Bioequivalence (BE) research plays an important role in the research and development of innovative drugs, post-market evaluation of drugs, and consistency evaluation of generic drugs.

Inhalation administration is the preferred method of administration for the prevention and treatment of respiratory diseases such as asthma and chronic obstructive pulmonary disease. However, since the dosage form, device and mode of action of inhalants are special compared with ordinary preparations, the bioequivalence study of inhalant imitation products Generally more difficult.

This article mainly compares and introduces the evaluation methods of the bioequivalence study of inhalation preparations (including oral inhalation preparations and nasal sprays) issued by the US FDA, Europe EMA and Health Canada (HC) and the "Oral Inhalation Preparations" issued by CDE The "Guiding Principles for the Study of Generic Pharmacy and Human Bioequivalence" for comments, combined with specific examples to analyze the main points and difficulties, and briefly introduce the Australian Medical Goods Administration (Therapeutic Goods Administration, TGA) bioequivalence evaluation method, It hopes to provide a scientific reference for the research on the bioequivalence of relevant inhalation preparations and the development of policies and regulations in China.

Evaluation method of inhalation bioequivalence study

U.S. FDA evaluation method

The FDA recommends using the weight of evidence method for BE studies of inhaled drug products (IDP).

This method judges the equivalence of dosing on the basis of all data obtained from appropriate in vitro studies, pharmacokinetics (PK) studies, and pharmacodynamics (PD, or clinical efficacy) studies. While ensuring equivalence and patient compliance with alternative medicines, the similarity between prescriptions and drug delivery devices is also considered, as shown in Figure 1.

To draw the conclusion that the two preparations are bioequivalent, it is necessary to meet the four key points of prescription and drug delivery device similarity, in vitro test equivalence, system exposure PK study equivalence, and PD and clinical study equivalence, otherwise the bioequivalence will not be established.

European EMA Evaluation Method

The EMA guidelines use a step-by-step evaluation method to evaluate the bioequivalence of inhalants. This method takes in vitro research as the first step. If the in vitro research results meet specific equivalence standards, the two preparations can be directly determined to be bioequivalent; if the in vitro research results do not meet the bioequivalence standards, pharmacokinetic studies are required, including Assessment of lung and systemic bioavailability.

If the results of the pharmacokinetic study still do not meet the equivalence standard, the third step is to use pharmacodynamic and clinical endpoint studies to prove local bioequivalence (see Figure 2); if the bioequivalence can be proved through pharmacokinetic studies, There is no need for further large-scale pharmacodynamics and clinical efficacy studies.

Canadian HC and Australian TGA evaluation methods

Although HC does not clearly indicate the type of evaluation method used in the guidelines, the method it adopts is similar to the weight of evidence method used by the FDA: it requires the use of in vitro analysis and all data from PK and PD studies for bioequivalence judgment.

In some studies of bioequivalence evaluation of TGA, the guidelines issued by EMA and FDA (mainly refer to EMA) are referenced. The evaluation methods are different for different types of inhaled drugs, but the method of stepwise evaluation is mainly adopted, such as metered inhalation. For the evaluation of drug bioequivalence, since most of the guidelines of TGA directly refer to the requirements of the guidelines issued by EMA, it will not be described in detail below.

China CDE Evaluation Method

The comment draft issued by CDE also does not indicate the type of evaluation method used. The method refers to the relevant research technology and statistical guidelines issued by the National Medical Products Administration (NMPA) and the related issues issued by the FDA and EMA. The guideline determines the bioequivalence of the two preparations by judging whether they meet both pharmaceutical research equivalence and human bioequivalence (PK, PD and clinical research equivalence), similar to the FDA's weight of evidence method.

Study on the bioequivalence of inhalants

Pharmaceutical Research Evaluation

1. Selection of reference preparations

FDA and HC recommend to choose from the reference listed drug (RLD) in their country, such as the "Drugs Approved for Evaluation of Bioequivalence" (Orange Book) published by the FDA. If a foreign reference drug is used, a certification is required. This reference preparation is exactly the same as the domestic reference preparation, and similar reference preparations are not accepted.

EMA proposes that as long as it is an original drug approved by a designated agency, it can be used as a reference drug. NMPA pointed out in the guidelines that in order to ensure the quality of generic drugs, the original product should be selected as the reference preparation as far as possible in the bioequivalence test of generic drugs.

2. In vitro bioequivalence study

Due to the characteristics of inhaled preparations, the bioequivalence evidence obtained from in vitro studies is relatively stable and sensitive to differences between preparations. Therefore, in vitro studies play a vital role in judging the bioequivalence of inhaled preparations.

In the EMA guidelines, in vitro test results can be used alone as the basis for bioequivalence judgment. In other countries, when in vivo pharmacokinetic or pharmacodynamic studies cannot be conducted, in vitro test results can also be used as an important additional evidence of bioequivalence.

