Background:Conventional statistical analysis of clinical data based on standard methods suggests that fixed combinations of fluticasone propionate (FP) and salmeterol (SALM) inhaled via Wixela® Inhub® dry powder (test) are therapeutically and pharmacokinetically equivalent to Advair® Diskus® (reference). Assessment of bioequivalence, test/reference, based on empirical population pharmacokinetic modelling was compared with published outcomes based on a non-compartmental analysis (NCA) approach. Methods:Three inhalations of FP/SALM were administered to healthy subjects with 7-day washouts via test and reference and delivered doses of 100/50, 250/50, or 500/50 µg (total matched doses of 300/150, 750/150, or 1500/150 µg) in studies 1, 2, and 3, respectively. Empirically derived pharmacokinetic structural models, considering random effects of subject (FP, SALM) or study (SALM), emulating linear first-order input, disposition and elimination were fitted to plasma concentrations with a frequentist approach, by study/dose of FP, and across studies of SALM, using product as categorical covariate. Bioequivalence was assessed using individually predicted relative systemic extent of bioavailability (F4_rel) and ratio of individually predicted peak concentrations (Cmax). Results:The models adequately described plasma concentration versus time data. Descriptive statistics and bioequivalence assessments (90% confidence interval generally within 0.80-1.25) reflected NCA-derived outcomes. Conclusion:Model- and NCA-based approaches to assess bioequivalence were consistent. However, a frequentist parametric approach that fully utilizes the population analysis potential and mechanistically predicts regional pulmonary deposition of FP and SALM would require a demographically more heterogenous data set and analysis including additional outcomes of parenteral and oral administration to discriminate presystemic from systemic disposition.

This is the fourth paper in a series describing an inhalation biopharmaceutics classification system (iBCS), an initiative supported by the Product Quality Research Institute. The paper examines the application of the inhalation Biopharmaceutics Classification System (iBCS) through the drug discovery, development, and postapproval phases for orally inhaled drug products (OIDP) and for the development of generic OIDPs. We consider the implication of the iBCS class in terms of product performance and identify the practical gaps that must be filled to enable the classification system to be adopted into day-to-day practice. Consideration is given to the critical experimental data required and the methods for their generation with a focus on: (i) dose to the lungs, (ii) drug solubility in relevant media and methods to model the dissolution of respirable formulations, and (iii) pulmonary drug permeability. As described in three prior publications, the iBCS was developed to classify inhaled drugs based on physicochemical and biorelevant product attributes in a manner that will allow formulators and discovery chemists to identify and mitigate product development risks. It was not established to enable in vitro determination of bioequivalence between orally inhaled drug products. However, once analytical methods are in place to correctly classify inhaled drugs, the system has the potential to provide an understanding of the development risks associated with both establishing bioequivalence between two drug products and enabling postapproval changes based on product iBCS class.

Based on early reports of the efficacy of hydroxychloroquine sulfate (HCQS) to inhibit SARS-CoV-2 viral replication in vitro, and since severe pulmonary involvement is the major cause of COVID-19 mortality, we assessed the safety and efficacy of aerosolized HCQS (aHCQS) therapy in animals and humans. In a Phase 1 study of aHCQS in healthy volunteers, doses up to 50 mg were well tolerated and estimated epithelial lining fluid concentrations immediately after inhalation (>2,000 μM) exceeded the in vitro concentrations needed for suppression of viral replication (≥119 μM). A study in rats comparing HCQS solution administered orally (13.3 mg/kg) and by intratracheal installation (IT 0.18 mg/kg, <5% of oral dose) demonstrated that at 2 minutes, IT administration was associated with 5X higher mean hydroxychloroquine (HCQ) concentrations in the lung (IT: 49.5 ± 6.5 µg HCQ/g tissue, oral: 9.9 ± 3.4; p<0.01). A subsequent study of IT and intranasal HCQS in the Syrian hamster model of SARS-CoV-2 infection, however, failed to show clinical benefit. We conclude that aHCQS alone is unlikely to be effective for COVID-19, but based on our aHCQS pharmacokinetics and current viral entry data, adding oral HCQS to aHCQS, along with a transmembrane protease inhibitor, may improve efficacy.### Competing Interest StatementThis study was funded in entirety by Pulmoquine Therapeutics, Inc. San Diego, CA. O. S. Bentur and B. S. Coller are supported by grant UL1 TR001866 from the National Center for Advancing Translational Sciences, National Institutes of Health. B.S.C. and R.B.M. were founders, equity holders and advisors to Pulmoquine Therapeutics, Inc. I.G. was an equity holder in Pulmoquine therapeutics. Pulmoquine Therapeutics, Inc. was dissolved in August 2021. A.N.C., H.B., and I.G. were paid consultants for Pulmoquine Therapeutics, Inc.### Clinical TrialNCT 04461353### Funding StatementThis study was funded in entirety by Pulmoquine Therapeutics, Inc. San Diego, CA.### Author DeclarationsI confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.YesThe details of the IRB/oversight body that provided approval or exemption for the research described are given below:The Rockefeller University Institutional Review Board gave ethical approval for the human studies.I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.YesI understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).YesI have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.YesAll data produced in the present study are available upon reasonable request to the authors.

