Developing Clinically Relevant Dissolution Specifications for Oral Drug Products-Industrial and Regulatory Perspectives

Experiences and initiatives on pharmacokinetic modeling and simulation data analysis: Perspectives from the Brazilian Health Regulatory Agency (ANVISA)

The landscape of drug product development and regulatory sciences is evolving, driven by the increasing application of systems thinking and modeling and simulation (M&S) techniques, especially from a biopharmaceutics perspective. Patient-centric quality standards can be achieved within this context through the application of quality by design (QbD) principles and M&S, specifically by defining clinically relevant dissolution specifications (CRDS). To this end, it is essential to bridge in vitro results to drug product in vivo performance, emphasizing the need to explore the translational capacity of biopharmaceutics tools. Physiologically based M&S analyses offer a unique avenue for integrating the drug, drug product, and biological properties of a target organism to study their interactions on the pharmacokinetic response. Accordingly, Physiologically Based Biopharmaceutics Modeling (PBBM) has seen increasing use to support drug development and regulatory applications globally. In Brazil, a Model-Informed Drug Development (MIDD) policy and strategic project are not yet established, limiting applicability of M&S techniques. Drawing from the experience of the ANVISA-Academia PBBM Working Group (WG), this article assesses the opportunities and challenges for pharmacometrics (PMx) in Brazil and proposes strategies to advance the adoption of M&S analyses into regulatory decision-making.

Justification of widened dissolution specifications of an extended-release product using physiologically based biopharmaceutics modeling

Drug products meeting the dissolution specifications is crucial in order to ensure consistent clinical performance. However, in certain cases, wider dissolution specifications may be required based on product behaviour. While the justification of such wider specifications may be challenging from a regulatory context, approaches such as physiological-based biopharmaceutics modeling (PBBM) can be utilised for this purpose.Product DRL is a fixed-dose combination product consisting of immediate release (IR) and extended-release (ER) portions. For the ER portion, the dissolution specifications consisted of four time points, and a proposal was made to relax the specification at the 2h time point (from 50-70% to 45-67%) to reduce the batch failures at the commercial scale.To support the wider specification, a PBBM was developed and extensively validated with literature & in-house studies. Virtual bioequivalence was performed using the pivotal clinical study data.Virtual dissolution profiles for proposed wider specifications were generated using three different approaches. The incorporation of lower and upper dissolution profiles into the model indicated the absence of impact on in vivo performance thereby justifying the specifications.Regulatory acceptance of proposed specifications with PBBM indicated the significance of using modeling approaches to reduce repeated testing thereby facilitating faster approvals.

Establishing Virtual Bioequivalence and Clinically Relevant Specifications for Omeprazole Enteric-Coated Capsules by Incorporating Dissolution Data in PBPK Modeling

Currently, Biopharmaceutics Classification System (BCS) classes I and III are the only biological exemptions of immediate-release solid oral dosage forms eligible for regulatory approval. However, through virtual bioequivalence (VBE) studies, BCS class II drugs may qualify for biological exemptions if reliable and validated modeling is used. Here, we sought to establish physiologically based pharmacokinetic (PBPK) models, in vitro-in vivo relationship (IVIVR), and VBE models for enteric-coated omeprazole capsules, to establish a clinically-relevant dissolution specification (CRDS) for screening BE and non-BE batches, and to ultimately develop evaluation criteria for generic omeprazole enteric-coated capsules. To establish omeprazole's IVIVR based on the PBPK model, we explored its in vitro dissolution conditions and then combined in vitro dissolution profile studies with in vivo clinical trials. The predicted omeprazole pharmacokinetics (PK) profiles and parameters closely matched the observed PK data. Based on the VBE results, the bioequivalence study of omeprazole enteric-coated capsules required at least 48 healthy Chinese subjects. Based on the CRDS, the capsules' in vitro dissolution should not be < 28%-54%, < 52%, or < 80% after two, three, and six hours, respectively. Failure to meet these dissolution criteria may result in non-bioequivalence. Here, PBPK modeling and IVIVR methods were used to bridge the in vitro dissolution of the drug with in vivo PK to establish the BE safety space of omeprazole enteric-coated capsules. The strategy used in this study can be applied in BE studies of other BCS II generics to obtain biological exemptions and accelerate drug development.

