Scope and relevance of a pulmonary biopharmaceutical classification system AAPS/FDA/USP Workshop March 16-17th, 2015 in Baltimore, MD

Microstructural Characterization of Dry Powder Inhaler Formulations Using Orthogonal Analytical Techniques

PURPOSE

For locally-acting dry powder inhalers (DPIs), developing novel analytical tools that are able to evaluate the state of aggregation may provide a better understanding of the impact of material properties and processing parameters on the in vivo performance. This study explored the utility of the Morphologically-Directed Raman Spectroscopy (MDRS) and dissolution as orthogonal techniques to assess microstructural equivalence of the aerosolized dose of DPIs collected with an aerosol collection device.

METHODS

Commercial DPIs containing different strengths of Fluticasone Propionate (FP) and Salmeterol Xinafoate (SX) as monotherapy and combination products were sourced from different regions. These inhalers were compared with aerodynamic particle size distribution (APSD), dissolution, and MDRS studies.

RESULTS

APSD testing alone might not be able to explain differences reported elsewhere in in vivo studies of commercial FP/SX drug products with different Advair® strengths and/or batches. Dissolution studies demonstrated different dissolution rates between Seretide™ 100/50 and Advair® 100/50, whereas Flixotide™ 100 and Flovent® 100 had similar dissolution rates between each other. These differences in dissolution profiles were supported by MDRS results: the dissolution rate is increased if the fraction of FP associated with high soluble components is increased. Principle component analysis was used to identify the agglomerate classes that better discriminate different products.

CONCLUSIONS

MDRS and dissolution studies of the aerosolized dose of DPIs were successfully used as orthogonal techniques. This study highlights the importance of further assessing in vitro tools that are able to provide a bridge between material attributes or process parameters and in vivo performance.

An Exploration of Dissolution Tests for Inhalation Aerosols

This study aimed to establish a feasible dissolution method for inhalation aerosols. A method of collecting fine particles was investigated to capture aerosol particles less than 4 μm in diameter for dissolution tests. This dose collection method enabled the aerosol particles to be uniformly distributed on the glass fiber filter, thus considerably reducing particle agglomeration. Budesonide was used as a model drug. The aerodynamic particle size distribution (APSD) of the meter-dose inhaler (MDI) was compared by replacing actuators with different orifice sizes. Dissolution tests were conducted on fine particle doses collected using various actuators, and the dissolution profiles were modeled. The fine particle dose decreased with an increasing orifice size of the actuator. Actuators with different orifice sizes would affect the dissolution behavior of inhaled drugs. This finding was supported by similarity factor f2 analysis, suggesting the dissolution method has a discriminative capacity. The results of various model fits showed that the dissolution profiles produced by the different actuators could be fitted well using the Weibull mathematical model. The method employed in this study could offer a potential avenue for exploring the relationship between the orifice size of the actuator and the dissolution behavior of inhaled corticosteroids. This dissolution method was simple, reproducible, and suitable for determining the dissolution of inhalation aerosols.

Integration of mucus and its impact within in vitro setups for inhaled drugs and formulations: Identifying the limits of simple vs. complex methodologies when studying drug dissolution and permeability

Traditionally, developing inhaled drug formulations relied on trial and error, yet recent technological advancements have deepened the understanding of 'inhalation biopharmaceutics' i.e. the processes that occur to influence the rate and extent of drug exposure in the lungs. This knowledge has led to the development of new in vitro models that predict the in vivo behavior of drugs, facilitating the enhancement of existing formulation and the development of novel ones. Our prior research examined how simulated lung fluid (SLF) affects the solubility of inhaled drugs. Building on this, we aimed to explore drug dissolution and permeability in lung mucosa models containing mucus. Thus, the permeation of four active pharmaceutical ingredients (APIs), salbutamol sulphate (SS), tiotropium bromide (TioBr), formoterol fumarate (FF) and budesonide (BUD), was assayed in porcine mucus covered Calu-3 cell layers, cultivated at an air liquid interface (ALI) or submerged in a liquid covered (LC) culture system. Further analysis on BUD and FF involved their transport in a mucus-covered PAMPA system. Finally, their dissolution post-aerosolization from Symbicort® was compared using 'simple' Transwell and complex DissolvIt® apparatuses, alone or in presence of porcine mucus or polymer-lipid mucus simulant. The presence of porcine mucus impacted both permeability and dissolution of inhaled drugs. For instance, permeability of SS was reduced by a factor of ten in the Calu-3 ALI model while the permeability of BUD was reduced by factor of two in LC and ALI setups. The comparison of dissolution methodologies indicated that drug dissolution performance was highly dependent on the setup, observing decreased release efficiency and higher variability in Transwell system compared to DissolvIt®. Overall, results demonstrate that relatively simple methodologies can be used to discriminate between formulations in early phase drug product development. However, for more advanced stages complex methods are required. Crucially, it was clear that the impact of mucus and selection of its composition in in vitro testing of dissolution and permeability should not be neglected when developing drugs and formulations intended for inhalation.

Optimization of an in vitro method for assessing pulmonary permeability of inhaled drugs using alveolar epithelial cells

INTRODUCTION

Inhalation of drugs for the treatment of pulmonary diseases has been used since a long time. Due to lungs' larger absorptive surface area, delivery of drugs to the lungs is the method of choice for different disorders. Here we present the establishment of a comprehensive permeability model using Type II alveolar epithelial cells and Beclomethasone Dipropionate (BDP) as a model drug delivered by pressurized metered dose inhaler (pMDI).

METHODS

Using Type II alveolar epithelial cells, the method was standardized for parameters viz., cell density, viability, incubation period and membrane integrity. The delivery and deposition of drug were using the pMDI device with a Twin Stage Impinger (TSI) modified to accommodate cell culture insert having monolayer of cells. The analytical method for simultaneous estimation of BDP and Beclomathasone-17-Monopropionate (17-BMP) was validated as per the bioanalytical guidelines. The extent and rate of absorption of BDP was determined by quantifying the amount of drug permeated and the data represented by calculating its apparent permeability.

RESULTS

Type II alveolar epithelial cells cultured at 0.55 × 105 cells/cm2 for 8-12 days under air-liquid interface were optimized for conducting permeability studies. The data obtained for absorptive transport showed a linear increase in the drug permeated against time for both BDP and 17-BMP along with proportional permeability profile.

DISCUSSION

We have developed a robust in vitro model to study absorptive rate of drug transport across alveolar layer. Such models would create potential value during formulation development for comparative studies and selection of clinical candidates.