In this article, we specify for the first time a quantitative biopharmaceutics classification system for orally inhaled drugs. To date, orally inhaled drug product developers have lacked a biopharmaceutics classification system like the one developed to navigate the development of immediate release of oral medicines. Guideposts for respiratory drug discovery chemists and inhalation product formulators have been elusive and difficult to identify due to the complexity of pulmonary physiology, the intricacies of drug deposition and disposition in the lungs, and the influence of the inhalation delivery device used to deliver the drug as a respirable aerosol. The development of an inhalation biopharmaceutics classification system (iBCS) was an initiative supported by the Product Quality Research Institute (PQRI). The goal of the PQRI iBCS working group was to generate a qualitative biopharmaceutics classification system that can be utilized by inhalation scientists as a "rule of thumb" to identify desirable molecular properties and recognize and manage CMC product development risks based on physicochemical properties of the drug and the deposited lung dose. Herein, we define the iBCS classes quantitatively according to the dose number and permeability. The proposed iBCS was evaluated for its ability to categorize marketed inhaled drugs using data from the literature. The appropriateness of the classification of each drug was assessed based on published development, clinical and nonclinical data, and mechanistic physiologically based biopharmaceutics modeling. The inhaled drug product development challenges for each iBCS classification are discussed and illustrated for different classes of marketed inhaled drugs. Finally, it is recognized that discriminatory laboratory methods to characterize regional lung deposition, dissolution, and permeability will be key to fully realizing the benefits of an iBCS to streamline and derisk inhaled drug development.

For oral drugs, the formulator and discovery chemist have a tool available to them that can be used to navigate the risks associated with the selection and development of immediate release oral drugs and drug products. This tool is the biopharmaceutics classification system (giBCS). Unfortunately, no such classification system exists for inhaled drugs. The perspective outlined in this manuscript provides the foundational principles and framework for a classification system for inhaled drugs. The proposed classification system, an inhalation-based biopharmaceutics classification system (iBCS), is based on fundamental biopharmaceutics principles adapted to an inhalation route of administration framework. It is envisioned that a classification system for orally inhaled drugs will facilitate an understanding of the technical challenges associated with the development of new chemical entities and their associated new drug products (device and drug formulation combinations). Similar to the giBCS, the iBCS will be based on key attributes describing the drug substance (solubility and permeability) and the drug product (dose and dissolution). This manuscript provides the foundational aspects of an iBCS, including the proposed scientific principles and framework upon which such a system can be developed.

This work is the second in a series of publications outlining the fundamental principles and proposed design of a biopharmaceutics classifications system for inhaled drugs and drug products (the iBCS). Here, a mechanistic computer-based model has been used to explore the sensitivity of the primary biopharmaceutics functional output parameters: (i) pulmonary fraction dose absorbed (Fabs) and (ii) drug half-life in lumen (t1/2) to biopharmaceutics-relevant input attributes including dose number (Do) and effective permeability (Peff). Results show the nonlinear sensitivity of primary functional outputs to variations in these attributes. Drugs with Do < 1 and Peff > 1 × 10-6 cm/s show rapid (t1/2 < 20 min) and complete (Fabs > 85%) absorption from lung lumen into lung tissue. At Do > 1, dissolution becomes a critical drug product attribute and Fabs becomes dependent on regional lung deposition. The input attributes used here, Do and Peff, thus enabled the classification of inhaled drugs into parameter spaces with distinctly different biopharmaceutic risks. The implications of these findings with respect to the design of an inhalation-based biopharmaceutics classification system (iBCS) and to the need for experimental methodologies to classify drugs need to be further explored.