Applications of Modeling and Simulation Approaches in Support of Drug Product Development of Oral Dosage Forms and Locally Acting Drug Products: a Symposium Summary

The number of modeling and simulation applications, including physiologically based pharmacokinetic (PBPK) models, physiologically based biopharmaceutics modeling (PBBM), and empirical models, has been constantly increasing along with the regulatory acceptance of these methodologies. While aiming at minimizing unnecessary human testing, these methodologies are used today to support the development and approval of novel drug products and generics. Modeling approaches are leveraged today for assessing drug-drug interaction, informing dose adjustments in renally or hepatically impaired patients, perform dose selection in pediatrics and pregnant women and diseased populations, and conduct biopharmaceutics-related assessments such as establish clinically relevant specifications for drug products and achieve quality assurance throughout the product life cycle. In the generics space, PBPK analyses are utilized toward virtual bioequivalence assessments within the scope of alternative bioequivalence approaches, product-specific guidance development, and food effect assessments among others. Case studies highlighting the evolving and expanding role of modeling and simulation approaches within the biopharmaceutics space were presented at the symposium titled "Model Informed Drug Development (MIDD): Role in Dose Selection, Vulnerable Populations, and Biowaivers - Chemical Entities" and Prologue "PBPK/PBBM to inform the Bioequivalence Safe Space, Food Effects, and pH-mediated DDIs" at the American Association of Pharmaceutical Scientists (AAPS) PharmSci 360 Annual Meeting in Boston, MA, on October 16-19, 2022, and are summarized here.

Biopharmaceutics Risk Assessment-Connecting Critical Bioavailability Attributes with In Vitro, In Vivo Properties and Physiologically Based Biopharmaceutics Modeling to Enable Generic Regulatory Submissions

Quality risk assessment following ICH Q9 principles is an important activity to ensure optimal clinical efficacy and safety of a drug product. Typically, risk assessment is focused on product performance wherein critical material attributes, formulation variables, and process parameters are evaluated from a manufacturing perspective. Extending ICH Q9 principles to biopharmaceutics risk assessment to identify factors that can impact in vivo performance is an upcoming area. This is evident by recent regulatory trends wherein a new term critical bioavailability attributes (CBA) has been coined to identify such factors. Although significant work has been performed for biopharmaceutics risk assessment for new molecules, there is a need for harmonized biopharmaceutics risk assessment workflow for generic submissions. In this manuscript, we attempted to provide a framework for performing biopharmaceutics risk assessment for generic regulatory submissions. A detailed workflow for performing biopharmaceutics risk assessment includes identification of initial CBA (iCBA), their confirmatory evaluation followed by definition of the control strategy. Tools for biopharmaceutics risk assessment, i.e., bio-discriminatory dissolution method and physiologically based biopharmaceutics modeling (PBBM) were discussed from a practical perspective. Furthermore, a case study for CBA evaluation using PBBM modeling for an extended-release product for regulatory submission has been described using the proposed workflow. Finally, future directions of integrating CBA evaluation, biopharmaceutics risk assessment to the FDA Knowledge Aided Structured Assessment (KASA) initiative, the necessity of risk assessment templates, and knowledge sharing between industry and academia are discussed. Overall, the work described in this manuscript can facilitate and provide guidance for biopharmaceutics risk assessment for generic submissions.

Best Practices for Integration of Dissolution Data into Physiologically Based Biopharmaceutics Models (PBBM): A Biopharmaceutics Modeling Scientist Perspective

Dissolution is considered as a critical input into physiologically based biopharmaceutics models (PBBM) as it governs in vivo exposure. Despite many workshops, initiatives by academia, industry, and regulatory, wider practices are followed for dissolution data input into PBBM models. Due to variety of options available for dissolution data input into PBBM models, it is important to understand pros, cons, and best practices while using specific dissolution model. This present article attempts to summarize current understanding of various dissolution models and data inputs in PBBM software's and aims to discuss practical challenges and ways to overcome such scenarios. Different approaches to incorporate dissolution data for immediate, modified, and delayed release formulations are discussed in detail. Common challenges faced during fitting of z-factor are discussed along with novel approach of dissolution data incorporation using P-PSD model. Ways to incorporate dissolution data for MR formulations using Weibull and IVIVR approaches were portrayed with examples. Strategies to incorporate dissolution data for DR formulations was depicted along with practical aspects. Approaches to generate virtual dissolution profiles, using Weibull function, DDDPlus, and time scaling for defining dissolution safe space, and strategies to generate virtual dissolution profiles for justifying single and multiple dissolution specifications were discussed. Finally, novel ways to integrate dissolution data for complex products such as liposomes, data from complex dissolution systems, importance of precipitation, and bio-predictive ability of QC media for evaluation of CBA's impact were discussed. Overall, this article aims to provide an easy guide for biopharmaceutics modeling scientist to integrate dissolution data effectively into PBBM models.

