Mobile phase A:Mobile phase B = 65:35 Detection wavelength 230nm Flow rate 1ml / min Column temperature 40℃ Injection volume 10μl

[0151] It is evident that when the pH of mobile phase A is 8.0, the impurities are well separated from each other and from the excipient peak; when the pH of mobile phase A is 7.8, impurity B and impurity H cannot be effectively separated; and when the pH of mobile phase A is 8.2, impurity B and the excipient peak (propylparaben) cannot be effectively separated. Therefore, the pH robustness of mobile phase A in this analytical method is poor, and the analytical method carries inherent risks.

[0152] However, the experimental results further revealed that the separation between impurities and between impurity peaks and those of excipients is highly sensitive to pH changes, indicating a potential risk of poor impurity separation in the analytical method. Therefore, setting the pH of mobile phase A to 8.0 is not the optimal choice.

[0153] Example 10 Column Optimization ⑦

[0154] Based on the above experimental results, the inventors, considering the physicochemical properties of lidocaine and its impurities (all basic compounds), continued to explore the effect of increasing the pH value of mobile phase A on the experiment, within the tolerance range of the chromatographic column. Specific chromatographic conditions are detailed in Table 20, and experimental results are detailed in […]. Figure 20 , 21 ,twenty two.

[0155] Table 20 Optimization of Chromatographic Conditions ⑦ Method Parameters

[0156] Mobile phase A Potassium dihydrogen phosphate solutions (pH 9.0, pH 9.5, pH 10.0) Mobile phase B Acetonitrile Washing process Mobile phase A:Mobile phase B = 65:35 Detection wavelength 230nm Flow rate 1ml / min Column temperature 40℃ Injection volume 10μl runtime 40min

[0157] The experimental results show that when the pH of mobile phase A is increased to 9.0, the separation between the impurities and between the impurities and the excipient peaks is good, but the elution order changes. Under this chromatographic condition, the elution order of each component peak is as follows: methylparaben, propylparaben, impurity H, impurity A, impurity B, and lidocaine.

[0158] Further increasing the pH of mobile phase A to 9.5 and 10.0 resulted in better separation between impurities and between impurity peaks and excipient peaks. Considering all factors, a mobile phase pH of 9.5 was selected as the method for detecting related substances in lidocaine gel patches.

[0159] Example 11 Column Optimization⑧

[0160] Based on Example 10, further exploration was conducted: In the experimental results of Example 10, impurity B and lidocaine showed late elution times and insufficiently sharp peak shapes. A gradient elution program was attempted to improve this; simultaneously, the elution intensity of the mobile phase was increased to ensure the effective elution of other strongly retained components in the test solution, thereby improving the specificity and accuracy of the analytical method. Specific chromatographic conditions are detailed in Table 21, and experimental results are detailed in […]. Figure 23 .

[0161] Table 21 Parameters for Optimization of Chromatographic Conditions (⑧)

[0162] Mobile phase A Potassium dihydrogen phosphate solution (pH 9.5) Mobile phase B Acetonitrile Detection wavelength 230nm Flow rate 1ml / min Column temperature 40℃ Injection volume 10μl Washing process See Table 22 below

[0163] Table 22 Optimization of Chromatographic Conditions ⑧ Elution Procedure

[0164] 0 65 35 10 65 35 20 40 60 30 40 60 31 65 35 40 65 35

[0165] It can be seen that after setting gradient elution, the peaks of impurity B and lidocaine were further improved, and the unknown strongly retained excipient components in the blank excipient solution were also effectively eluted.

[0166] Example 12 Analytical Method Validation

[0167] 1. Exclusivity

[0168] 1.1 Solution preparation:

[0169] (1) Blank solvent: methanol

[0170] (2) Blank excipient solution:

[0171] Take one lidocaine blank patch, cut it into small pieces, remove the release film, and place it in an Erlenmeyer flask containing 80 ml of solvent, ensuring the solvent completely submerges the sample. Sonicate for 60 min, then transfer it to a 250 ml volumetric flask. Add another 80 ml of solvent to the Erlenmeyer flask, sonicate for another 60 min, and then transfer it to the same 250 ml volumetric flask. Repeat this process once, starting from the step of "adding another 80 ml of solvent to the Erlenmeyer flask." After cooling, dilute to the mark with solvent, shake well, and collect the filtrate.