Drug solubility in biorelevant media in the context of an inhalation-based biopharmaceutics classification system (iBCS)

An inhalation-based Biopharmaceutics Classification System for pulmonary drugs (iBCS) holds the perspective to allow for scientifically sound prediction of differences in the in vivo performance of orally inhaled drug products (OIDPs). A set of nine drug substances were selected, that are administered via both the oral and pulmonary routes. Their solubility was determined in media representative for the oral (Fasted State Simulated Intestinal Fluid (FaSSIF)) and pulmonary (Alveofact medium and Simulated Lung Fluid (SLF)) routes of administration to confirm the need for a novel approach for inhaled drugs. The complexity of these media was then stepwise reduced with the purpose of understanding the contribution of their components to the solubilizing capacity of the media. A second reason for varying the complexity was to identify a medium that would allow robust but accurate dissolution testing. Hence, Hank's balanced salt solution (HBSS) as a medium used in many in vitro biological tests, non-buffered saline solution, and water were included. For some drug substances (salbutamol sulfate, tobramycin, isoniazid, and tiotropium bromide), no significant differences were observed between the solubility in the media used. For other drugs, however, we observed either just small (rifampicin, budesonide, salmeterol) or unexpectedly large differences (beclomethasone dipropionate). Based on the minimum theoretical solubility required for their common pulmonary dose in 10 ml of lung lining fluid, drug solubility was classified as either high or low. Two high solubility and two low solubility compounds were then selected for refined solubility testing in pulmonary relevant media by varying their content of phospholipids, surfactant proteins and other proteins. The solubility of drug substances in simulated lung lining fluids was found to be dependent on the physicochemical properties of the drug substance and the composition of the media. While a pulmonary dissolution medium that would fit all drugs could not be established, our approach may provide guidance for finding the most suitable dissolution medium for a given drug substance and better designing in vitro tests for predicting the in vivo performance of inhalable drug products.

iBCS: 3. A Biopharmaceutics Classification System for Orally Inhaled Drug Products

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.

Nano vs Resistant Tuberculosis: Taking the Lung Route

Tuberculosis (TB) is among the top 10 infectious diseases worldwide. It is categorized among the leading killer diseases that are the reason for the death of millions of people globally. Although a standardized treatment regimen is available, non-adherence to treatment has increased multi-drug resistance (MDR) and extensive drug-resistant (XDR) TB development. Another challenge is targeting the death of TB reservoirs in the alveoli via conventional treatment. TB Drug resistance may emerge as a futuristic restraint of TB with the scarcity of effective Anti-tubercular drugs. The paradigm change towards nano-targeted drug delivery systems is mostly due to the absence of effective therapy and increased TB infection recurrent episodes with MDR. The emerging field of nanotechnology gave an admirable opportunity to combat MDR and XDR via accurate diagnosis with effective treatment. The new strategies targeting the lung via the pulmonary route may overcome the new incidence of MDR and enhance patient compliance. Therefore, this review highlights the importance and recent research on pulmonary drug delivery with nanotechnology along with prevalence, the need for the development of nanotechnology, beneficial aspects of nanomedicine, safety concerns of nanocarriers, and clinical studies.

Liposomal drug delivery to the lungs: a post covid-19 scenario

High local delivery of anti-infectives to the lungs is required for activity against infections of the lungs. The present pandemic has highlighted the potential of pulmonary delivery of anti-infective agents as a viable option for infections like Covid-19, which specifically causes lung infections and mortality. To prevent infections of such type and scale in the future, target-specific delivery of drugs to the pulmonary region is a high-priority area in the field of drug delivery. The suboptimal effect of oral delivery of anti-infective drugs to the lungs due to the poor biopharmaceutical property of the drugs makes this delivery route very promising for respiratory infections. Liposomes have been used as an effective delivery system for drugs due to their biocompatible and biodegradable nature, which can be used effectively for target-specific drug delivery to the lungs. In the present review, we focus on the use of liposomal drug delivery of anti-infectives for the acute management of respiratory infections in the wake of Covid-19 infection.

Computational fluid dynamics modeling of aerosol particle transport through lung airway mucosa

Delivery of aerosols to the lung can treat various lung diseases. However, the conducting airways are coated by a protective mucus layer with complex properties that make this form of delivery difficult. Mucus is a non-Newtonian fluid and is cleared from the lungs over time by ciliated cells. Further, its gel-like structure hinders the diffusion of particles through it. Any aerosolized treatment of lung diseases must penetrate the mucosal barrier. Using computational fluid dynamics, a model of the airway mucus and periciliary layer was constructed to simulate the transport of impacted aerosol particles. The model predicts the dosage fraction of particles of a certain size that penetrate the mucus and reach the underlying tissue, as well as the distance downstream of the dosage site where tissue concentration is maximized. Reactions that may occur in the mucus are also considered, with simulated data for the interaction of a model virus and an antibody.

Nebulizers effectiveness on pulmonary delivery of alpha-1 antitrypsin

The nebulization of alpha-1 antitrypsin (AAT) for its administration to the lung could be an interesting alternative to parenteral infusion for patients suffering from AAT genetic deficiency (AATD). In the case of protein therapeutics, the effect of the nebulization mode and rate on protein conformation and activity must be carefully considered. In this paper two types of nebulizers, i.e., a jet and a mesh vibrating system, were used to nebulize a commercial preparation of AAT for infusion and compared. The aerosolization performance, in terms of mass distribution, respirable fraction, and drug delivery efficiency, as well as the activity and aggregation state of AAT upon in vitro nebulization were investigated. The two nebulizers demonstrated equivalent aerosolization performances, but the mesh nebulizer provided a higher efficiency in the delivery of the dose. The activity of the protein was acceptably preserved by both nebulizers and no aggregation or changes in its conformation were identified. This suggests that nebulization of AAT represents a suitable administration strategy ready to be translated to the clinical practice for delivering the protein directly to the lungs in AATD patients, either as a support therapy to parenteral administration or for subjects with a precocious diagnosis, to prevent the onset of pulmonary symptoms.

In Vitro and In Vivo Evaluation of Inhalable Ciprofloxacin Sustained Release Formulations

Respiratory antibiotics delivery has been appreciated for its high local concentration at the infection sites. Certain formulation strategies are required to improve pulmonary drug exposure and to achieve effective antimicrobial activity, especially for highly permeable antibiotics. This study aimed to investigate lung exposure to various inhalable ciprofloxacin (CIP) formulations with different drug release rates in a rat model. Four formulations were prepared, i.e., CIP-loaded PLGA micro-particles (CHPM), CIP microcrystalline dry powder (CMDP), CIP nanocrystalline dry powder (CNDP), and CIP spray-dried powder (CHDP), which served as a reference. The physicochemical properties, drug dissolution rate, and aerosolization performance of these powders were characterized in vitro. Pharmacokinetic profiles were evaluated in rats. All formulations were suitable for inhalation (mass median aerodynamic diameter < 5 µm). CIP in CHPM and CHDP was amorphous, whereas the drug in CMDP and CNDP remained predominantly crystalline. CHDP exhibited the fastest drug release rate, while CMDP and CNDP exhibited much slower drug release. In addition, CMDP and CNDP exhibited significantly higher in vivo lung exposure to CIP compared with CHDP and CHPM. This study suggests that lung exposure to inhaled drugs with high permeability is governed by drug release rate, implying that lung exposure of inhaled antibiotics could be improved by a sustained-release formulation strategy.