Current State and Challenges of Physiologically Based Biopharmaceutics Modeling (PBBM) in Oral Drug Product Development

Physiologically based biopharmaceutics modeling (PBBM) emphasizes the integration of physicochemical properties of drug substance and formulation characteristics with system physiological parameters to predict the absorption and pharmacokinetics (PK) of a drug product. PBBM has been successfully utilized in drug development from discovery to postapproval stages and covers a variety of applications. The use of PBBM facilitates drug development and can reduce the number of preclinical and clinical studies. In this review, we summarized the major applications of PBBM, which are classified into six categories: formulation selection and development, biopredictive dissolution method development, biopharmaceutics risk assessment, clinically relevant specification settings, food effect evaluation and pH-dependent drug-drug-interaction risk assessment. The current state of PBBM applications is illustrated with examples from published studies for each category of application. Despite the variety of PBBM applications, there are still many hurdles limiting the use of PBBM in drug development, that are associated with the complexity of gastrointestinal and human physiology, the knowledge gap between the in vitro and the in vivo behavior of drug products, the limitations of model interfaces, and the lack of agreed model validation criteria, among other issues. The challenges and essential considerations related to the use of PBBM are discussed in a question-based format along with the scientific thinking on future research directions. We hope this review can foster open discussions between the pharmaceutical industry and regulatory agencies and encourage collaborative research to fill the gaps, with the ultimate goal to maximize the applications of PBBM in oral drug product development.

Multi-phase multi-layer mechanistic dermal absorption (MPML MechDermA) model to predict local and systemic exposure of drug products applied on skin

Physiologically-based pharmacokinetic models combine knowledge about physiology, drug product properties, such as physicochemical parameters, absorption, distribution, metabolism, excretion characteristics, formulation attributes, and trial design or dosing regimen to mechanistically simulate drug pharmacokinetics (PK). The current work describes the development of a multiphase, multilayer mechanistic dermal absorption (MPML MechDermA) model within the Simcyp Simulator capable of simulating uptake and permeation of drugs through human skin following application of drug products to the skin. The model was designed to account for formulation characteristics as well as body site- and sex- population variability to predict local and systemic bioavailability. The present report outlines the structure and assumptions of the MPML MechDermA model and includes results from simulations comparing absorption at multiple body sites for two compounds, caffeine and benzoic acid, formulated as solutions. Finally, a model of the Feldene (piroxicam) topical gel, 0.5% was developed and assessed for its ability to predict both plasma and local skin concentrations when compared to in vivo PK data.

Developing Clinically Relevant Dissolution Specifications (CRDSs) for Oral Drug Products: Virtual Webinar Series

A webinar series that was organised by the Academy of Pharmaceutical Sciences Biopharmaceutics focus group in 2021 focused on the challenges of developing clinically relevant dissolution specifications (CRDSs) for oral drug products. Industrial scientists, together with regulatory and academic scientists, came together through a series of six webinars, to discuss progress in the field, emerging trends, and areas for continued collaboration and harmonisation. Each webinar also hosted a Q&A session where participants could discuss the shared topic and information. Although it was clear from the presentations and Q&A sessions that we continue to make progress in the field of CRDSs and the utility/success of PBBM, there is also a need to continue the momentum and dialogue between the industry and regulators. Five key areas were identified which require further discussion and harmonisation.

