Pharmacokinetic Bioequivalence between Generic and Originator Orally Inhaled Drug Products: Validity of Administration of Doses above the Approved Single Maximum Dose.

Pharmacokinetic bioequivalence of orally inhaled drug products is a critical component of the US FDA's "weight of evidence" approach, and it can serve as the sole indicator of safety and effectiveness of follow-on inhalation products approved in Europe and some other geographic areas. The approved labels of the orally inhaled drug products recommend the maximum number of actuations that can be administered in a single dose on one occasion. This single maximum dose may consist of one or more inhalations depending upon the product. Bioequivalence studies for the inhalation drug product registrations in the US and EU have employed single and multiple actuation doses, in some cases over and above the approved single maximum labeled doses, thus, inconsistent with the approved labeling of the reference products. Pharmacokinetics of inhaled drug products after single and multiple doses may be different, with implications for bioequivalence determined at single and multiple doses. Scientific literature indicates that the relative bioavailability of the Test and Reference products may differ between administrations of doses in one and multiple inhalations. Multiple doses not only alter the pharmacokinetics but also may reduce the sensitivity of the bioassay to actual differences between the Test and Reference product performances. Ability of the pharmacokinetic bioassay to accurately determine the extent of difference between two products may also be substantially reduced at high doses. Therefore, in our opinion, pharmacokinetic bioequivalence to support regulatory approvals of inhalation products at doses above the recommended single maximum dose should be avoided. Furthermore, the bioequivalence of products (if any) established at doses exceeding the approved single maximum doses should be revisited to determine if the products maintain bioequivalence when evaluated at the clinically relevant single maximum doses.

Relevance of distinctions and parallels between the US and EU guidelines for determination of comparative effectiveness and safety of the orally inhaled drug products.

Approval of drug products for market registration warrants, among other data, evidence to support their safety and effectiveness in the target populations. The extent of investigations to provide the supporting evidence varies between the new innovator products and their follow-on versions generally referred to as Generic Drugs Products in the United States and Hybrids in the Europe. The new drug applications entail large data sets encompassing both nonclinical and clinical product developments. Safety and effectiveness in man is studied in sequentially phased clinical trials, including post marketing evaluations (Where applicable). However, for the generic/hybrid products the safety and effectiveness are established through determination of bioequivalence in head-to-head comparison between the originator and the follow-ons. Methods for documentation of bioequivalence for drug products that reach target site(s) through systemic circulation are aligned worldwide. However, establishing bioequivalence of orally inhaled drug products is complex as drug delivery to the local site(s) of action is independent of the systemic circulation. Documentation of bioequivalence gets further complicated due to the Drug-Device combination nature of these products. The guidelines for establishment of BE of locally acting orally inhaled drugs products vary among certain geographies. This article examines the scientific underpinning of distinctions and similarities between the US and EU guidelines.

Conference report: Bio-International 2005.

This is a summary report of the International Pharmaceutical Federation/Board of Pharmaceutical Sciences (FIP/BPS) international conference, Bio-International 2005, which was held October 24-26, 2005 at the Royal Pharmaceutical Society, in London, UK. Bioequivalence (BE) issues related to multisource locally delivered topical dosage forms, oral inhalation drug products, highly variable drug products (HVDP), and endogenously occurring drugs were discussed. The conference also focused on alternate approaches to assess BE for some of these drug products. Pharmacokinetic (PK) approaches like, dermatopharmacokinetics (DPK) for dermatological topical dosage forms, scaled average BE (s-ABE) where within-subject variability is considered for estimation of 90% confidence intervals to document BE for highly variable drugs (HVD) were recommended. In addition, issues and difficulties related to the BE assessment of oral inhalation products, role, and appropriateness of metabolites in BE assessment, importance of base line correction in BE assessment of endogenously occurring drugs, and waiver of BE study requirements for certain drugs based on a Biopharmaceutics Classification System (BCS), were also discussed.

Product Quality Research Institute evaluation of cascade impactor profiles of pharmaceutical aerosols: part 2--evaluation of a method for determining equivalence.

The purpose of this article is to present the thought process, methods, and interim results of a PQRI Working Group, which was charged with evaluating the chi-square ratio test as a potential method for determining in vitro equivalence of aerodynamic particle size distribution (APSD) profiles obtained from cascade impactor measurements. Because this test was designed with the intention of being used as a tool in regulatory review of drug applications, the capability of the test to detect differences in APSD profiles correctly and consistently was evaluated in a systematic way across a designed space of possible profiles. To establish a "base line," properties of the test in the simplest case of pairs of identical profiles were studied. Next, the test's performance was studied with pairs of profiles, where some difference was simulated in a systematic way on a single deposition site using realistic product profiles. The results obtained in these studies, which are presented in detail here, suggest that the chi-square ratio test in itself is not sufficient to determine equivalence of particle size distributions. This article, therefore, introduces the proposal to combine the chi-square ratio test with a test for impactor-sized mass based on Population Bioequivalence and describes methods for evaluating discrimination capabilities of the combined test. The approaches and results described in this article elucidate some of the capabilities and limitations of the original chi-square ratio test and provide rationale for development of additional tests capable of comparing APSD profiles of pharmaceutical aerosols.