The purpose of this review is to summarize essential pharmacological, pharmaceutical, and clinical aspects in the field of orally inhaled therapies that may help scientists seeking to develop new products. After general comments on the rationale for inhaled therapies for respiratory disease, the focus is on products approved approximately over the last half a century. The organization of these sections reflects the key pharmacological categories. Products for asthma and chronic obstructive pulmonary disease include β -2 receptor agonists, muscarinic acetylcholine receptor antagonists, glucocorticosteroids, and cromones as well as their combinations. The antiviral and antibacterial inhaled products to treat respiratory tract infections are then presented. Two "mucoactive" products-dornase α and mannitol, which are both approved for patients with cystic fibrosis-are reviewed. These are followed by sections on inhaled prostacyclins for pulmonary arterial hypertension and the challenging field of aerosol surfactant inhalation delivery, especially for prematurely born infants on ventilation support. The approved products for systemic delivery via the lungs for diseases of the central nervous system and insulin for diabetes are also discussed. New technologies for drug delivery by inhalation are analyzed, with the emphasis on those that would likely yield significant improvements over the technologies in current use or would expand the range of drugs and diseases treatable by this route of administration. SIGNIFICANCE STATEMENT: This review of the key aspects of approved orally inhaled drug products for a variety of respiratory diseases and for systemic administration should be helpful in making judicious decisions about the development of new or improved inhaled drugs. These aspects include the choices of the active ingredients, formulations, delivery systems suitable for the target patient populations, and, to some extent, meaningful safety and efficacy endpoints in clinical trials.

The airways and lungs are the primary sites of SARS-CoV-2 entry, replication, and damage, so there is reason to administer drugs to these regions. Oral hydroxychloroquine (oHCQ) has produced mixed results in COVID-19, despite reported antiviral activity in vitro (EC50=0.72-119 μM). We tested the hypothesis that aerosolized HCQ sulfate (aHCQ) tolerably, safely, and rapidly achieves high respiratory tissue concentrations, while minimizing systemic toxicity. aHCQ was administered via Aerogen nebulizer (oral inhalation, nasal exhalation) to healthy volunteers in a Phase 1 study to assess tolerability, safety, and pharmacokinetics. 10 volunteers (age 55±13 years, 60% female) were randomized to Placebo (n=2), or aHCQ (20 mg, n=2; 50 mg, n=6); all completed the inhalation. 6/8 receiving aHCQ had adverse events (all mild; 75% transient dysgeusia, 25% dizziness). FEV1 and FVC were essentially unchanged from baseline after 15-360 minutes and 1 and 7 days. QT segments were minimally changed from baseline (maximum change 34 msec) after 1-6 hours, and 1 and 7 days; all were ≤455 msec. Pharmacokinetics of 50 mg: Area Under the Blood Curve 0-24 hours post-inhalation was 377±127 ng*hr/mL, <15% of that reported for oHCQ 200 mg; Pharmacokinetic modelling predicts initial epithelial lining fluid concentrations in excess of reported EC50s, and peak respiratory tissue concentrations of 0.5 mM, decreasing to 0.01 mM at 24 hours as HCQ slowly releases into blood. aHCQ was safe, well-tolerated, and appears to be sequestered in respiratory tissues. Administering aHCQ at a fraction of oral dosing may rapidly achieve respiratory tract concentrations sufficient to inhibit SARS-CoV-2.

Over the last decades, pharmacometric approaches became more widely applied to analyze the pharmacokinetics (PK) of drugs, ranging from empirical to mechanistic physiologically-based PK modeling. However, the number of published PBPK applications for orally inhaled drugs increased only recently, even though a mechanistic understanding would be essential when the local PK needs to be assessed to correctly infer on PK/PD relations. To illustrate how PBPK modeling can contribute to improve the understanding of the pulmonary fate of orally inhaled drugs, first the complex interplay of relevant pulmonary PK processes is explained and it is outlined how each of these can be incorporated into PBPK models. Besides theoretical considerations, examples are provided to review the current state of the art. Finally, this chapter provides an outlook on potential applications, opportunities but also limitations of PBPK modeling for orally inhaled drugs.

This book has comprehensively illustrated the current state of the art and discussed open issues in the three pillars of inhaled drug development, in vivo, in vitro and in silico methods that underpin the quality, safety and efficacy of a product. In this chapter, we argue that we have reached a point in the historical development of inhalation therapies, where these three methods will converge in support of integrated in silico tools. As a result, over the next few years we are likely to witness a significant enhancement of the capabilities of in silico methods and inferences for clinic application and drug product development.

