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Inspection and control methods of Pharmaceutical Impurities
2021-08-23
Limit inspection method for impurities:
Considering the influence of impurities in the drug, the smaller the content of impurities, the better, but if the impurities are completely removed, it will inevitably cause difficulties in production operations, increase production costs, reduce effectiveness, and increase the burden on patients economically. On the other hand, the impurity must be removed, which is not necessary for the effectiveness, storage, and preparation of the drug, and it cannot completely remove the impurities. The so-called pure is relative. As long as the impurity content in the drug is within a certain limit, it does not cause toxicity to the human body, and does not affect the efficacy and stability of the drug, it can be used for medical care. The impurity limit refers to the maximum allowable amount of impurities contained in the drug. The impurity inspections prescribed by the Pharmacopoeia are mainly limited inspections. During the inspection, it is generally not necessary to measure the exact content of impurities, as long as the content of impurities is controlled within the limit range, it is qualified.
There are three methods for the limit control of impurities in drugs: control method, sensitivity method and comparison method. The contrast method is widely used.
(1) The control method is to take a certain amount of the pure substance or reference substance of the tested impurity to prepare a standard solution, and after the same treatment with a certain amount of the test solution, compare the reaction results of the two to determine the test solution. Whether the impurity exceeds the limit. When using this type of method, pay attention to the principle of parallelism. The test solution and standard solution should be reacted under exactly the same conditions, such as the added reagents, reaction temperature, and storage time. Only in this way can the results of the reaction be comparable.
(2) Sensitivity method is to add reagents to the test solution, react under certain conditions, observe whether there is a positive reaction, and if there is no positive reaction, it is qualified, that is, the sensitivity of the reaction under the detection conditions is used to control the impurity limit. For example, the inspection of chloride in purified water is to add dilute nitric acid and silver nitrate test solution to 50ml sample, and no turbidity should occur. No reference substance is required for this method.
(3) The comparison method requires certain measured values (such as pH value, residue on ignition, loss on drying, absorbance, etc.) to not exceed the limit value or range. Such as penicillin sodium for injection drying at 105 ℃, the weight loss should not exceed 1.0%. No reference substance is required for this method.
Impurity control:
All impurities in the drug will affect the stability and safety of the drug to varying degrees. Therefore, it is necessary to strictly control the content of drug impurities during the production and storage of the drug. Impurity inspection is an important indicator of drug quality control. Drug impurity inspection is divided into general impurity inspection and special impurity inspection.
1. General impurity inspection
For the inspection of general impurities, the Chinese Pharmacopoeia specifies chlorides, sulfates, sulfides, selenium, fluorine, cyanides, iron salts, heavy metals, arsenic salts, ammonium salts, and pH, clarity, solution color, and loss on drying. , Inspection methods and limits for items such as moisture, residue on ignition, easy carbonization, and residual organic solvents.
2. Inspection of special impurities
Special impurities usually refer to the impurities introduced during the production and storage of the drug due to factors such as the nature of the drug, the production method, and the process conditions. Such impurities vary with different drugs. Due to the variety of special impurities, the inspection methods are not all consistent. Commonly used methods are as follows:
(1) Physical method: Use the differences in smell, taste, volatility, color, solubility and optical rotation between drugs and impurities to check whether the contained impurities meet the impurity limit regulations.
(2) Chemical reaction method: usually there are methods such as volumetric analysis, gravimetric analysis, colorimetry and turbidimetry.
(3) Chemical analysis methods: UV spectrophotometry, capillary zone electrophoresis (CZE), and high performance capillary electrophoresis (HPCE) are commonly used. For example, ultraviolet spectrophotometry is used to detect the absorbance of cytidine disodium triphosphate at the wavelengths of 280nm and 260nm, and the ratio should be 2.00-2.20; use HPCE to separate and determine the Z, E isomers and tetracycline of toremifene citrate The impurities in anhydrotetracycline, anhydrosis tetracycline and chlortetracycline, etc.
(4) Chromatography: This is the most commonly used and most effective drug impurity analysis method at present. Due to the characteristics of high sensitivity, good accuracy, simplicity, ease of use, fast and efficient, etc., it is now more and more used by the pharmacopoeias of various countries for control Impurities of drugs.
Paper chromatography (P.C)
Take a certain amount of the impurity limit control solution of the test product, spot the sample on the same chromatographic filter paper, and compare the number, color or fluorescence intensity of the impurity spots after unfolding. It is usually used for the inspection of impurities in drugs with greater polarity or radiopharmaceuticals. This method has a long time to expand, the spots are more diffuse, and corrosive coloring agents such as strong acids cannot be used, so the application range is small.