In vitro studies not only need to assess the similarity of test and reference formulations and devices, but also need to conduct comparative studies on drug delivery dose and aerodynamic particle size distribution. Because these factors will affect the aerodynamic performance of the drug, thereby affecting the amount of drug deposited in the lungs, and then affecting the clinical efficacy of the drug.

For example, when Singh et al. evaluated the pharmacodynamics and safety of a new dry powder inhaler of tiotropium bromide, PUR0200, they found that when the test formulation has a larger proportion of fine particles than the reference formulation, The active ingredients in the tested preparations have a higher proportion of deposits in the lungs, their systemic exposures are lower, and their clinical efficacy and safety are better.

Perry et al. also concluded that the pharmacokinetics and efficacy equivalence of inhaled preparations can be preliminarily predicted by the particle size.

Most of the literature in the in vitro studies on the bioequivalence of the two preparations are conducted to evaluate the in vitro equivalence of the composition and device, the uniformity of the delivered dose, and the aerodynamic particle size, such as Srichana and Ammari. .

When Boehringer Ingelheim conducted an in vitro test study on a new dry powder inhaler containing tiotropium bromide and salmeterol, a comparative study conducted in accordance with the EMA guidelines found that the test and reference preparations are not only similar in pharmaceutical composition and device, but also Moreover, the difference between the mass of the cascade impactor and the mass of the fine particles in the aerodynamic study is within the acceptable range (±15%), so the two preparations are judged to be equivalent in vitro. Table 1 summarizes the international and domestic guidelines and recommendations for in vitro testing studies in bioequivalence studies.

Bioequivalence study in humans

In vivo studies of the bioequivalence of inhalants include PK, PD, and clinical endpoint studies.

FDA approved Advair Diskus's first generic formulation of fluticasone/salmeterol dry powder inhalation (Wixela Inhub) in 2019, and conducted PK and PD studies in healthy subjects and asthma patients. PK judgment criteria The area under the concentration-time curve (AUC) and the peak plasma concentration (Cmax) are the 90% confidence intervals of the geometric mean ratio of the test and reference preparations. Whether the 90% confidence interval is within the bioequivalence range specified by the FDA. The main indicator of PD is Forced expiratory volume in the first second (FEV1).

The main purpose of human PK studies is to determine the systemic exposure of active molecules of inhaled drugs to monitor the safety of the tested preparations. For example, when the aforementioned Singh et al. evaluated the safety of a new tiotropium bromide dry powder inhaler PUR0200, they found that the systemic exposure of the test formulation was lower, and the incidence of adverse reactions was also lower. Security is better.

When Algorta et al. studied the BE of a new type of tiotropium monosaccharide capsule dry powder inhalation preparation in healthy volunteers, they also analyzed the systemic exposure level by measuring the drug content in the plasma to determine whether the safety of the preparation is equivalent.

PD and clinical endpoint studies are usually used to evaluate the clinical effects of local effects, and judge whether the effects are equivalent based on the primary and secondary index data. For example, Horhota et al. used FEV1 as the main PD indicator to judge the local efficacy equivalence of the tested and reference formulations when conducting pharmacodynamic research on a new type of dry powder inhaler. The following is a brief introduction and comparison of these three research methods.

1. Human PK-BE research

Since the FDA, HC and CDE require that the final equivalence result is determined by combining the data obtained from all processes in vitro and in vivo, the purpose of PK studies on inhaled preparations is only to compare the systemic exposure and safety of the test preparation and the reference preparation.

However, EMA can draw equivalence conclusions solely through PK studies, so its PK study equivalence requires a higher standard, and the purpose of the study is not limited to systemic exposure and safety studies, but also includes the elimination of the absorption of active ingredients in the gastrointestinal tract. Under the premise of the comparison of lung deposits.

Omar et al. pointed out that PK studies are very sensitive to small differences in drug delivery between test and reference preparations, and are therefore suitable for assessing bioequivalence. The acceptable range of the 90% confidence interval of the PK bioequivalence parameter (80.00%-125.00%) reflects the appropriate conservative range to ensure that the safety and effectiveness of the test product and the reference product are the same.

Table 2 is a comparison of international and Chinese guidelines on human PK research.

Benpromethasone dipropionate/formoterol fumarate pressurized metered-dose inhalation, salmeterol/fluticasone propionate metered-dose inhalation, budesonide/formoterol dry powder inhalation, salbutamol aerosol, etc. The preparations have been subjected to in vivo PK studies. Through statistical analysis of the PK parameters AUC and Cmax, the equivalence of the test preparation and the reference preparation in terms of PK is judged to support the bioequivalence evaluation of the drug.