Spray Dried Progesterone Formulations for Carrier Free Dry Powder Inhalation

Low oral absorption and extensive first pass metabolism of progesterone is reported for many oral formulations which warrants investigation into other routes of administration. It is the aim of this study to investigate the generation of inhaled formulations of progesterone though a spray drying approach with a focus on how spray drying impacts the physicochemical properties of progesterone. Formulations of progesterone with L-leucine and hydroxypropyl methylcellulose acetate succinate (HPMCAS) are reported to this aim. X-ray diffraction, spectroscopy and thermal analysis were used to characterise these formulations and confirmed that progesterone crystallises as the Form II polymorph during spray drying regardless of the solvent used. The resultant formulations showed higher aqueous solubility than progesterone Form I starting material and the addition of HPMCAS was shown to temporarily enable a supersaturated state. Thermal analysis was used to show that the Form II polymorph was sensitive to transformation to Form I during heating. The addition of L-leucine to the formulations reduced the temperature for the polymorphic transformation by ∼10 °C. However, when HPMCAS was added to the formulation, the Form II polymorph was prevented from transforming to the Form I polymorph. Cascade impaction was used to determine the aerosol performance of the spray dried powders and showed promising lung deposition profiles (mass median aerodynamic diameter 5 µm) with significant variation depending on the organic solvent used and the ratio of organic to aqueous phase in the feedstock. However, further optimisation of formulations was required to direct more progesterone into the alveolar regions. The addition of HPMCAS was seen to increase the alveolar deposition and therefore formed a formulation with a lower fine particle fraction and mass median aerodynamic diameter. The most suitable formulation for inhalation was formed from a 50:50 acetone:water destockck and showed an ED, FPF and FPD of 81.7%, 44.5% and 7.3 mg respectively. Therefore, HPMCAS is suggested as a suitable excipient to increase solubility, prevent polymorphic transformation and improve inhalation properties of spray dried progesterone formulations. This study highlights the use of spray drying to form inhalable progesterone powders with higher solubility which may broaden the application of this medicine.

Aerosol technology to mimic dry powder inhalation in vitro using pulmonary cell models

Inhaled therapy confers key advantages for the treatment of topical pulmonary diseases and offers potential for systemic delivery of medicines. Dry powder inhalers (DPIs) are generally the preferred devices for pulmonary delivery due to improved stability and satisfactory patient compliance. However, the mechanisms governing drug powder dissolution and availability in the lung and poorly understood. Here, we report a new in vitro system to study epithelial absorption of inhaled dry powders in lung barrier models of the upper and lower airway. The system is based on a CULTEX® RFS (Radial Flow System) cell exposure module joined to a Vilnius aerosol generator and allows the coupling of drug dissolution and permeability assessments. The cellular models recapitulate the barrier morphology and function of healthy and diseased pulmonary epithelium and incorporate the mucosal barrier to enable the investigation of drug powder dissolution in biorelevant conditions. With this system, we found differences in permeability across the airway tree and pinpointed the impact of diseased barriers in paracellular drug transport. Furthermore, we identified a different rank order of permeability for compounds tested in solution or powder form. These results highlight the value of this in vitro drug aerosolization setup for use in research and development of inhaled medicines.

In Vitro Dissolution and Permeability Testing of Inhalation Products: Challenges and Advances

In vitro dissolution and permeability testing aid the simulation of the in vivo behavior of inhalation drug products. Although the regulatory bodies have specific guidelines for the dissolution of orally administered dosage forms (e.g., tablets and capsules), this is not the case for orally inhaled formulations, as there is no commonly accepted test for assessing their dissolution pattern. Up until a few years ago, there was no consensus that assessing the dissolution of orally inhaled drugs is a key factor in the assessment of orally inhaled products. With the advancement of research in the field of dissolution methods for orally inhaled products and a focus on systemic delivery of new, poorly water-soluble drugs at higher therapeutic doses, an evaluation of dissolution kinetics is proving crucial. Dissolution and permeability testing can determine the differences between the developed formulations and the innovator’s formulations and serve as a useful tool in correlating in vitro and in vivo studies. The current review highlights recent advances in the dissolution and permeability testing of inhalation products and their limitations, including recent cell-based technology. Although a few new dissolution and permeability testing methods have been established that have varying degrees of complexity, none have emerged as the standard method of choice. The review discusses the challenges of establishing methods that can closely simulate the in vivo absorption of drugs. It provides practical insights into method development for various dissolution testing scenarios and challenges with dose collection and particle deposition from inhalation devices for dissolution tests. Furthermore, dissolution kinetic models and statistical tests to compare the dissolution profiles of test and reference products are discussed.

An evolving perspective on novel modified release drug delivery systems for inhalational therapy

INTRODUCTION

Drugs delivered via the lungs are predominantly used to treat various respiratory disorders, including asthma, chronic obstructive pulmonary diseases, respiratory tract infections and lung cancers, and pulmonary vascular diseases such as pulmonary hypertension. To treat respiratory diseases, targeted, modified or controlled release inhalation formulations are desirable for improved patient compliance and superior therapeutic outcome.

AREAS COVERED

This review summarizes the important factors that have an impact on the inhalable modified release formulation approaches with a focus toward various formulation strategies, including dissolution rate-controlled systems, drug complexes, site-specific delivery, drug-polymer conjugates, and drug-polymer matrix systems, lipid matrix particles, nanosystems, and formulations that can bypass clearance via mucociliary system and alveolar macrophages.

EXPERT OPINION

Inhaled modified release formulations can potentially reduce dosing frequency by extending drug's residence time in the lungs. However, inhalable modified or controlled release drug delivery systems remain unexplored and underdeveloped from the commercialization perspective. This review paper addresses the current state-of-the-art of inhaled controlled release formulations, elaborates on the avenues for developing newer technologies for formulating various drugs with tailored release profiles after inhalational delivery and explains the challenges associated with translational feasibility of modified release inhalable formulations.