Product Quality Research Institute evaluation of cascade impactor profiles of pharmaceutical aerosols, part 1: background for a statistical method.

The purpose of this article is 2-fold: (1) to document in the public domain the considerations that led to the development of a regulatory statistical test for comparison of aerodynamic particle size distribution (APSD) of aerosolized drug formulations, which was proposed in a US Food and Drug Administration (FDA) draft guidance for industry; and (2) to explain the background and process for evaluation of that test through a working group involving scientists from the FDA, industry, academia, and the US Pharmacopeia, under the umbrella of the Product Quality Research Institute (PQRI). The article and the referenced additional statistical information posted on the PQRI Web site explain the reasoning and methods used in the development of the APSD test, which is one of the key tests required for demonstrating in vitro equivalence of orally inhaled and nasal aerosol drug products. The article also describes the process by which stakeholders with different perspectives have worked collaboratively to evaluate properties of the test by drawing on statistical models, historical and practical information, and scientific reasoning. Overall, this article provides background information to accompany the companion article's discussion of the study's methods and results.

Product Quality Research Institute evaluation of cascade impactor profiles of pharmaceutical aerosols. Part 3. Final report on a statistical procedure for determining equivalence.

The purpose of this article is to report final results of the evaluation of a chi-square ratio test proposed by the US Food and Drug Administration (FDA) for demonstrating equivalence of aerodynamic particle size distribution (APSD) profiles of nasal and orally inhaled drug products. A working group of the Product Quality Research Institute previously published results demonstrating some limitations of the proposed test. In an effort to overcome the test's limited discrimination, the group proposed a supplemental test, a population bioequivalence (PBE) test for impactor-sized mass (ISM). In this final report the group compares the chi-square ratio test to the ISM-PBE test and to the combination of both tests. The basis for comparison is a set of 55 realistic scenarios of cascade impactor data, which were evaluated for equivalence by the statistical tests and independently by the group members. In many instances, the combined application of these 2 tests appeared to increase the discriminating ability of the statistical procedure compared with the chi-square ratio test alone. In certain situations the chi-square ratio test alone was sufficient to determine equivalence of APSD profiles, while in other situations neither of the tests alone nor their combination was adequate. This report describes all of these scenarios and results. In the end, the group did not recommend a statistical test for APSD profile equivalence. The group did not investigate other in vitro tests, in vivo issues, or other statistical tests for APSD profile comparisons. The studied tests are not intended for routine quality control of APSD.

Scientific Rationale for Determining the Bioequivalence of Inhaled Drugs.

In recent years, pathways for the development and approval of bioequivalent inhaled products have been established for regulated markets, including the European Union (EU), and a number of orally inhaled products (OIPs) have been approved in the EU solely on the basis of in vitro and pharmacokinetic data. This review describes how these development pathways are structured and their implications for the treatment of airway diseases such as asthma. The EU guidance follows a stepwise approach that includes in vitro criteria as the first step. If all in vitro criteria are not met, the second step is based on pharmacokinetic evaluations, which include assessments of lung and systemic bioavailability. If all pharmacokinetic criteria are not met, the third step is based on clinical endpoint studies. In this review, the scientific rationale of the European Medicines Agency guidance for the development of bioequivalent OIPs is reviewed with the focus on the development of bioequivalent OIPs in the EU. Indeed, we discuss the advantages and disadvantages of the weight-of-evidence and stepwise approaches. The evidence indicates that the EU guidance is robust and, unlike clinical endpoint studies, the pharmacokinetic studies are far more sensitive to measure the minor differences, i.e. deposition and absorption rates, in drug delivery from the test and reference products and, thus, should be best suited for assessing bioequivalence. The acceptance range of the 90% confidence intervals for pharmacokinetic bioequivalence (i.e. 80-125% for both the area under the plasma concentration-time curve and maximum plasma concentration) represent appropriately conservative margins for ensuring equivalent safety and efficacy of the test and reference products.

Equivalence considerations for orally inhaled products for local action-ISAM/IPAC-RS European Workshop report.

The purpose of this article is to document the discussions at the 2010 European Workshop on Equivalence Determinations for Orally Inhaled Drugs for Local Action, cohosted by the International Society for Aerosols in Medicine (ISAM) and the International Pharmaceutical Consortium on Regulation and Science (IPAC-RS). The article summarizes current regulatory approaches in Europe, the United States, and Canada, and presents points of consensus as well as ongoing debate in the four major areas: in vitro testing, pharmacokinetic and pharmacodynamic studies, and device similarity. Specific issues in need of further research and discussion are also identified.

Role of pharmacokinetics in establishing bioequivalence for orally inhaled drug products: workshop summary report.