2. Human PD-BE and clinical endpoint study

The methods of using PD and clinical endpoint studies are mentioned in each bioequivalence study guideline. The method should include proving that the tested and reference preparations are equivalent in efficacy and system safety. For example, Kuna et al., in the PD study of p-phenylpromethasone dipropionate/formoterol fumarate pressurized metered dose inhalation in 30 adolescents with asthma, not only detected the plasma potassium and glucose between the two groups PD variables such as, pulse and pulmonary function are used to judge the efficacy equivalence, and the content of active ingredients of the drug in the subject’s plasma is also measured to calculate the PK parameter, which is used to determine the systemic exposure of the drug, that is, whether the safety is equivalent.

Singh et al. studied the bioequivalence of a new dry powder inhaler of Tiotropium Bromide PUR0200 and the reference preparation Tiotropium Bromide HH, not only studied the main PD variable: the area under the curve of FEV1 to judge the efficacy equivalence , Also studied the calculation of PK parameters to determine whether the systemic exposures of the two preparations are equivalent.

Bhattacharya et al. demonstrated that a new hydrofluoroalkane-containing pressure metered dose inhaler is clinically non-inferior for the treatment of chronic obstructive pulmonary disease compared with traditional chlorofluorocarbon pressure metered dose inhalers, and is also evaluating the main PD variables (FEV1) The systemic exposure evaluation of the drug was performed at the same time as the change. Table 3 is a comparison of international and domestic guidelines for human PD and clinical endpoint research.

At present, many inhaled preparations on the market are composed of glucocorticoid drugs. When evaluating the bioequivalence of these hormone-containing drugs, it is necessary to monitor the effect of hormones on the hypothalamus-pituitary-adrenal (hypothalamic-pituitary-adrenal, HPA). ) Axis to prove that the test formulation has no greater impact on the HPA axis than the reference formulation.

In addition to the above several PD indicators, under special circumstances, more sensitive and effective efficacy indicators can also be used. For example, studies have shown that methacholine is used for bronchial stimulation, and FEV1 as a pharmacodynamic indicator is the most sensitive method to determine the inhaled bronchodilator BE. However, many children cannot perform reproducible spirometry.

Mondal et al. aimed to study whether methacholine excitation can distinguish two salmeterol inhalants when the data obtained by pulse oscillation technology is used as a PD indicator. The test subjects were 10 patients with mild stable asthma aged 4 to 11 years old. The methacholine challenge was performed after inhaling the test preparation or the reference preparation, and the methacholine challenge concentration at which the total airway resistance increased by 40% was calculated. . The results show that using the data obtained by pulse oscillation technology as a PD indicator is also an effective method to determine the bioequivalence of inhalants for children.

Analysis of key points and difficulties in inhalation bioequivalence research

In vitro studies

In vitro research methods for inhaled preparations are generally more rigorous, with stable data, and sensitive to differences between preparations. However, the processes experienced by drugs in vitro and in vivo are not completely the same. Therefore, the results of in vitro drug research cannot fully represent the in vivo process of drugs.

Horhota et al. conducted an in vitro test study on a new type of dry powder inhaler containing tiotropium bromide and salmeterol and found that the mass of the cascade impactor and the mass of aerodynamic fine particles were similar to those of the reference formulation: the difference was <15%, In line with the conditions of in vitro bioequivalence, no significant difference was found in PD indicators in vivo. However, in the in vivo PK study, due to the high urinary excretion of the tested preparation, there are significant differences in AUC and Cmax and other indicators, and the PK study is not equivalent, indicating that the in vitro results of the inhaled preparation cannot well predict the clinical PK findings.

Therefore, the establishment of an in vitro-in vivo correlation (IVIVC) evaluation method is essential for in vitro tests to better predict in vivo results.

The EMA concept document on the revision of the clinical requirements guidelines for oral inhalation products also mentioned the importance of IVIVC study data for BE studies. Lahelma et al. was able to obtain approval in Europe for a newly developed dry powder inhaler containing budesonide and formoterol fumarate dihydrate based on the prediction results of IVIVC modeling and a number of PK studies. , Used as an alternative to Sibica Tubao to treat asthma and chronic obstructive pulmonary disease.

The development of IVIVC evaluation methods for inhaled preparations has also attracted the interest of many researchers. For example, Weers et al.'s research on establishing the relationship between aerosol performance and PK and PD of IVIVC shows that under test conditions, the real laryngeal model can be used in the lungs. Provides good IVIVC in terms of deposition and drug system exposure levels (the difference from the average in vivo measurement value is 5% to 15%).

The Office of Generic Drugs (OGD) of the FDA is also undertaking technical development that combines in vitro testing with computer technology to better predict the in vivo process of drugs: FDA in 2016 for oral inhalation and nasal drug products with local effects According to the regulatory scientific report, OGD is developing computational fluid dynamics (CFD) and physiology-based pharmacokinetic (PBPK) models to predict the process of inhaled preparations in the human body and evaluate them Applicability in generic drug development plans.