Physiologically based pharmacokinetic modeling and simulations to inform dissolution specifications and clinical relevance of release rates on elagolix exposure

The aim of this analysis was to use a physiologically based pharmacokinetic (PBPK) model to predict the impact of changes in dissolution rates on elagolix exposures and define clinically relevant acceptance criteria for dissolution. Varying in vitro dissolution profiles were utilized in a PBPK model to describe the absorption profiles of elagolix formulations used in Phase 3 clinical trials and for the to be marketed commercial formulations. Single dose studies of 200 mg elagolix formulations were used for model verification under fasted conditions. Additional dissolution scenarios were evaluated to assess the impact of dissolution rates on elagolix exposures. Compared to the Phase 3 clinical trial formulation, sensitivity analysis on dissolution rates suggested that a hypothetical scenario of ∼75% slower dissolution rate would result in 14% lower predicted elagolix plasma exposures, however, the predicted exposures are still within the bioequivalence boundaries of 0.8-1.25 for both C_max and AUC. A clinically verified PBPK model of elagolix was utilized to evaluate the impact of wider dissolution specifications on elagolix plasma exposures. The simulation results indicated that a slower in vitro dissolution profile, would not have a clinically significant impact on elagolix exposures. These model results informed the setting of wider dissolution specifications without requiring in vivo studies.

Physiologically Based Biopharmaceutics Model of Vildagliptin Modified Release (MR) Tablets to Predict In Vivo Performance and Establish Clinically Relevant Dissolution Specifications

The objective of the study was to predict pharmacokinetic (PK) and pharmacodynamic (PD) parameters of matrix-based modified release (MR) drug product of vildagliptin. Physiologically based biopharmaceutics modeling (PBBM) was developed using GastroPlus™ based on the available data including immediate-release (IR) drug product of vildagliptin. In vitro-in vivo correlation (IVIVC) was developed using mechanistic deconvolution to predict plasma concentration-time profile and PK parameters for a MR drug product planned for clinical use. Both methods, i.e., PBBM and IVIVC, were compared for the predicted PK parameters. Integration of DDDPlus™ and GastroPlus™ modeling was performed to explore clinically relevant dissolution specifications for vildagliptin MR tablets. The bioequivalence (BE) between batches with different dissolution specifications was evaluated using virtual clinical trials. The PD effect of dipeptidyl peptidase-IV (DPP-IV) inhibition was simulated utilizing PDPlus™ model in GastroPlus™. The results indicated that IVIVC best correlated the simulated PK parameters with those observed with the clinical study. The outcomes highlight the importance of integration of in vitro and in silico tools towards predictability of PK and PD parameters for a MR drug product. However, the post absorptive phase was found to be more dependent on the demographics of the healthy subjects.

Development of In Vitro Dissolution Testing Methods to Simulate Fed Conditions for Immediate Release Solid Oral Dosage Forms

In vitro dissolution testing is widely used to mimic and predict in vivo performance of oral drug products in the gastrointestinal (GI) tract. This literature review assesses the current in vitro dissolution methodologies being employed to simulate and predict in vivo drug dissolution under fasted and fed conditions, with emphasis on immediate release (IR) solid oral dosage forms. Notable human GI physiological conditions under fasted and fed states have been reviewed and summarized. Literature results showed that dissolution media, mechanical forces, and transit times are key dissolution test parameters for simulating specific postprandial conditions. A number of biorelevant systems, including the fed stomach model (FSM), GastroDuo device, dynamic gastric model (DGM), simulated gastrointestinal tract models (TIM), and the human gastric simulator (HGS), have been developed to mimic the postprandial state of the stomach. While these models have assisted in expanding physiological relevance of in vitro dissolution tests, in general, these models lack the ability to fully replicate physiological conditions/processes. Furthermore, the translatability of in vitro data to an in vivo system remains challenging. Additionally, physiologically based pharmacokinetic (PBPK) modeling has been employed to evaluate the effect of food on drug bioavailability and bioequivalence. Here, we assess the current status of in vitro dissolution methodologies and absorption PBPK modeling approaches to identify knowledge gaps and facilitate further development of in vitro dissolution methods that factor in fasted and fed states. Prediction of in vivo drug performance under fasted and fed conditions via in vitro dissolution testing and modeling may potentially help efforts in harmonizing global regulatory recommendations regarding in vivo fasted and fed bioequivalence studies for solid oral IR products.