Thin layer chromatography (TLC)
Similar to the P.C method, because the method is simple and easy to implement and requires less experimental equipment, it is widely used in drug impurity inspection. There are many drugs in the pharmacopoeias of various countries that use this method to inspect the impurity of drugs. Generally, special impurities such as raw materials, intermediates, by-products or decomposition products closely related to the main drug are called related substances, and special impurities in steroid drugs are called other steroids. TLC commonly used visual comparison method to determine whether the content of impurities in the drug exceeds the limit, this is only a semi-quantitative method, and because the sensitivity is greatly affected by the operating conditions, it is sometimes difficult to meet the needs of rapid analysis.
High Performance Liquid Chromatography (HPLC)
As a relatively mature method, it has been widely used in drug impurity inspection due to its high separation efficiency, strong specificity and sensitive detection. Its impurity detection sensitivity can reach 0.1% or lower, and it can obtain very good results. The accuracy and precision, and the repeatability is good. Chromatography types with different separation mechanisms can be selected according to different analytical objects, such as normal phase, reversed phase, partitioning, etc., such as the determination of cefoperazone sodium by HPLC, and the determination of cefoperazone sodium can be used to determine impurities, and their optical isomers. Separation and quantification; cetirizine hydrochloride can be completely separated from the impurity [(4-chlorophenyl)phenylmethyl]piperazine by HPLC. However, the HPLC method also has some shortcomings. The retention time of the analysis is too long. For example, the retention time of the biserher exceeds 30min in the analysis of salbutamol and impurities. These shortcomings limit the application of HPLC in drug impurity inspection.
Gas Chromatography (GC)
It is mainly used for the inspection of volatile organic impurities and organic solvent residues, especially for the inspection of organic pesticide residues in traditional Chinese medicine. For example, the GC method is used to determine the residual amount of ethylene oxide in metronidazole; the capillary GC method is used to determine the residual amount of five organic solvents ethanol, acetone, dichloromethane, ethyl acetate, and benzene in praziquantel.
Other chromatographic methods such as Capsule Electrokinetic Chromatography (MEKC), Ion Chromatography (IC) and other methods. The IC method can be used to separate amylamine in BMS-181866-02 and tributanolamine in BMS-188494-04.
Considering the influence of impurities in the drug, the smaller the content of impurities, the better, but if the impurities are completely removed, it will inevitably cause difficulties in production operations, increase production costs, reduce effectiveness, and increase the burden on patients economically. On the other hand, the impurity must be removed, which is not necessary for the effectiveness, storage, and preparation of the drug, and it cannot completely remove the impurities. The so-called pure is relative. As long as the impurity content in the drug is within a certain limit, it does not cause toxicity to the human body, and does not affect the efficacy and stability of the drug, it can be used for medical care. The impurity limit refers to the maximum allowable amount of impurities contained in the drug. The impurity inspections prescribed by the Pharmacopoeia are mainly limited inspections. During the inspection, it is generally not necessary to measure the exact content of impurities, as long as the content of impurities is controlled within the limit range, it is qualified.
There are three methods for the limit control of impurities in drugs: control method, sensitivity method and comparison method. The contrast method is widely used.
(1) The control method is to take a certain amount of the pure substance or reference substance of the tested impurity to prepare a standard solution, and after the same treatment with a certain amount of the test solution, compare the reaction results of the two to determine the test solution. Whether the impurity exceeds the limit. When using this type of method, pay attention to the principle of parallelism. The test solution and standard solution should be reacted under exactly the same conditions, such as the added reagents, reaction temperature, and storage time. Only in this way can the results of the reaction be comparable.
(2) Sensitivity method is to add reagents to the test solution, react under certain conditions, observe whether there is a positive reaction, and if there is no positive reaction, it is qualified, that is, the sensitivity of the reaction under the detection conditions is used to control the impurity limit. For example, the inspection of chloride in purified water is to add dilute nitric acid and silver nitrate test solution to 50ml sample, and no turbidity should occur. No reference substance is required for this method.
(3) The comparison method requires certain measured values (such as pH value, residue on ignition, loss on drying, absorbance, etc.) to not exceed the limit value or range. Such as penicillin sodium for injection drying at 105 ℃, the weight loss should not exceed 1.0%. No reference substance is required for this method.
Impurity control:
All impurities in the drug will affect the stability and safety of the drug to varying degrees. Therefore, it is necessary to strictly control the content of drug impurities during the production and storage of the drug. Impurity inspection is an important indicator of drug quality control. Drug impurity inspection is divided into general impurity inspection and special impurity inspection.
1. General impurity inspection
For the inspection of general impurities, the Chinese Pharmacopoeia specifies chlorides, sulfates, sulfides, selenium, fluorine, cyanides, iron salts, heavy metals, arsenic salts, ammonium salts, and pH, clarity, solution color, and loss on drying. , Inspection methods and limits for items such as moisture, residue on ignition, easy carbonization, and residual organic solvents.