Assessing the in vitro toxicity of airborne (nano)particles to the human respiratory system: from basic to advanced models

Several studies have been conducted to address the potential adverse health risks attributed to exposure to nanoscale materials. While in vivo studies are fundamental for identifying the relationship between dose and occurrence of adverse effects, in vitro model systems provide important information regarding the mechanism(s) of action at the molecular level. With a special focus on exposure to inhaled (nano)particulate material toxicity assessment, this review provides an overview of the available human respiratory models and exposure systems for in vitro testing, advantages, limitations, and existing investigations using models of different complexity. A brief overview of the human respiratory system, pathway and fate of inhaled (nano)particles is also presented.

Engineering the right formulation for enhanced drug delivery

Dry powder inhalers (DPIs) can be used with a wide range of drugs such as small molecules and biologics and offer several advantages for inhaled therapy. Early DPI products were intended to treat asthma and lung chronic inflammatory disease by administering low-dose, high-potency drugs blended with lactose carrier particles. The use of lactose blends is still the most common approach to aid powder flowability and dose metering in DPI products. However, this conventional approach may not meet the high demand for formulation physical stability, aerosolisation performance, and bioavailability. To overcome these issues, innovative techniques coupled with modification of the traditional methods have been explored to engineer particles for enhanced drug delivery. Different particle engineering techniques have been utilised depending on the types of the active pharmaceutical ingredient (e.g., small molecules, peptides, proteins, cells) and the inhaled dose. This review discusses the challenges of formulating DPI formulations of low-dose and high-dose small molecule drugs, and biologics, followed by recent and emerging particle engineering strategies utilised in developing the right inhalable powder formulations for enhanced drug delivery.

Dissolution and Absorption of Inhaled Drug Particles in the Lungs

Dry powder inhalation therapy has been effective in treating localized lung diseases such asthma, chronic obstructive pulmonary diseases (COPD), cystic fibrosis and lung infections. In vitro characterization of dry powder formulations includes the determination of physicochemical nature and aerosol performance of powder particles. The relationship between particle properties (size, shape, surface morphology, porosity, solid state nature, and surface hydrophobicity) and aerosol performance of an inhalable dry powder formulation has been well established. However, unlike oral formulations, there is no standard dissolution method for evaluating the dissolution behavior of the inhalable dry powder particles in the lungs. This review focuses on various dissolution systems and absorption models, which have been developed to evaluate dry powder formulations. It covers a summary of airway epithelium, hurdles to developing an in vitro dissolution method for the inhaled dry powder particles, fine particle dose collection methods, various in vitro dissolution testing methods developed for dry powder particles, and models commonly used to study absorption of inhaled drug.

iBCS. 2: Mechanistic Modeling of Pulmonary Availability of Inhaled Drugs versus Critical Product Attributes

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 (F_abs) and (ii) drug half-life in lumen (t_1/2) to biopharmaceutics-relevant input attributes including dose number (Do) and effective permeability (P_eff). Results show the nonlinear sensitivity of primary functional outputs to variations in these attributes. Drugs with Do < 1 and P_eff > 1 × 10^-6 cm/s show rapid (t_1/2 < 20 min) and complete (F_abs > 85%) absorption from lung lumen into lung tissue. At Do > 1, dissolution becomes a critical drug product attribute and F_abs becomes dependent on regional lung deposition. The input attributes used here, Do and P_eff, 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.

High dose nanocrystalline solid dispersion powder of voriconazole for inhalation

In the current work, we aimed to deliver high dose of voriconazole (VRC) to lung through dry powder for inhalation (DPIs). Furthermore, the research tested the hypothesis that drug nanocrystals can escape the clearance mechanisms in lung by virtue of their size and rapid dissolution. High dose nanocrystalline solid dispersion (NCSD) based DPI of VRC was prepared using a novel spray drying process. Mannitol (MAN) and soya lecithin (LEC) were used as crystallization inducer and stabilizer, respectively. The powders were characterized for physicochemical and aerodynamic properties. Chemical interactions contributing to generation and stabilization of VRC nanocrystals in the matrix of MAN were established using computational studies. Performance of NCSD (VRC-N) was compared with microcrystalline solid dispersion (VRC-M) in terms of dissolution, uptake in A549 and RAW 264.7 cells. Plasma and lung distribution of VRC-N and VRC-M in Balb/c mice upon insufflation was compared with the intravenous product. In VRC-N, drug nanocrystals of size 645.86 ± 56.90 nm were successfully produced at VRC loading of 45%. MAN created physical barrier to crystal growth by interacting with N- of triazole and F- of pyrimidine ring of VRC. An increase in drug loading to 60% produced VRC crystals of size 4800 ± 200 nm (VRC-M). The optimized powders were crystalline and showed deposition at stage 2 and 3 in NGI. In comparison to VRC-M, more than 80% of VRC-N dissolved rapidly in around 5-10 mins, therefore, showed higher and lower drug uptake into A549 and RAW 264.7 cells, respectively. In contrast to intravenous product, insufflation of VRC-N and VRC-M led to higher drug concentrations in lung in comparison to plasma. VRC-N showed higher lung AUC_0-24 due to escape of macrophage clearance.

iBCS: 1. Principles and Framework of an Inhalation-Based Biopharmaceutics Classification System

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.

Inhaled antibodies: Quality and performance considerations

The use of antibodies in the treatment of lung diseases is of increasing interest especially as the search for COVID-19 therapies has unfolded. Historically, the use of antibody therapy was based on multiple targets including receptors involved in local hyper-reactivity in asthma, viruses and micro-organisms involved in a variety of pulmonary infectious disease. Generally, protein therapeutics pose challenges with respect to formulation and delivery to retain activity and assure therapy. The specificity of antibodies amplifies the need for attention to molecular integrity not only in formulation but also during aerosol delivery for pulmonary administration. Drug product development can be viewed from considerations of route of administration, dosage form, quality, and performance measures. Nebulizers and dry powder inhalers have been used to deliver protein therapeutics and each has its advantages that should be matched to the needs of the drug and the disease. This review offers insight into quality and performance barriers and the opportunities that arise from meeting them effectively.

Inhaled Antifungal Agents for Treatment and Prophylaxis of Bronchopulmonary Invasive Mold Infections

Pulmonary mold infections are life-threatening diseases with high morbi-mortalities. Treatment is based on systemic antifungal agents belonging to the families of polyenes (amphotericin B) and triazoles. Despite this treatment, mortality remains high and the doses of systemic antifungals cannot be increased as they often lead to toxicity. The pulmonary aerosolization of antifungal agents can theoretically increase their concentration at the infectious site, which could improve their efficacy while limiting their systemic exposure and toxicity. However, clinical experience is poor and thus inhaled agent utilization remains unclear in term of indications, drugs, and devices. This comprehensive literature review aims to describe the pharmacokinetic behavior and the efficacy of inhaled antifungal drugs as prophylaxes and curative treatments both in animal models and humans.