Pulmonary dissolution of poorly soluble drug substances (DSs) may limit the drug absorption rate and consequently influence clinical performance. Dissolution rate is thus an important quality attribute, and its influence on in vivo drug release must be characterized, understood, and controlled early in the development process. The aim of this study is to establish an in vitro dissolution method with the capability to capture therapeutically relevant differences in the dissolution rate between drug batches and drug compounds. A method was developed by which a biorelevant aerosol fraction was captured on a filter using a sedimentation technique in a modified Andersen cascade impactor to avoid particle agglomeration. Subsequently, the filters were transferred to a commercial Transwell system where dissolution in 3 mL of phosphate buffer at pH 6.8 with 0.5% sodium dodecyl sulfate (SDS) occurred at sink conditions. Dissolved DS was quantified over time using UPLC-UV. Dissolution data was obtained on a series of micronized and aerosolized lipophilic DSs, budesonide, fluticasone furoate (FF), fluticasone propionate (FP), and AZD5423. The latter is a lipophilic AstraZeneca development compound available in two different mass median diameters (MMD), 1.3 (AZD54231.3) and 3.1 μm (AZD54233.1). Dissolution data were evaluated using a Weibull fit and expressed as t63, the time to dissolution of 63% of the initial dose. The following rank-order of t63 was obtained (mean t63 and MMD in brackets), budesonide (10 min, 2.1 μm) = AZD54231.3 (10 min, 1.3 μm) < AZD54233.1 (19 min, 3.1 μm) < FP (38 min, 2.4 μm) < FF (63 min, 2.5 μm). The method could differentiate between different drug compounds with different solubility but similar particle size distribution, as well as between the same drug compound with different particle size distributions. Furthermore, a relation between the in vitro dissolution rate ( t63) and mean pulmonary absorption time in man (literature data) was observed, indicating clinical relevance. It is thus concluded, that the method may be useful for the characterization and ranking of DSs and drug products in early development, as well as being a potential tool for the control of dissolution as a potential quality attribute.

Prediction of local exposure following inhalation of a locally acting pulmonary drug is central to the successful development of novel inhaled medicines, as well as generic equivalents. This work provides a comprehensive review of the state of the art with respect to multiscale computer models designed to provide a mechanistic prediction of local and systemic drug exposure following inhalation. The availability and quality of underpinning in vivo and in vitro data informing the computer based models is also considered. Mechanistic modelling of local exposure has the potential to speed up and improve the chances of successful inhaled API and product development. Although there are examples in the literature where this type of modelling has been used to understand and explain local and systemic exposure, there are two main barriers to more widespread use. There is a lack of generally recognised commercially available computational models that incorporate mechanistic modelling of regional lung particle deposition and drug disposition processes to simulate free tissue drug concentration. There is also a need for physiologically relevant, good quality experimental data to inform such modelling. For example, there are no standardized experimental methods to characterize the dissolution of solid drug in the lungs or measure airway permeability. Hence, the successful application of mechanistic computer models to understand local exposure after inhalation and support product development and regulatory applications hinges on: (i) establishing reliable, bio-relevant means to acquire experimental data, and (ii) developing proven mechanistic computer models that combine: a mechanistic model of aerosol deposition and post-deposition processes in physiologically-based pharmacokinetic models that predict free local tissue concentrations.

AZD5423 is a non-steroidal glucocorticoid receptor modulator, with low aqueous solubility, developed for treatment of asthma and COPD. In this work, we aim to evaluate and compare the absorption pharmacokinetics (PK) of AZD5423 after inhalation via four devices, (Spira®, I-neb®, Turbuhaler® and a new dry powder inhaler (new DPI)) with two formulations using differently sized primary particles, and to compare the pulmonary bioavailability with the predicted lung deposited dose. Plasma concentration-time data after intravenous, oral and inhaled administration via four devices were available from two clinical studies in healthy and asthmatic subjects. A population PK modelling approach was taken to sequentially incorporate each route of administration, assuming parallel absorption compartments for inhaled AZD5423. A non-compartmental analysis for derivation of PK parameters was performed for comparison. Pulmonary bioavailability varied between devices, with the lowest estimates for I-neb (27%) and Turbuhaler (30%) and the highest for the new DPI (46%) and Spira (35–49%). The pulmonary bioavailability was substantially lower than the predicted lung deposited dose (range 59–90%). Lung absorption was separated into a faster and a slower process in the model. The half-life of the faster absorption appeared formulation-dependent, while the slower absorption (half-life of 0.59–0.78 h) appeared independent of formulation. The large difference in the estimated pulmonary bioavailability and the predicted lung deposited dose for AZD5423 implies an impact of mucociliary clearance. The lung absorption half-life indicates that AZD5423 is retained in the lung for a relatively short time.