2. Inspection of special impurities
Special impurities usually refer to the impurities introduced during the production and storage of the drug due to factors such as the nature of the drug, the production method, and the process conditions. Such impurities vary with different drugs. Due to the variety of special impurities, the inspection methods are not all consistent. Commonly used methods are as follows:
(1) Physical method: Use the differences in smell, taste, volatility, color, solubility and optical rotation between drugs and impurities to check whether the contained impurities meet the impurity limit regulations.
(2) Chemical reaction method: usually there are methods such as volumetric analysis, gravimetric analysis, colorimetry and turbidimetry.
(3) Chemical analysis methods: UV spectrophotometry, capillary zone electrophoresis (CZE), and high performance capillary electrophoresis (HPCE) are commonly used. For example, ultraviolet spectrophotometry is used to detect the absorbance of cytidine disodium triphosphate at the wavelengths of 280nm and 260nm, and the ratio should be 2.00-2.20; use HPCE to separate and determine the Z, E isomers and tetracycline of toremifene citrate The impurities in anhydrotetracycline, anhydrosis tetracycline and chlortetracycline, etc.
(4) Chromatography: This is the most commonly used and most effective drug impurity analysis method at present. Due to the characteristics of high sensitivity, good accuracy, simplicity, ease of use, fast and efficient, etc., it is now more and more used by the pharmacopoeias of various countries for control Impurities of drugs.
Paper chromatography (P.C)
Take a certain amount of the impurity limit control solution of the test product, spot the sample on the same chromatographic filter paper, and compare the number, color or fluorescence intensity of the impurity spots after unfolding. It is usually used for the inspection of impurities in drugs with greater polarity or radiopharmaceuticals. This method has a long time to expand, the spots are more diffuse, and corrosive coloring agents such as strong acids cannot be used, so the application range is small.
Thin layer chromatography (TLC)
Similar to the P.C method, because the method is simple and easy to implement and requires less experimental equipment, it is widely used in drug impurity inspection. There are many drugs in the pharmacopoeias of various countries that use this method to inspect the impurity of drugs. Generally, special impurities such as raw materials, intermediates, by-products or decomposition products closely related to the main drug are called related substances, and special impurities in steroid drugs are called other steroids. TLC commonly used visual comparison method to determine whether the content of impurities in the drug exceeds the limit, this is only a semi-quantitative method, and because the sensitivity is greatly affected by the operating conditions, it is sometimes difficult to meet the needs of rapid analysis.
High Performance Liquid Chromatography (HPLC)
As a relatively mature method, it has been widely used in drug impurity inspection due to its high separation efficiency, strong specificity and sensitive detection. Its impurity detection sensitivity can reach 0.1% or lower, and it can obtain very good results. The accuracy and precision, and the repeatability is good. Chromatography types with different separation mechanisms can be selected according to different analytical objects, such as normal phase, reversed phase, partitioning, etc., such as the determination of cefoperazone sodium by HPLC, and the determination of cefoperazone sodium can be used to determine impurities, and their optical isomers. Separation and quantification; cetirizine hydrochloride can be completely separated from the impurity [(4-chlorophenyl)phenylmethyl]piperazine by HPLC. However, the HPLC method also has some shortcomings. The retention time of the analysis is too long. For example, the retention time of the biserher exceeds 30min in the analysis of salbutamol and impurities. These shortcomings limit the application of HPLC in drug impurity inspection.
Gas Chromatography (GC)
It is mainly used for the inspection of volatile organic impurities and organic solvent residues, especially for the inspection of organic pesticide residues in traditional Chinese medicine. For example, the GC method is used to determine the residual amount of ethylene oxide in metronidazole; the capillary GC method is used to determine the residual amount of five organic solvents ethanol, acetone, dichloromethane, ethyl acetate, and benzene in praziquantel.
Other chromatographic methods such as Capsule Electrokinetic Chromatography (MEKC), Ion Chromatography (IC) and other methods. The IC method can be used to separate amylamine in BMS-181866-02 and tributanolamine in BMS-188494-04.
In addition, the currently commonly used multi-method technology is gradually applied to the inspection of drug impurities. At the same time, with the continuous improvement of analytical methods, the detection methods of drug impurities have also been continuously improved, so that the separation and identification of drug impurities can be better. So as to achieve the purpose of further evaluating drug toxicity, side effects and avoiding adverse reactions. In addition to improving impurity detection methods and controlling the content of impurities, adopting appropriate methods to reduce the content of impurities and improve the efficacy of drugs is also a very important part of drug impurity control.