[0172] (3) Impurity stock solution:

[0173] Impurity A stock solution: Accurately weigh 11.2 mg of lidocaine impurity A, place it in a 100 ml volumetric flask, dissolve and dilute to the mark with solvent, and shake well. (112 μg / ml)

[0174] Impurity B stock solution: Accurately weigh 11.2 mg of lidocaine impurity B, place it in a 20 ml volumetric flask, dissolve and dilute to the mark with solvent, and shake well. (560 μg / ml)

[0175] Impurity H stock solution: Accurately weigh 11.2 mg of lidocaine impurity H, place it in a 20 ml volumetric flask, dissolve and dilute to the mark with solvent, and shake well. (560 μg / ml)

[0176] (4) Mixed solution of impurities

[0177] Accurately measure 5 ml of impurity A stock solution, 2.5 ml each of impurity B stock solution and impurity H stock solution, place them in the same 50 ml volumetric flask, dilute to the mark with solvent, and shake well to obtain the impurity mixed solution.

[0178] (5) Spiked test solution: Take one patch of this product, cut a 6cm diameter circular slice from the middle part, cut it into small pieces, remove the release film and place it in an Erlenmeyer flask containing 15ml of solvent, accurately add 5ml of impurity mixture solution, sonicate for 60min, transfer to a 50ml volumetric flask, add 15ml of solvent to the Erlenmeyer flask again, sonicate for 60min and transfer to the same 50ml volumetric flask. Repeat the operation once from "add 15ml of solvent to the Erlenmeyer flask again", cool and dilute to the mark with solvent, shake well, filter, and take the filtrate.

[0179] 1.2 Test Results:

[0180]

[0181] 2. System Applicability

[0182] 2.1 Solution Preparation

[0183] (1) Impurity mixture solution: Impurity mixture solution under the same specificity item

[0184] (2) System suitability solution: Weigh 56 mg of lidocaine raw material accurately, place it in a 20 ml volumetric flask, add 2 ml of impurity mixture solution accurately, dissolve and dilute to the mark with solvent, shake well, and the solution is ready.

[0185] 2.2 Test Results

[0186]

[0187] 3. Linear

[0188] 3.1 Solution preparation:

[0189] (1) Reference stock solution: Accurately weigh 11.2 mg of lidocaine reference standard, place it in a 20 ml volumetric flask, dissolve and dilute to the mark with solvent, and shake well. (560 μg / ml)

[0190] (2) Impurity stock solution: Impurity stock solution under the same specific item.

[0191] (3) Linear stock solution: Accurately measure 5 ml of impurity A stock solution, 2.5 ml each of impurity B stock solution, impurity H stock solution and reference stock solution, place them in the same 50 ml volumetric flask, dilute to the mark with solvent, shake well, and the solution is ready.

[0192] (4) Linear solutions: Prepare linear solutions according to the table below.

[0193] Linear-1 (LOQ) 2 100 Main component: 0.56 μg / ml; Impurity A: 0.224 μg / ml; Impurity B: 0.56 μg / ml; Impurity H: 0.56 μg / ml Linear -2 (50%) 5 100 Main component: 1.40 μg / ml; Impurity A: 0.56 μg / ml; Impurity B: 1.40 μg / ml; Impurity H: 1.40 μg / ml Linear -3 (80%) 4 50 Main component: 2.24 μg / ml; Impurity A: 0.896 μg / ml; Impurity B: 2.24 μg / ml; Impurity H: 2.24 μg / ml Linear -4 (100%) 2 20 Main component: 2.80 μg / ml; Impurity A: 1.12 μg / ml; Impurity B: 2.80 μg / ml; Impurity H: 2.80 μg / ml Linear -5 (150%) 3 20 Main component: 4.20 μg / ml; Impurity A: 1.68 μg / ml; Impurity B: 4.20 μg / ml; Impurity H: 4.20 μg / ml Linear -6 (200%) 4 20 Main component: 5.60 μg / ml; Impurity A: 2.24 μg / ml; Impurity B: 5.60 μg / ml; Impurity H: 5.60 μg / ml

[0194] 3.2 Test Results:

[0195]

[0196]

[0197]

[0198]