Utility of Modeling and Simulation Approach to Support the Clinical Relevance of Dissolution Specifications: a Case Study from Upadacitinib Development

Dissolution specifications are often essential in assuring the quality and consistency of therapeutic benefits of drug lots released to the market as in vitro dissolution is often considered to be a surrogate for bioavailability. Despite the importance of demonstrating the clinical relevance of the dissolution specifications, it is often challenging to achieve this goal. In this case study, a modeling and simulation approach was utilized to support the clinical relevance of the dissolution specifications for upadacitinib extended-release tablets. A level A in vitro in vivo correlation was developed and utilized in predicting upadacitinib plasma exposures for formulations which correspond to the upper and lower dissolution limits. Exposure-response models for upadacitinib efficacy and safety in patients with moderate to severe rheumatoid arthritis (RA) were utilized to conduct clinical trial simulations to evaluate the efficacy and safety of formulations at the upper and lower dissolution boundaries. Each simulated clinical trial consisted of three treatment arms: (1) upadacitinib 15 mg QD using the target formulation, (2) upadacitinib 15 mg QD using a formulation at the lower dissolution boundary, and (3) upadacitinib 15 mg QD using a formulation at the upper dissolution boundary. Each simulated trial included 300 patients per arm and simulations were replicated 200 times. Results demonstrated that formulations at the lower and upper dissolution boundaries are predicted to have noninferior efficacy and comparable safety to the target 15 mg extended-release formulation. This approach was successfully utilized in demonstrating the clinical relevance of upadacitinib extended-release tablet dissolution specifications. Graphical Abstract.

A Novel Approach to Justify Dissolution Differences in an Extended Release Drug Product Using Physiologically Based Biopharmaceutics Modeling and Simulation

Dr Reddy's Laboratories Ltd. developed generic version of XYZ extended release tablets (ER) and achieved bioequivalence as per criteria mentioned by USFDA in both fasting and fed conditions for higher strength formulation (1200 mg). However, on comparison of multimedia dissolution profiles in pH 4.5 acetate media, the f2 similarity value was <50. The lower strength formulation (600 mg) demonstrated faster dissolution profile. This was identified as strength-dependent sink condition difference and in vitro multiunit dissolution studies were used to justify sink differences between the higher and lower strengths. Additionally, a Physiologically Based Biopharmaceutics Model (PBBM) was developed using GastroPlus^TM. The validity of this model was established using in-house human pharmacokinetic data. Further, this model was used to justify the insignificant in vivo impact of the faster dissolution profile for the lower strength formulation. This work provides a novel and less explored approach that can be used to obtain biowaiver for lower strength formulations when the standard biowaiver criteria cannot be met. This work also demonstrates the usefulness of PBBM to justify dissolution dissimilarity between dose proportional formulations and to evaluate its biopharmaceutics risk without the need for actual in vivo studies.

Physiologically Based Biopharmaceutics Modeling to Demonstrate Virtual Bioequivalence and Bioequivalence Safe-space for Ribociclib which has Permeation Rate-controlled Absorption

A physiologically based biopharmaceutics model (PBBM) was developed to support formulation development of ribociclib, an orally bioavailable selective CDK4/6 inhibitor. Ribociclib is a weak base with moderate permeability and complete in vitro dissolution under stomach pH. GastroPlus™ was used to simulate the pharmacokinetics (PK) in healthy volunteers after capsule dosing. Simulations showed rapid, complete dissolution in human stomach without intestinal precipitation and with permeation-controlled absorption. Permeability was identified as controlling the systemic exposure. PBBM predicted bioequivalence (BE) between capsule and tablet in healthy volunteers, despite non-similarity between in vitro dissolution kinetics (f2<50). BE was verified in a clinical study. Then virtual bioequivalence (VBE) simulations predicted comparable PK in cancer patients between capsule and tablet of commercial batch, which was also confirmed in a clinical study. Finally, virtual trial simulations using virtual batches with slower dissolution were used to define an in vitro BE safe-space for tablets, where BE is expected. PBBM can identify drugs with permeability-controlled absorption for which formulation optimization can focus more on manufacturability rather than dissolution. PBBM can be used to predict BE study outcomes, define clinically relevant specification and BE safe-space, superseding dissolution similarity f2 criteria.