In vitro and ex vivo models in inhalation biopharmaceutical research - advances, challenges and future perspectives

Oral inhalation results in pulmonary drug targeting and thereby reduces systemic side effects, making it the preferred means of drug delivery for the treatment of respiratory disorders such as asthma, chronic obstructive pulmonary disease or cystic fibrosis. In addition, the high alveolar surface area, relatively low enzymatic activity and rich blood supply of the distal airspaces offer a promising pathway to the systemic circulation. This is particularly advantageous when a rapid onset of pharmacological action is desired or when the drug is suffering from stability issues or poor biopharmaceutical performance following oral administration. Several cell and tissue-based in vitro and ex vivo models have been developed over the years, with the intention to realistically mimic pulmonary biological barriers. It is the aim of this review to critically discuss the available models regarding their advantages and limitations and to elaborate further which biopharmaceutical questions can and cannot be answered using the existing models.

Optimizing Spray-Dried Porous Particles for High Dose Delivery with a Portable Dry Powder Inhaler

This manuscript critically reviews the design and delivery of spray-dried particles for the achievement of high total lung doses (TLD) with a portable dry powder inhaler. We introduce a new metric termed the product density, which is simply the TLD of a drug divided by the volume of the receptacle it is contained within. The product density is given by the product of three terms: the packing density (the mass of powder divided by the volume of the receptacle), the drug loading (the mass of drug divided by the mass of powder), and the aerosol performance (the TLD divided by the mass of drug). This manuscript discusses strategies for maximizing each of these terms. Spray drying at low drying rates with small amounts of a shell-forming excipient (low Peclet number) leads to the formation of higher density particles with high packing densities. This enables ultrahigh TLD (>100 mg of drug) to be achieved from a single receptacle. The emptying of powder from capsules is directly proportional to the mass of powder in the receptacle, requiring an inhaled volume of about 1 L for fill masses between 40 and 50 mg and up to 3.2 L for a fill mass of 150 mg.

Mannitol Polymorphs as Carrier in DPIs Formulations: Isolation Characterization and Performance

The search for best performing carriers for dry powder inhalers is getting a great deal of interest to overcome the limitations posed by lactose. The aerosolization of adhesive mixtures between a carrier and a micronized drug is strongly influenced by the carrier solid-state properties. This work aimed at crystallizing kinetically stable D-mannitol polymorphs and at investigating their aerosolization performance when used in adhesive mixtures with two model drugs (salbutamol sulphate, SS, and budesonide, BUD) using a median and median/high resistance inhaler. A further goal was to assess in vitro the cytocompatibility of the produced polymer-doped mannitol polymorphs toward two lung epithelial cell lines. Kinetically stable (up to 12 months under accelerate conditions) α, and δ mannitol forms were crystallized in the presence of 2% w/w PVA and 1% w/w PVP respectively. These solid phases were compared with the β form and lactose as references. The solid-state properties of crystallized mannitol significantly affected aerosolization behavior, with the δ form affording the worst fine particle fraction with both the hydrophilic (9.3 and 6.5%) and the lipophilic (19.6 and 32%) model drugs, while α and β forms behaved in the same manner (11–13% for SS; 53–58% for BUD) and better than lactose (8 and 13% for SS; 26 and 39% for BUD). Recrystallized mannitol, but also PVA and PVP, proved to be safe excipients toward lung cell lines. We concluded that, also for mannitol, the physicochemical properties stemming from different crystal structures represent a tool for modulating carrier-drug interaction and, in turn, aerosolization performance.

Optimization of the Transwell® System for Assessing the Dissolution Behavior of Orally Inhaled Drug Products through In Vitro and In Silico Approaches

The aim of this study was to further evaluate and optimize the Transwell^® system for assessing the dissolution behavior of orally inhaled drug products (OIDPs), using fluticasone propionate as a model drug. Sample preparation involved the collection of a relevant inhalable dose fraction through an anatomical mouth/throat model, resulting in a more uniform presentation of drug particles during the subsequent dissolution test. The method differed from previously published procedures by (1) using a 0.4 µm polycarbonate (PC) membrane, (2) stirring the receptor compartment, and (3) placing the drug-containing side of the filter paper face downwards, towards the PC membrane. A model developed in silico, paired with the results of in vitro studies, suggested that a dissolution medium providing a solubility of about 5 µg/mL would be a good starting point for the method's development, resulting in mean transfer times that were about 10 times longer than those of a solution. Furthermore, the model suggested that larger donor/receptor and sampling volumes (3, 3.3 and 2 mL, respectively) will significantly reduce the so-called "mass effect". The outcomes of this study shed further light on the impact of experimental conditions on the complex interplay of dissolution and diffusion within a volume-limited system, under non-sink conditions.

Innovating on Inhaled Bioequivalence: A Critical Analysis of the Current Limitations, Potential Solutions and Stakeholders of the Process

Orally inhaled drug products (OIDPs) are an important group of medicines traditionally used to treat pulmonary diseases. Over the past decade, this trend has broadened, increasing their use in other conditions such as diabetes, expanding the interest in this administration route. Thus, the bioequivalence of OIDPs is more important than ever, aiming to increase access to affordable, safe and effective medicines, which translates into better public health policies. However, regulatory agencies leading the bioequivalence process are still deciding the best approach for ensuring a proposed inhalable product is bioequivalent. This lack of agreement translates into less cost-effective strategies to determine bioequivalence, discouraging innovation in this field. The Next-Generation Impactor (NGI) is an example of the slow pace at which the inhalation field evolves. The NGI was officially implemented in 2003, being the last equipment innovation for OIDP characterization. Even though it was a breakthrough in the field, it did not solve other deficiencies of the BE process such as dissolution rate analysis on physiologically relevant conditions, being the last attempt of transferring technology into the field. This review aims to reveal the steps required for innovation in the regulations defining the bioequivalence of OIDPs, elucidating the pitfalls of implementing new technologies in the current standards. To do so, we collected the opinion of experts from the literature to explain these trends, showing, for the first time, the stakeholders of the OIDP market. This review analyzes the stakeholders involved in the development, improvement and implementation of methodologies that can help assess bioequivalence between OIDPs. Additionally, it presents a list of methods potentially useful to overcome some of the current limitations of the bioequivalence standard methodologies. Finally, we review one of the most revolutionary approaches, the inhaled Biopharmaceutical Classification System (IBCs), which can help establish priorities and order in both the innovation process and in regulations for OIDPs.