[0199] Verification conclusions 1. Lidocaine showed linearity in the concentration range of 0.5608 μg / ml to 5.6081 μg / ml, with a linear regression equation of y = 0.1278x + 0.0083; the correlation coefficient R was 1.0000, not less than 0.990; the absolute value of the Y-intercept was 2.25%, not greater than 25%; the sum of squared residuals was 0.0000, indicating a good linear relationship. 2. Impurity A showed linearity in the concentration range of 0.2227 μg / ml to 2.2271 μg / ml, with a linear regression equation of y = 0.5617x + 0.0022; the correlation coefficient R is 1.0000, not less than 0.990; the absolute value of the Y-intercept is 0.35%, not greater than 25%; the sum of squared residuals is 0.0000, indicating a good linear relationship; 3. Impurity B shows linearity in the concentration range of 0.5608 μg / ml to 5.6079 μg / ml, with a linear regression equation of y = 1.7587x + 0.0187; the correlation coefficient R is 0.9999, not less than 0.990; the absolute value of the Y-intercept is 0.37%, not greater than 25%; the sum of squared residuals is 0.0121, indicating a good linear relationship; 4. Impurity H shows linearity in the concentration range of 0.5536 μg / ml to 5.5358 μg / ml, with a linear regression equation of y = 0.1653x + 0.0049; the correlation coefficient R is 0.9998, not less than 0.990; the absolute value of the Y-axis intercept is 1.04%, not greater than 25%; the sum of squared residuals is 0.0002, indicating a good linear relationship.

[0200] 4. Limit of Quantification and Limit of Detection

[0201] 4.1 Solution preparation:

[0202] (1) Limit of Quantitation Solution: Same as linear solution 1 (LOQ)

[0203] (2) Limit of Detection Solution: Accurately measure 5 ml of the limit of quantitation solution, place it in a 10 ml volumetric flask, dilute to the mark with solvent, and shake well to obtain the solution.

[0204] 4.2 Test Results:

[0205]

[0206]

[0207] Acceptable standards:

[0208] 1. The signal-to-noise ratio of the main peak and the peak height of each known impurity in the limit of quantitation solution should not be less than 10; 2. For six consecutive injections of the limit of quantitation solution, the RSD of the area of ​​the main peak and the peak area of ​​each known impurity should not be greater than 10%.

[0209] Verification conclusion:

[0210] 1. The limit of quantitation concentration of lidocaine is 0.56 μg / ml, which is approximately equivalent to 0.020% of the concentration of the test sample solution. After six consecutive injections, the minimum signal-to-noise ratio (S / N) is 25.2, which is greater than 10, and the RSD of the peak area is 2.0%, which is less than 10%, which meets the requirements.

[0211] 2. The limit of quantitation (LOQ) for impurity A is 0.224 μg / ml, approximately equivalent to 0.008% of the concentration of the test sample solution. Six consecutive injections were performed. The signal-to-noise ratio was [not specified].

[0212] The minimum signal-to-noise ratio (S / N) is 34.8, which is greater than 10, and the RSD of the peak area is 1.9%, which is less than 10%, meeting the requirements. 3. The limit of quantitation (LOQ) concentration for impurity B is 0.56 μg / ml, approximately equivalent to 0.020% of the concentration of the test sample solution. With 6 consecutive injections, the minimum S / N is 229.0, which is greater than 10, and the RSD of the peak area is 1.1%, which is less than 10%, meeting the requirements. 4. The limit of quantitation (LOQ) concentration for impurity H is 0.56 μg / ml, approximately equivalent to 0.020% of the concentration of the test sample solution. With 6 consecutive injections, the minimum S / N is 25.8, which is greater than 10, and the RSD of the peak area is 4.2%, which is less than 10%, meeting the requirements.

[0213] 5. Accuracy

[0214] 5.1 Solution preparation:

[0215] (1) Impurity mixture solution: Impurity mixture solution under the same specificity item

[0216] (2) Background test solution:

[0217] Take one patch of this product, cut a 6cm diameter circular slice from the middle part, mince it, remove the release film, and place it in an Erlenmeyer flask containing 15ml of solvent, ensuring the solvent completely submerges the sample. Sonicate for 60 minutes, then transfer to a 50ml volumetric flask. Add another 15ml of solvent to the Erlenmeyer flask, sonicate for another 60 minutes, and then transfer to the same 50ml volumetric flask. Repeat the operation once, starting from "add another 15ml of solvent to the Erlenmeyer flask". After cooling, dilute to the mark with solvent, shake well, filter, and collect the filtrate.

[0218] (3) Accuracy solution:

[0219] Take one patch of this product, cut a 6cm diameter circular slice from the center, mince it, remove the release membrane, and place it in an Erlenmeyer flask containing 15ml of solvent. Add an appropriate amount of accuracy stock solution according to the table below (the volume of solvent added for the first time can be reduced accordingly based on the volume of accuracy stock solution added). Sonicate for 60 minutes, transfer to a 50ml volumetric flask, add another 15ml of solvent to the Erlenmeyer flask, sonicate for another 60 minutes, and then transfer to the same 50ml volumetric flask. Repeat the operation once, starting from "add another 15ml of solvent to the Erlenmeyer flask". After cooling, dilute to the mark with solvent, shake well, filter, and collect the filtrate. (Prepare 3 replicates for each concentration.)