Establishing the Bioequivalence Safe Space for Immediate-Release Oral Dosage Forms using Physiologically Based Biopharmaceutics Modeling (PBBM): Case Studies

For oral drug products, in vitro dissolution is the most used surrogate of in vivo dissolution and absorption. In the context of drug product quality, safe space is defined as the boundaries of in vitro dissolution, and relevant quality attributes, within which drug product variants are expected to be bioequivalent to each other. It would be highly desirable if the safe space could be established via a direct link between available in vitro data and in vivo pharmacokinetics. In response to the challenges with establishing in vitro-in vivo correlations (IVIVC) with traditional modeling approaches, physiologically based biopharmaceutics modeling (PBBM) has been gaining increased attention. In this manuscript we report five case studies on using PBBM to establish a safe space for BCS Class 2 and 4 across different companies, including applications in an industrial setting for both internal decision making or regulatory applications. The case studies provide an opportunity to reflect on practical vs. ideal datasets for safe space development, the methodologies for incorporating dissolution data in the model and the criteria used for model validation and application. PBBM and safe space, still represent an evolving field and more examples are needed to drive development of best practices.

Physiologically-Based Pharmacokinetic Modeling to Support Determination of Bioequivalence for Dermatological Drug Products: Scientific and Regulatory Considerations

Physiologically-based pharmacokinetic (PBPK) modeling and simulation provides mechanism-based predictions of the pharmacokinetics of an active ingredient following its administration in humans. Dermal PBPK models describe the skin permeation and disposition of the active ingredient following the application of a dermatological product on the skin of virtual healthy and diseased human subjects. These models take into account information on product quality attributes, physicochemical properties of the active ingredient and skin (patho)physiology, and their interplay with each other. Regulatory and product development decision makers can leverage these quantitative tools to identify factors impacting local and systemic exposure. In the realm of generic drug products, the number of US Food and Drug Administratioin (FDA) interactions that use dermal PBPK modeling to support alternative bioequivalence (BE) approaches is increasing. In this report, we share scientific considerations on the development, verification and validation (V&V), and application of PBPK models within the context of a virtual BE assessment for dermatological drug products. We discuss the challenges associated with model V&V for these drug products stemming from the fact that target-site active ingredient concentrations are typically not measurable. Additionally, there are no established relationships between local and systemic PK profiles, when the latter are quantifiable. To that end, we detail a multilevel model V&V approach involving validation for the model of the drug product of interest coupled with the overall assessment of the modeling platform in use while leveraging in vitro and in vivo data related to local and systemic bioavailability.

Development, validation and application of physiologically based biopharmaceutics model to justify the change in dissolution specifications for DRL ABC extended release tablets

OBJECTIVE

The generic drug product DRL ABC is an Extended Release (ER) Tablet manufactured by Dr. Reddy's Laboratories Limited and have multi point dissolution as part of release specification. A proposal is being made to revise the dissolution specification and the aim of present work was to evaluate if this would still provide bioequivalent product.

METHODS

PBBM was developed for DRL ABC using literature reported pharmacokinetic (PK) data. The intravenous PK data and in vitro metabolic rate constants were utilized for developing PBPK model first, followed by that in conjugation with mechanistic ACAT^TM model, a PBBM is developed for per-oral immediate release formulations. The validated model was applied to predict clinical bioequivalence (BE) study data for the Reference (Innovator ER Tablet) and Test product. For Reference and Test product, in vivo dissolution profiles were mechanistically deconvoluted from plasma concentration (Cp)-time profiles. Further, mechanistic in vitro-in vivo relationship (IVIVR) applied to in vitro release profiles of two hypothetical Test product batches (one with single point low dissolution profile (SPLP) and other with overall low dissolution profile (LP)) in order to calculate their in vivo releases and population simulation was performed with 40 virtual subjects.

RESULTS

Results from the cross-over virtual trials showed BE between the Reference and various Test product batches (SPLP and LP), with maximum Cp (C_max) and area under the Cp-time curve (AUC_0-inf) well within 80-125% range.

CONCLUSION

PBBM in conjugation with IVIVR and virtual BE was successfully applied for justifying changes in dissolution specification of DRL ABC.

