Bioavailability and/or bioequivalence studies play a key role in the drug development period for both new drug products and their generic equivalents. For both, these studies are also important in the postapproval period in the presence of certain manufacturing changes. Like many regulatory studies, the assessment of bioavailability and bioequivalence can generally be achieved by considering the following three questions. What is the primary question of the study? What are the tests that can be used to address the question? What degree of confidence is needed for the test outcome? This article reviews the regulatory science of bioavailability and bioequivalence and provides FDA's recommendations for drug sponsors who intend to establish bioavailability and/or demonstrate bioequivalence for their pharmaceutical products during the developmental process or after approval.

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.

Good statistical agreement is obtained between the reported and measured sizes of the PS microspheres. BDP particles were clearly distinguishable from those of excipients. Raman chemical imaging (RCI) is able to differentiate between and identify the chemical makeup of multiple components in complex BDP sample and placebo mixtures. The Raman chemical imaging method (coupled Raman and optical imaging) shows promise as a method for characterizing particle size and shape of corticosteroid in aqueous nasal spray suspension formulations. However, rigorous validation of RCI for PSD analysis is incomplete and requires additional research effort. Some specific areas of concern are discussed.

Abstract. Dry powder inhalers (DPIs) are used to deliver locally acting drugs (e.g., bronchodilators and corticosteroids) for treatment of lung diseases such as asthma and chronic obstructive pulmonary disease (COPD). Demonstrating bioequivalence (BE) for DPI products is challenging, primarily due to an incomplete understanding of the relevance of drug concentrations in blood or plasma to equivalence in drug delivery to the local site(s) of action. Thus, BE of these drug/device combination products is established based on an aggregate weight of evidence, which utilizes in vitro studies to demonstrate equivalence of in vitro performance, pharmacokinetic or pharmacodynamic studies to demonstrate equivalence of systemic exposure, and pharmacodynamic and clinical endpoint studies to demonstrate equivalence in local action. This review discusses key aspects of in vitro studies in supporting the establishment of BE for generic locally acting DPI products. These aspects include comparability in device resistance and equivalence in in vitro testing for single inhalation (actuation) content and aerodynamic particle size distribution.

Abstract. This study investigated the effect of modifying the design of the Cyclohaler on its aerosolization performance and comparability to the HandiHaler at multiple flow rates. The Cyclohaler and HandiHaler were designated as model test and reference unit-dose, capsule-based dry powder inhalers (DPIs), respectively. The flow field, pressure drop, and carrier particle trajectories within the Cyclohaler and HandiHaler were modeled via computational fluid dynamics (CFD). With the goal of achieving in vitro comparability to the HandiHaler, the CFD results were used to identify key device attributes and to design two modifications of the Cyclohaler (Mod 1 and Mod 2), which matched the specific resistance of the HandiHaler but exhibited different cyclonic flow conditions in the device. Aerosolization performance of the four DPI devices was evaluated by using the reference product's capsule and formulation (Spiriva capsule) and a multistage cascade impactor. The in vitro data showed that Mod 2 provided a closer match to the HandiHaler than the Cyclohaler and Mod 1 at 20, 39, and 55 l/min. The in vitro and CFD results together suggest that matching the resistance of test and reference DPI devices is not sufficient to attain comparable aerosolization performance, and the improved in vitro comparability of Mod 2 to the HandiHaler may be related to the greater degree of similarities of the flow rate of air through the pierced capsule (Q c ) and the maximum impact velocity of representative carrier particles (V n ) in the Cyclohaler-based device. This investigation illustrates the importance of enhanced product understanding, in this case through the CFD modeling and in vitro characterization of aerosolization performance, to enable identification and modification of key design features of a test DPI device for achieving comparable aerosolization performance to the reference DPI device.KEY WORDS: computational fluid dynamics; device design; dry powder inhaler; in vitro comparability; in vitro performance.

Abstract. International regulatory agencies have developed recommendations and guidances for bioequivalence approaches of orally inhaled drug products (OIDPs) for local action. The objective of this article is to discuss the similarities and differences among these approaches used by international regulatory authorities when applications of generic and/or subsequent entry locally acting OIDPs are evaluated. We focused on four jurisdictions that currently have published related guidances for generic and/or subsequent entry OIDPs.

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.

Acceptable model fits to all individual subject dose-response data were not achieved for any dermatologic corticosteroid product. However, population dose-responses were adequately described by the Emax model. On the basis of these data, the optimal dose duration used for comparison of multisource dermatologic corticosteroid products is recommended to be equal to the ED50 based on population modeling of pilot dose-response study data.