Permeation of inhaled drugs across the pulmonary epithelium can regulate the rate and extent of local drug absorption and hence the pulmonary tissue concentration. Therefore, understanding pulmonary epithelial transport could be important for successful design of novel inhaled medicines. To enhance understanding of pulmonary epithelial transport, drug transport data were generated for a set of inhaled compounds (n = 10) in the single-pass, isolated perfused rat lung model. A compartmental in silica model was used to estimate pulmonary permeability and tissue retention. The theoretical model was also used to re-analyze previously obtained historical drug transport data from the isolated perfused lung (n = 10) with re-circulating buffer. This was performed to evaluate the re-circulating model for assessing tissue retention measurements and to increase the number of data points. The tissue retention was an important parameter to estimate to be able to describe the drug transport profiles accurately of most of the investigated compounds. A relationship between the pulmonary permeability and the intrinsic (carrier-mediated transport inhibited) permeability of Caco-2 cell monolayers (n = 1-6) was also established. This correlation (R-2 = 0.76, p < .0001) suggests that intrinsic Caco-2 permeability measurements could offer early predictions of the passive transcellular permeability of lung epithelium to candidate drugs. Although, for some compounds a deviation from the correlation suggests that other transport mechanisms may coexist. The compartmental in silica model was successful in describing the pulmonary drug transport profiles of the investigated compounds and has potential for further development to investigate the effects of formulations with different features on the pulmonary overall absorption rate.

BACKGROUND:Exposure following oral inhalation depends on the deposition pattern of the inhaled aerosol, the extent and rate of oral and pulmonary absorption, as well as systemic distribution and clearance. For lipophilic inhaled compounds with low water solubility and high permeability, the extent and rate of pulmonary absorption can be assumed dependent on deposition pattern as well as dissolution rate.MATERIALS AND METHODS:A mechanistic model of airway deposition, mucociliary clearance, dissolution, absorption, and dissipation was applied to simulate systemic exposure of the novel selective glucocorticoid receptor modulator, AZD5423, when dosed to healthy volunteers using two different nebulizers and two different dry powder inhalers in combination with two different primary particle size distributions. Results from simulations were compared with observed pharmacokinetic data.RESULTS:Variations in systemic exposure (plasma concentration profile, AUC, and Cmax) resulting from variations in dose, deposition pattern, and dissolution rate could not be predicted solely from variations in delivered dose or predicted lung dose (as assessed using an anatomical mouth-throat model), suggesting incomplete pulmonary bioavailability. However, simulated systemic exposure well predicted observed systemic exposures for all tested formulations and devices. Furthermore, simulations of airway tissue exposure suggested that it was not directly linked to systemic exposure.CONCLUSIONS:Results support the initial hypothesis that systemic exposure of poorly soluble inhaled drugs is a complex but predictable function of dose, deposition pattern, and rate of dissolution. Furthermore, simulations indicate that local exposure for these types of drugs is not well correlated with systemic exposure. Hence, equivalence with respect to local exposure, and thus with respect to pharmacodynamic effect, cannot be fully inferred from systemic pharmacokinetic equivalence alone.

The lung surfactant (LS) lining is a thin liquid film covering the air-liquid interface of the respiratory tract. LS reduces surface tension, enabling lung surface expansion and contraction with minimal work during respiration. Disruption of surface tension is believed to play a key role in severe lung conditions. Inhalation of aerosols that interfere with the LS may induce a toxic response and, as a part of the safety assessment of chemicals and inhaled medicines, it may be relevant to study their impact on LS function. Here, we present a novel in vitro method, based on the constrained drop surfactometer, to study LS functionality after aerosol exposure. The applicability of the method was investigated using three inhaled asthma medicines, micronized lactose, a pharmaceutical excipient used in inhaled medication, and micronized albumin, a known inhibitor of surfactant function. The surfactometer was modified to allow particles mixed in air to flow through the chamber holding the surfactant drop. The deposited dose was measured with a custom-built quartz crystal microbalance. The alterations allowed the study of continuously increasing quantified doses of particles, allowing determination of the dose of particles that affects the LS function. The tested pharmaceuticals did not inhibit the function of a model LS even at extreme doses-neither did lactose. Micronized albumin, however, impaired surfactant function. The method can discriminate between safe inhaled aerosols-as exemplified by the approved inhaled medicines and the pharmaceutical excipient lactose-and albumin known to impair lung functionality by inhibiting LS function.