A Pathway From Porous Particle Technology Toward Tailoring Aerogels for Pulmonary Drug Administration

Pulmonary drug delivery has recognized benefits for both local and systemic treatments. Dry powder inhalers (DPIs) are convenient, portable and environmentally friendly devices, becoming an optimal choice for patients. The tailoring of novel formulations for DPIs, namely in the form of porous particles, is stimulating in the pharmaceutical research area to improve delivery efficiency. Suitable powder technological approaches are being sought to design such formulations. Namely, aerogel powders are nanostructured porous particles with particularly attractive properties (large surface area, excellent aerodynamic properties and high fluid uptake capacity) for these purposes. In this review, the most recent development on powder technologies used for the processing of particulate porous carriers are described via updated examples and critically discussed. A special focus will be devoted to the most recent advances and uses of aerogel technology to obtain porous particles with advanced performance in pulmonary delivery.

Semi-mechanistic PK/PD model to assess pulmonary targeting of beclomethasone dipropionate and its active metabolite

PURPOSE

The objective of this study was to describe the pulmonary targeting of beclomethasone dipropionate (BDP) and its active metabolite beclomethasone 17-monopropionate (BMP) in rats using a semi-mechanistic PK/PD model.

METHODS

Rat plasma and tissue concentrations of BDP and BMP, and tissue receptor occupancies of BMP after systemic and pulmonary delivery of BDP and BMP were integrated in a newly developed semi-mechanistic PK/PD model.

RESULTS

After IV administration of BDP, 95.4% of BDP was converted to BMP, while after pulmonary delivery of BDP, 46.6% of deposited BDP was absorbed as BMP. The developed semi-mechanistic PK model described plasma and tissue concentrations of BDP and BMP as well as receptor occupancies sufficiently well. The model incorporated dissolution, metabolic activation, and drug absorption processes to describe the local fate of BDP and BMP after systemic and pulmonary delivery. Dissolution rate constants of BDP and BMP were estimated to be 0.47/h and 2.01/h, respectively, and the permeabilities in central lung were estimated to be 15.0 and 2.9 × 10⁶ cm/s for BDP and BMP, respectively. The EC₅₀ of the binding of BMP to to the receptor was estimated to be 0.0017 ng/ml. Overall, receptor occupancies in the lung were more pronounced than those in the systemic circulation after pulmonary delivery of BDP or BMP. Simulations using the developed semi-mechanistic PK/PD model demonstrated that a slow dissolution rate and low permeability can improve pulmonary targeting.

CONCLUSIONS

A semi-mechanistic model was developed to describe the fate of an inhaled glucocorticoid pro-drug and its active metabolite in lung and the systemic circulation, both after pulmonary and systemic administration , thereby facilitating the understanding of the complex interplay between drug, prodrug and pharmacodynamic properties for quantifying the degree pulmonary targeting.

Nano-fats for bugs: the benefits of lipid nanoparticles for antimicrobial therapy

Bacterial infections are an imminent global healthcare threat evolving from rapidly advancing bacterial defence mechanisms that antibiotics fail to overcome. Antibiotics have been designed for systemic administration to target planktonic bacteria, leading to difficulties in reaching the site of localized bacterial infection and an inability to overcome the biological, chemical and physical barriers of bacteria, including biofilms, intracellular infections and antimicrobial resistance. The amphiphilic, biomimetic and antimicrobial properties of lipids provide a promising toolbox to innovate and advance antimicrobial therapies, overcoming the barriers presented by bacteria in order to directly and effectively treat recalcitrant infections. Nanoparticulate lipid-based drug delivery systems can enhance antibiotic permeation through the chemical and physical barriers of bacterial infections, as well as fuse with bacterial cell membranes, release antibiotics in response to bacteria and act synergistically with loaded antibiotics to enhance the total antimicrobial efficacy. This review explores the barriers presented by bacterial infections that pose bio-pharmaceutical challenges to antibiotics and how different structural and functional mechanisms of lipids can enhance antimicrobial therapies. Different nanoparticulate lipid-based systems are presented as valuable drug delivery systems to advance the efficacy of antibiotics, including liposomes, liquid crystalline nanoparticles, solid lipid nanoparticles, nanostructured lipid carriers and lipid nanocarriers. In summary, liquid crystalline nanoparticles are emerging with the greatest potential for clinical applications and commercial success as an "all-rounder" advanced lipid-based antimicrobial therapy that overcomes the multiple biological, chemical and physical barriers of bacteria.

Simulation of respiratory tract lining fluid for in vitro dissolution study

Introduction: Drug particles inhaled via the respiratory system must first dissolve in the respiratory tract lining fluid (RTLF) that lies on the surfaces of airways and alveoli, so that they are absorbed and have therapeutic action. Artificial simulated RTLFs are often used for in vitro dissolution studies to determine the solubility and dissolution of inhaled drug particles. Such studies can be used to predict bioavailability minimizing the requirement for in vivo studies. Numerous studies have been conducted to develop bio-relevant simulated RTLFs; however, to date, there is no singular simulated RTLF that closely resembles human RTLF.Areas covered: This review focuses on the composition of natural and simulated RTLFs and their use in in vitro dissolution studies.Expert opinion: There is variation in the composition and thickness of RTLF along the respiratory tract. Identification of the actual concentration of components of endogenous RTLF present in different areas of the respiratory tract helps in the development of region-specific simulated RTLFs. It is recommended that region-specific simulated RTLFs can be prepared by varying concentration of major RTLF components like mucus/gel simulants, lipids/surfactants, peptides/proteins, and inorganic/organic salts.

Model-Informed Drug Discovery and Development in Pulmonary Delivery: Biopharmaceutical Pharmacometric Modeling for Formulation Evaluation of Pulmonary Suspensions

For respiratory conditions, targeted drug delivery to the lungs could produce higher local concentrations with reduced risk of adverse events compared to systemic administration. Despite the increasing interest in pulmonary delivery, the pharmacokinetics (PK) of drugs following pulmonary administration remains to be elucidated. In this context, the application of modeling and simulation methodologies to characterize PK properties of compounds following pulmonary administration remains a scarcity. Pseudomonas aeruginosa (PA) lung infections are resistant to many of the current antibiotic therapies. Targeted treatments for pulmonary delivery could be particularly beneficial for these local conditions. In this study, we report the application of biopharmaceutical pharmacometrics (BPMX) for the analysis of PK data from three investigational antimicrobial agents following pulmonary administration of a suspension formulation. The observed drug concentration-time profiles in lungs and plasma of the compound series were combined for simultaneous analysis and modeling. The developed model describes the PK data, taking into account formulation properties, and provides a mechanism to predict dissolved drug concentrations in the lungs available for activity. The model was then used to evaluate formulation effects and the impact of variability on total and dissolved drug concentrations in lungs and plasma. The predictions suggest that these therapies for lung delivery should ideally be delivered in a sustained release formulation with high solubility for maximum local exposure in lungs for efficacy, with rapid systemic clearance in plasma for reduced risk of unwanted systemic adverse effects. This work shows the potential benefits of BPMX and the role it can play to support drug discovery and development in pulmonary delivery.