Therefore, continuing to develop a reasonable IVIVC evaluation method is of far-reaching significance for better carrying out and standardizing the BE evaluation of inhaled preparations, as well as reducing costs and improving time efficiency.

In vivo PK study

For general oral preparations that exert systemic effects, the difference between the PK parameters of the test preparation or the reference preparation is within an acceptable range, and the bioequivalence can usually be considered. However, after the inhaled preparation enters the body, it is first distributed to the site of action, then enters the systemic circulation, and also enters the systemic circulation through other parts (such as mouth, pharynx, gastrointestinal tract, etc.). The relationship between pharmacokinetics and local delivery equivalence complex.

In the EMA guidelines, there are two purposes for PK research. One is to evaluate lung deposition, and the other is to study systemic exposure to evaluate safety.

When PK studies are used to assess lung deposition, the absorption of active ingredients from the gastrointestinal tract should be excluded. In the EMA oral inhalation product guidelines, it is required to distinguish between the efficacy-related lung exposure and the total systemic exposure that occurs after oral inhalation product administration Open.

Methods of distinguishing between pulmonary contact and non-pulmonary contact include fluorescence imaging and oral charcoal block. At present, fluorescence imaging has not been accepted as a method to determine bioequivalence, mainly because the radiolabeling of the reference preparation is very complicated. The oral charcoal block method has great advantages in distinguishing pulmonary exposure from non-pulmonary exposure when evaluating oral inhalation products. It has been widely used and has been written into the EMA guidelines.

When using various methods to exclude active ingredients from being absorbed, it is necessary to ensure and prove the accuracy of the data. In addition to assessing lung deposits, international PK studies require assessment of systemic exposure to evaluate drug safety. Special attention should be paid to the research dose and the selection of subjects involved in the assessment of systemic exposure.

The FDA stipulates that the dose of the drug used in the PK study of inhalants should be able to obtain the PK study curve through sensitive analysis and detection methods. The determination of analytical testing methods and the determination of final drug doses are difficult points that need to be carefully considered in PK research. Relevant FDA studies have shown that the PK data of healthy subjects is usually more stable than the PK data of the patient, which may be related to various changes in the patient's body and disease-related. Therefore, the FDA requires healthy adult subjects for the subjects in the inhalation PK study, in order to obtain more stable data on the difference between the test preparation and the reference preparation to judge the equivalence.

In vivo PD and clinical endpoint study

The choice of PD index should be a single index or a composite index that can best show the effect of the drug. In the study of PD and clinical efficacy, the selection of drug dosage and PD index sensitive determination methods and evaluation standards all have a very significant impact on the test.

Therefore, the selection of these indicators and methods is also a major difficulty in bioequivalence research, and it is necessary to finalize effective indicators through a large amount of data and reports or research on experiments and experiments. For example, in the assessment of asthma control, the determination of asthma status and outcome indicators is very important for clinical efficacy research. Devadason and others divided into multiple research teams to finalize the composite indicators for asthma control assessment by reading and studying nearly 500 articles. .

This article reviews the similarities and differences of the guidelines for inhalation bioequivalence studies in the United States, the European Union, Canada and China.

Bioequivalence studies mainly include three phases: in vitro testing, in vivo PK studies, and PD and clinical endpoint studies. However, the priority of each phase and the design method are different in different countries.

Guidelines for the design of inhalation bioequivalence studies are very important. Zeng et al. improved the FDA’s guidelines for salbutamol bioequivalence evaluation and found that when the study dose is changed reasonably, the sample size and research cost can be effective. reduce. Therefore, we need to learn more about the relevant guidelines in more regions to enrich our understanding of the bioequivalence evaluation of inhalation preparations, in order to obtain more efficient guidelines for the development of domestic inhalation preparations.

Taking into account the characteristics of inhalants, in vitro, PK and PD studies of inhalants have their particularities, but the bioequivalence standards of most indicators are still compared with the T/R geometric mean ratio of the main PK parameters required by general drugs. The 90% confidence interval is 80.00%～125.00% are basically the same.

When conducting inhalation bioequivalence studies, it is necessary to consider its particularity to ensure the accuracy of the test data and conclusions, but also to consider its commonality with general preparations to better standardize the experimental research design.

At present, research on bioequivalence evaluation of inhaled preparations in various countries is still being improved and updated. More and more in vivo or in vitro models, IVIVC and PBPK technologies are used to improve the research, in order to achieve lower cost and higher efficiency. And accuracy to complete the bioequivalence evaluation. When improving the draft for comments issued by my country, while referring to the current guidelines issued by various countries, various new auxiliary research technologies that have been verified at this stage should also be referred to, so as to better promote and standardize the bioequivalence research of inhaled preparations in my country.