Physiologically-based pharmacokinetic modeling to support bioequivalence and approval of generic products: A case for diclofenac sodium topical gel, 1

Establishing bioequivalence (BE) for dermatological drug products by conducting comparative clinical end point studies can be costly and the studies may not be sufficiently sensitive to detect certain formulation differences. Quantitative methods and modeling, such as physiologically‐based pharmacokinetic (PBPK) modeling, can support alternative BE approaches with reduced or no human testing. To enable PBPK modeling for regulatory decision making, models should be sufficiently verified and validated (V&V) for the intended purpose. This report illustrates the US Food and Drug Administration (FDA) approval of a generic diclofenac sodium topical gel that was based on a totality of evidence, including qualitative and quantitative sameness and physical and structural similarity to the reference product, an in vivo BE study with PK end points, and, more importantly, for the purposes of this report, a virtual BE assessment leveraging dermal PBPK modeling and simulation instead of a comparative clinical end point study in patients. The modeling approach characterized the relationship between systemic (plasma) and local (skin and synovial fluid) diclofenac exposure and demonstrated BE between the generic and reference products at the presumed site of action. Based on the fit‐for‐purpose modeling principle, the V&V process involved assessing observed data of diclofenac concentrations in skin tissues and plasma, and the overall performance of the modeling platform for relevant products. Using this case as an example, this report provides current scientific considerations on good practices for model V&V and the establishment of BE for dermatological drug products when leveraging PBPK modeling and simulation for regulatory decision making.

Potential Application of USP Paddle and Basket Dissolution Methods in Discriminating for Portioned Moist Snuff and Snus Smokeless Tobacco Products

The focus of the study was to develop discriminatory dissolution methods for portioned snus and moist snuff sub-categories of smokeless tobacco products (STPs) using USP basket and paddle apparatuses. Skoal Classic Wintergreen (SCW) and CORESTA CRP1.1 pouches were used as test products. The dissolution was performed at 10, 20, 30, 40, and 50 rpm basket or paddle speed in 500 ml artificial saliva pH 6.8. The products were also characterized for assay, pH, particle size, and loss on drying. The dissolution profiles were evaluated for amount/% of nicotine dissolved, time to reach plateau, and profiles comparison by f2 and f1 factors. The nicotine assay was 13.3 ± 0.2 and 7.6 ± 0.1 mg/pouch for SCW and CRP1.1, respectively. The nicotine dissolved in 30 min from SCW and CRP1.1 were 38.4-81.8 and 37.6-88.1, and 50.5-64.9 and 72.3-92.1% by paddle and basket methods, respectively. The f2 and f1 values were ≤ 39.2 and ≥ 42.1 and ≤ 43.2 and ≥ 34.1 for basket methods and paddle methods. RSD were less than 20% at all points of dissolution profiles, and dissolution plateau were achieved in 30 min at some of the tested conditions. In summary, dissolution methods based on basket and paddle can be used as a performance test for STPs.

Physiologically Based Pharmacokinetic/Pharmacodynamic Modeling to Support Waivers of In Vivo Clinical Studies: Current Status, Challenges, and Opportunities

Physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) modeling has been extensively applied to quantitatively translate in vitro data, predict the in vivo performance, and ultimately support waivers of in vivo clinical studies. In the area of biopharmaceutics and within the context of model-informed drug discovery and development (MID3), there is a rapidly growing interest in applying verified and validated mechanistic PBPK models to waive in vivo clinical studies. However, the regulatory acceptance of PBPK analyses for biopharmaceutics and oral drug absorption applications, which is also referred to variously as "PBPK absorption modeling" [Zhang et al. CPT: Pharmacometrics Syst. Pharmacol. 2017, 6, 492], "physiologically based absorption modeling", or "physiologically based biopharmaceutics modeling" (PBBM), remains rather low [Kesisoglou et al. J. Pharm. Sci. 2016, 105, 2723] [Heimbach et al. AAPS J. 2019, 21, 29]. Despite considerable progress in the understanding of gastrointestinal (GI) physiology, in vitro biopharmaceutic and in silico tools, PBPK models for oral absorption often suffer from an incomplete understanding of the physiology, overparameterization, and insufficient model validation and/or platform verification, all of which can represent limitations to their translatability and predictive performance. The complex interactions of drug substances and (bioenabling) formulations with the highly dynamic and heterogeneous environment of the GI tract in different age, ethnic, and genetic groups as well as disease states have not been yet fully elucidated, and they deserve further research. Along with advancements in the understanding of GI physiology and refinement of current or development of fully mechanistic in silico tools, we strongly believe that harmonization, interdisciplinary interaction, and enhancement of the translational link between in vitro, in silico, and in vivo will determine the future of PBBM. This Perspective provides an overview of the current status of PBBM, reflects on challenges and knowledge gaps, and discusses future opportunities around PBPK/PD models for oral absorption of small and large molecules to waive in vivo clinical studies.