Contemporary Formulation Development for Inhaled Pharmaceuticals

Pulmonary delivery has gained increased interests over the past few decades. For respiratory conditions, targeted drug delivery directly to the site of action can achieve a high local concentration for efficacy with reduced systemic exposure and adverse effects. For systemic conditions, the unique physiology of the lung evolutionarily designed for rapid gaseous exchange presents an entry route for systemic drug delivery. Although the development of inhaled formulations has come a long way over the last few decades, many aspects of it remain to be elucidated. In particular, a reliable and well-understood method for in vitro-in vivo correlations remains to be established. With the rapid and ongoing advancement of technology, there is much potential to better utilise computational methods including different types of modelling and simulation approaches to support inhaled formulation development. This review intends to provide an introduction on some fundamental concepts in pulmonary drug delivery and inhaled formulation development followed by discussions on some challenges and opportunities in the translation of inhaled pharmaceuticals from preclinical studies to clinical development. The review concludes with some recent advancements in modelling and simulation approaches that could play an increasingly important role in modern formulation development of inhaled pharmaceuticals.

Comparison of the basic morphology and function of 3D lung epithelial cultures derived from several donors

In vitro models of the human lung play an essential role in evaluating the toxicity of inhaled compounds and understanding the development of respiratory diseases. Three-dimensional (3D) organotypic models derived from lung basal epithelial cells and grown at the air–liquid interface resemble human airway epithelium in multiple aspects, including morphology, cell composition, transcriptional profile, and xenobiotic metabolism. Whether the different characteristics of basal cell donors have an impact on model characteristics and responses remains unknown. In addition, studies are often conducted with 3D cultures from one donor, assuming a representative response on the population level. Whether this assumption is correct requires further investigation. In this study, we compared the morphology and functionality of 3D organotypic bronchial and small airway cultures from different donors at different weeks after air-lift to assess the interdonor variability in these parameters. The thickness, cell type composition, and transepithelial electrical resistance varied among the donors and over time after air-lift. Cilia beating frequency increased in response to isoproterenol treatment in both culture types, independent of the donor. The cultures presented low basal cytochrome P450 (CYP) 1A1/1B1 activity, but 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) treatment induced CYP1A1/1B1 activity regardless of the donor. In conclusion, lung epithelial cultures prepared from different donors present diverse morphology but similar functionality and metabolic activity, with certain variability in their response to stimulation.

•

3D lung cultures derived from various donors differed mostly at the morphological level.

•

Epithelial thickness, presence of cysts, ciliation, and goblet cell number are donor dependent.

•

Cilia beating frequency varied across donors but the response to isoproterenol was similar.

•

CYP450 activity in response to xenobiotics was preserved across donors.

Inter-compound and Intra-compound Global Sensitivity Analysis of a Physiological Model for Pulmonary Absorption of Inhaled Compounds

In recent years, global sensitivity analysis (GSA) has gained interest in physiologically based pharmacokinetics (PBPK) modelling and simulation from pharmaceutical industry, regulatory authorities, and academia. With the case study of an in-house PBPK model for inhaled compounds in rats, the aim of this work is to show how GSA can contribute in PBPK model development and daily use. We identified two types of GSA that differ in the aims and, thus, in the parameter variability: inter-compound and intra-compound GSA. The inter-compound GSA aims to understand which are the parameters that mostly influence the variability of the metrics of interest in the whole space of the drugs' properties, and thus, it is useful during the model development. On the other hand, the intra-compound GSA aims to highlight how much the uncertainty associated with the parameters of a given drug impacts the uncertainty in the model prediction and so, it is useful during routine PBPK use. In this work, inter-compound GSA highlighted that dissolution- and formulation-related parameters were mostly important for the prediction of the fraction absorbed, while the permeability is the most important parameter for lung AUC and MRT. Intra-compound GSA highlighted that, for all the considered compounds, the permeability was one of the most important parameters for lung AUC, MRT and plasma MRT, while the extraction ratio and the dose for the plasma AUC. GSA is a crucial instrument for the quality assessment of model-based inference; for this reason, we suggest its use during both PBPK model development and use.

Suitability and functional characterization of two Calu-3 cell models for prediction of drug permeability across the airway epithelial barrier

The Calu-3 cell line has been largely investigated as a physiological and pharmacological model of the airway epithelial barrier. Its suitability for prediction of drug permeability across the airway epithelia, however, has not been yet evaluated by using large enough set of model drugs. We evaluated two Calu-3 cell models (air-liquid and liquid-liquid) for drug permeability prediction based on the recent regulatory guidelines on showing suitability of in vitro permeability methods for drug permeability classification. Bidirectional permeability assays using 22 model drugs and several zero permeability markers, as well as using ABC transporter substrates were conducted. Functional activity of P-gp, but not of BCRP was revealed. The potential of the Calu-3 cells to be used as a model of the nasal epithelial barrier, despite their different anatomical origin, has been demonstrated by the obtained excellent correlation with the fully differentiated 3D human nasal epithelial model (MucilAir™) for 11 model drugs, as well as by the good correlation obtained with the human nasal epithelial cell line RPMI 2650. In addition, the permeability values determined in the two Calu-3 models correlated well with the intestinal permeability model Caco-2.

Post-inhalation cough with therapeutic aerosols: Formulation considerations

This review provides an assessment of post-inhalation cough with therapeutic aerosols. Factors that increase cough may be mitigated through design of the drug, formulation, and device. The incidence of cough is typically less than 5% for drugs with a nominal dose less than 1 mg, including asthma and COPD therapeutics. Cough increases markedly as the dose approaches 100 mg. This is due to changes in the composition of epithelial lining fluid (e.g., increases in osmolality, proton concentration). Whether an individual exhibits cough depends on their degree of sensitization to mechanical and chemical stimuli. Hypersensitivity is increased when the drug, formulation or disease result in increases in lung inflammation. Cough related to changes in epithelial lining fluid composition can be limited by using insoluble neutral forms of drugs and excipients.