In April 2010 a workshop on the "Role of Pharmacokinetics in Establishing Bioequivalence for Orally Inhaled Drug Products" was sponsored by the Product Quality Research Institute (PQRI) in coordination with Respiratory Drug Delivery (RDD) 2010. The objective of the workshop was to evaluate the current state of knowledge and identify gaps in information relating to the potential use of pharmacokinetics (PK) as the key indicator of in vivo bioequivalence (BE) of locally acting orally inhaled products (OIPs). In addition, the strengths and limitations of the PK approach to detect differences in product performance compared with in vitro and pharmacodynamic (PD)/clinical/therapeutic equivalence (TE) studies were discussed. The workshop discussed the relationship between PK and lung deposition, in vitro assessment, and PD studies and examined potential PK study designs that could serve as pivotal BE studies. It has been recognized that the sensitivity to detect differences in product performance generally decreases as one moves from in vitro testing to PD measurements. The greatest challenge in the use of PD measurements with some OIPs (particularly inhaled corticosteroids) is the demonstration of a dose-response relationship (for local effects), without which the bioassay, and hence a PD study, may not have sufficient sensitivity to detect differences in product performance. European authorities allow demonstration of in vivo BE of OIPs based solely on pharmacokinetic studies. This workshop demonstrated broader interest among discipline experts and regulators to explore approaches for the use of PK data as the key determinant of in vivo equivalence of locally acting OIPs. If accepted, the suggested approach (PK alone or in conjunction with in vitro tests) could potentially be applied to demonstrate BE of certain orally inhaled drugs.

Demonstrating Bioequivalence of Locally Acting Orally Inhaled Drug Products (OIPs): Workshop Summary Report.

This March 2009 Workshop Summary Report was sponsored by Product Quality Research Institute (PQRI) based on a proposal by the Inhalation and Nasal Technology Focus Group (INTFG) of the American Association of Pharmaceutical Scientists (AAPS). Participants from the pharmaceutical industry, academia and regulatory bodies from the United States, Europe, India, and Brazil attended the workshop with the objective of presenting, reviewing, and discussing recommendations for demonstrating bioequivalence (BE) that may be considered in the development of orally inhaled drug products and regulatory guidances for new drug applications (NDAs), abbreviated NDAs (ANDAs), and postapproval changes. The workshop addressed areas related to in vitro approaches to demonstrating BE, biomarker strategies, imaging techniques, in vivo approaches to establishing local delivery equivalence and device design similarity. The workshop presented material that provided a baseline for the current understanding of orally inhaled drug products (OIPs) and identified gaps in knowledge and consensus that, if answered, might allow the design of a robust, streamlined method for the BE assessment of locally acting inhalation drugs. These included the following: (1) cascade impactor (CI) studies are not a good 2 predictor of the pulmonary dose; more detailed studies on in vitro/in vivo correlations (e.g., suitability of CI studies for assessing differences in the regional deposition) are needed; (2) there is a lack of consensus on the appropriate statistical methods for assessing in vitro results; (3) fully validated and standardized imaging methods, while capable of providing information on pulmonary dose and regional deposition, might not be applicable to the BE of inhaled products mainly due to the problems of having access to radiolabeled innovator product; (4) if alternatives to current methods for establishing local delivery BE of OIPs cannot be established, biomarkers (pharmacodynamic or clinical endpoints) with a sufficiently steep dose-response need to be identified and validated for all relevant drug classes; and (5) the utility of pharmacokinetic studies for evaluating "local pulmonary delivery" equivalence deserves more attention. A summary of action items for seminars and working groups to address these topics in the future is also presented.

A methacholine challenge dose-response study for development of a pharmacodynamic bioequivalence methodology for albuterol metered- dose inhalers.

BACKGROUND: With the expiration of the patent on albuterol metered-dose inhalers (MDIs) in 1989, methods to assess in vivo bioequivalence of generic formulations required investigation. OBJECTIVE: In an effort to develop a sensitive method to document bioequivalence, bronchoprovocation with methacholine chloride was used to assess the dose-response relationship of albuterol as delivered by MDI. Sensitivity was assessed in terms of magnitudes of ED(50), the estimated albuterol dose required to achieve 50 % of the fitted maximal value of the pharmacodynamic effect above baseline, and change in response as a function of dose, with emphasis on 1 and 2 actuations. METHODS: On separate study days, 15 nonsmokers with mild asthma received randomized nominal albuterol doses of 0 to 576 microg by using specially manufactured MDI canisters. FEV(1) was measured 15 minutes after MDI dosing. Serially increasing doses of methacholine were administered, and FEV(1) was measured after each methacholine dose until a 20 % decrease in FEV(1) (PD(20)) was achieved. RESULTS: Mean PD(20) values after use of each of the albuterol-containing MDIs were significantly greater than either mean screening or mean placebo PD(20) values (P <.05). Mean responses and most individual subject responses to 1 and 2 actuations (90 and 180 microg) of albuterol MDI were within the sensitive region of the dose- response curve. The mean estimated ED(50) value on the basis of nonlinear mixed effect modeling was 119.2 microg (range, 33.3-337.1 microg), with an intersubject percentage coefficient of variation of 69.0 %. CONCLUSIONS: The methacholine bronchoprovocation model is safe and useful in the study of albuterol MDI dose-response in asthmatic subjects. Bronchoprovocation studies may be used for determination of bioequivalence of multisource albuterol MDI products.