[0220] Accuracy level 1 (LOQ, 20%) 1 50 Impurity A: 0.224 μg / ml; Impurity B: 0.56 μg / ml; Impurity H: 0.56 μg / ml Accuracy level 2 (50%) 2.5 50 Impurity A: 0.56 μg / ml; Impurity B: 1.4 μg / ml; Impurity H: 1.4 μg / ml Accuracy level 3 (100%) 5 50 Impurity A: 1.12 μg / ml; Impurity B: 2.8 μg / ml; Impurity H: 2.8 μg / ml Accuracy level 4 (150%) 7.5 50 Impurity A: 1.68 μg / ml; Impurity B: 4.2 μg / ml; Impurity H: 4.2 μg / ml

[0221] 5.2 Test Results:

[0222]

[0223]

[0224] Example 13 Related Matter Calculation Method

[0225] Referring to EP-12.3 / USP-2026 standards and Lidoderm's imported drug registration standard (JX20240025), the limits for impurity A are set at 0.04%, impurity B at 0.1%, and other single unknown impurities at 0.1%. Using the above limit concentrations as the 100% linear concentration, a series of linear solutions of impurity A, impurity B, and lidocaine within the limit concentration range of 20% to 200% are prepared respectively. The linear relationship of the three within this concentration range is examined, and the correction factor for the impurities is calculated.

[0226] Table 23 Correction factors for each impurity

[0227] Lidocaine 0.1278 / Impurity A 0.5617 0.23 Impurity B 1.7587 0.07

[0228] in conclusion:

[0229] (1) The correction factor for impurity A is 0.23 and the correction factor for impurity B is 0.07.

[0230] (2) Based on the correction factor results of impurity A and impurity B, and with reference to the Lidoderm Imported Drug Registration Standard (JX20240025), it was finally determined that impurity A and impurity B were quantitatively calculated using the external standard method; unknown impurities were quantitatively calculated using the principal component external standard method, and unknown impurities less than 0.02% were ignored.

Claims

1. A method for detecting related substances in lidocaine gel patches and its application, characterized in that, A high-performance liquid chromatography (HPLC) method was used to detect related substances in lidocaine gel patches containing lidocaine, urea, and methylparaben and / or propylparaben. The method includes the following steps: (1) Preparation of the test solution; (2) Preparation of reference solution; (3) Chromatographic detection conditions include: Column: Waters Xterra RP18, 4.6 mm × 250 mm, with a particle size of 5 μm; Column temperature: 30-40℃; Mobile phase: Potassium dihydrogen phosphate solution is used as mobile phase A, and acetonitrile is used as mobile phase B. The mobile phase A is made by dissolving and diluting potassium dihydrogen phosphate with water and adjusting the pH to 9-10. The detection wavelength is 230 nm; The gradient elution program is as follows: 0-10 min, mobile phase A 60-70%, mobile phase B 30-40%; 10-20 min, mobile phase A 35-45%, mobile phase B 55-65%; 20-30 min, maintain mobile phase A at 35-45%, mobile phase B at 55-65%; 30-40 min, mobile phase A at 60-70%, mobile phase B at 30-40%. (4) Using the reference solutions prepared with impurity A reference standard, impurity B reference standard and lidocaine reference standard as references, the impurities A, B and other related substances in the test solution are quantified; among them, impurities A and B are quantified by the external standard method of the corresponding reference standards, and other related substances are quantified by the external standard method of lidocaine reference standard.

2. The detection method according to claim 1, characterized in that, Potassium dihydrogen phosphate solution was used as mobile phase A, and acetonitrile was used as mobile phase B. The mobile phase A was made by dissolving and diluting potassium dihydrogen phosphate in water and adjusting the pH to 9.

5.

3. The detection method according to claim 2, characterized in that, The column temperature is 40℃.

4. The detection method according to claim 3, characterized in that, Flow rate: 1.0 ml / min; Detection wavelength: 230 nm.

5. A method for detecting related substances in lidocaine gel patches, characterized in that, High-performance liquid chromatography (HPLC) was used to detect related substances in lidocaine gel patches containing lidocaine, urea, and methylparaben and / or propylparaben. The detection conditions are shown in the table below:

6. The detection method according to claim 5, characterized in that, Its gradient elution procedure is as follows:

7. The detection method according to claim 6, wherein the detection object is a gel patch substrate containing lidocaine, urea, methylparaben and / or propylparaben.

8. The detection method according to claim 7, wherein the detection object is lidocaine gel patch and its generic drug.

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