Control of the Lung Residence Time of Highly Permeable Molecules after Nebulization: Example of the Fluoroquinolones

Pulmonary drug delivery is a promising strategy to treat lung infectious disease as it allows for a high local drug concentration and low systemic side effects. This is particularly true for low-permeability drugs, such as tobramycin or colistin, that penetrate the lung at a low rate after systemic administration and greatly benefit from lung administration in terms of the local drug concentration. However, for relatively high-permeable drugs, such as fluoroquinolones (FQs), the rate of absorption is so high that the pulmonary administration has no therapeutic advantage compared to systemic or oral administration. Formulation strategies have thus been developed to decrease the absorption rate and increase FQs’ residence time in the lung after inhalation. In the present review, some of these strategies, which generally consist of either decreasing the lung epithelium permeability or decreasing the release rate of FQs into the epithelial lining fluid after lung deposition, are presented in regards to their clinical aspects.

Pharmacokinetic profile analyses for inhaled drugs in humans using the lung delivery and disposition model

The kinetic clarification of lung disposition for inhaled drugs in humans via pharmacokinetic (PK) modeling aids in their development and regulation for systemic and local delivery, but remains challenging due to its multiplex nature. This study exercised our lung delivery and disposition kinetic model to derive the kinetic descriptors for the lung disposition of four drugs [calcitonin, tobramycin, ciprofloxacin and fluticasone propionate (FP)] inhaled via different inhalers from the published PK profile data. With the drug dose delivered to the lung (DTL) estimated from the corresponding γ-scintigraphy or in vivo predictive cascade impactor data, the model-based curve-fitting and statistical moment analyses derived the rate constants of lung absorption (k_a ) and non-absorptive disposition (k_nad ). The k_a values differed substantially between the drugs (0.05-1.00 h^-1 ), but conformed to the lung partition-based membrane diffusion except for FP, and were inhaler/delivery/deposition-independent. The k_nad values also varied widely (0.03-2.32 h^-1 ), yet appeared to be explained by the presence or absence of non-absorptive disposition in the lung via mucociliary clearance, local tissue degradation, binding/sequestration and/or phagocytosis, and to be sensitive to differences in lung deposition. For FP, its k_a value of 0.2 h^-1 was unusually low, suggesting solubility/dissolution-limited slow lung absorption, but was comparable between two inhaler products. Thus, the difference in the PK profile was attributed to differences in the DTL and the k_nad value, the latter likely originating from different aerosol sizes and regional deposition in the lung. Overall, this empirical, rather simpler model-based analysis provided a quantitative kinetic understanding of lung absorption and non-absorptive disposition for four inhaled drugs from PK profiles in humans.

Aerosolization Performance of Jet Nebulizers and Biopharmaceutical Aspects

In this work, 13 jet nebulizers, some of which in different configurations, were investigated in order to identify the biopharmaceutical constraints related to the quality attributes of the medicinal products, which affect their safety, efficiency, compliance, and effectiveness. The aerosolization parameters, including the aerosol output, aerosol output rate, mass median aerodynamic diameter, and fine particle fraction, were determined according to the European Standard EN 13544-1, using sodium fluoride as a reference formulation. A comparison between the aerosol output nebulization time and the fine particle fraction displayed a correlation between the aerosol quality and the nebulization rate. Indeed, the quality of the nebulization significantly increased when the rate of aerosol emission was reduced. Moreover, the performance of the nebulizers was analyzed in terms of respirable delivered dose and respirable dose delivery rate, which characterize nebulization as the rate and amount of respirable product that could be deposited into the lungs. Depending on which of these two latter parameters was used, the nebulizers showed different performances. The differences, in terms of the rate and amount of delivered aerosol, could provide relevant information for the appropriate choice of nebulizer as a function of drug product, therapy, and patient characteristics.

Use of PBPK Modeling To Evaluate the Performance of Dissolv It, a Biorelevant Dissolution Assay for Orally Inhaled Drug Products

The dissolution of inhaled drug particles in the lungs is a challenge to model using biorelevant methods in terms of (i) collecting a respirable emitted aerosol fraction and dose, (ii) presenting this to a small volume of medium that is representative of lung lining fluid, and (iii) measuring the low concentrations of drug released. We report developments in methodology for each of these steps and utilize mechanistic in silico modeling to evaluate the in vitro dissolution profiles in the context of plasma concentration–time profiles. The PreciseInhale aerosol delivery system was used to deliver Flixotide aerosol particles to DissolvIt apparatus for measurement of dissolution. Different media were used in the DissolvIt chamber to investigate their effect on dissolution profiles, these were (i) 1.5% poly(ethylene oxide) with 0.4% l-alphaphosphatidyl choline, (ii) Survanta, and (iii) a synthetic simulated lung lining fluid (SLF) based on human lung fluid composition. For fluticasone proprionate (FP) quantification, solid phase extraction was used for sample preparation with LC–MS/MS analysis to provide an assay that was fit for purpose with a limit of quantification for FP of 312 pg/mL. FP concentration–time profiles in the flow-past perfusate were similar irrespective of the medium used in the DissolvIt chamber (∼0.04–0.07%/min), but these were significantly lower than transfer of drug from air-to-perfusate in isolated perfused lungs (0.12%/min). This difference was attributed to the DissolvIt system representing slower dissolution in the central region of the lungs (which feature nonsink conditions) compared to the peripheral regions that are represented in the isolated lung preparation. Pharmacokinetic parameters (C_max, T_max, and AUC_0-∞) were estimated from the profiles for dissolution in the different lung fluid simulants and were predicted by the simulation within 2-fold of the values reported for inhaled FP (1000 μg dose) administered via Flixotide Evohaler 250 μg strength inhaler in man. In conclusion, we report methods for performing biorelevant dissolution studies for orally inhaled products and illustrate how they can provide inputs parameters for physiologically based pharmacokinetic (PBPK) modeling of inhaled medicines.

Models of deposition, pharmacokinetics, and intersubject variability in respiratory drug delivery

INTRODUCTION

Aerosol drug delivery to the lungs via inhalation is widely used in the treatment of respiratory diseases. The deposition pattern of inhaled particles within the airways of the respiratory tract is key in determining the initial delivered dose. Thereafter, dose-dependent processes including drug release or dissolution, clearance, and absorption influence local and systemic exposure to inhaled drugs over time.

AREAS COVERED

Empirical correlations, numerical simulation, and in vitro airway geometries that permit improved prediction of extrathoracic and lung deposition fractions in a variety of age groups and breathing conditions are described. Efforts to link deposition models with pharmacokinetic models predicting lung and systemic exposure to inhaled drugs over time are then reviewed. Finally, new methods to predict intersubject variability in extrathoracic deposition, capturing variability in both size and shape of the upper airways, are highlighted.

EXPERT OPINION

Recent work has been done to expand in vitro deposition experiments to a wide range of age groups and breathing conditions, to link regional lung deposition models with pharmacokinetic models, and to improve prediction of intersubject variability. These efforts are improving predictive understanding of respiratory drug delivery, and will aid the development of new inhaled drugs and delivery devices.