Comparison of deposition in the USP and physical mouth-throat models with solid and liquid particles

The impact of actuator nozzle and surroundings condition on drug delivery using pressurized-metered dose inhalers

The most commonly used method to deliver aerosolized drugs to the lung is with pressurized metered-dose inhalers (pMDIs). The spray actuator is a critical component of pMDI, since it controls the atomization process by forming aerosol plumes and determining droplet size distribution. Through computational fluid dynamics (CFD) simulations, this study investigated the effect of two different nozzle types (single conventional and twin nozzles) on drug deposition in the mouth-throat (MT) region. We also studied the behavior of aerosol plumes in both an open-air environment and the MT geometry. Our study revealed that spray aerosol generated in an unconfined, open-air environment with no airflow behaves distinctly from spray introduced into the MT geometry in the presence of airflow. In addition, the actuator structure significantly impacts the device's efficacy. In the real MT model, we found that the twin nozzle increases drug deposition in the MT region, and its higher aerosol velocity negatively affects its efficiency.

An experimental study on lung deposition of inhaled 2 μm particles in relation to lung characteristics and deposition models

BACKGROUND

The understanding of inhaled particle respiratory tract deposition is a key link to understand the health effects of particles or the efficiency for medical drug delivery via the lung. However, there are few experimental data on particle respiratory tract deposition, and the existing data deviates considerably when comparing results for particles > 1 μm.

METHODS

We designed an experimental set-up to measure deposition in the respiratory tract for particles > 1 μm, more specifically 2.3 μm, with careful consideration to minimise foreseen errors. We measured the deposition in seventeen healthy adults (21-68 years). The measurements were performed at tidal breathing, during three consecutive 5-minute periods while logging breathing patterns. Pulmonary function tests were performed, including the new airspace dimension assessment (AiDA) method measuring distal lung airspace radius (rAiDA). The lung characteristics and breathing variables were used in statistical models to investigate to what extent they can explain individual variations in measured deposited particle fraction. The measured particle deposition was compared to values predicted with whole lung models. Model calculations were made for each subject using measured variables as input (e.g., breathing pattern and functional residual capacity).

RESULTS

The measured fractional deposition for 2.3 μm particles was 0.60 ± 0.14, which is significantly higher than predicted by any of the models tested, ranging from 0.37 ± 0.08 to 0.53 ± 0.09. The multiple-path particle dosimetry (MPPD) model most closely predicted the measured deposition when using the new PNNL lung model. The individual variability in measured particle deposition was best explained by breathing pattern and distal airspace radius (rAiDA) at half inflation from AiDA. All models underestimated inter-subject variability even though the individual breathing pattern and functional residual capacity for each participant was used in the model.

CONCLUSIONS

Whole lung models need to be tuned and improved to predict the respiratory tract particle deposition of micron-sized particles, and to capture individual variations - a variation that is known to be higher for aged and diseased lungs. Further, the results support the hypothesis that the AiDA method measures dimensions in the peripheral lung and that rAiDA, as measured by the AiDA, can be used to better understand the individual variation in the dose to healthy and diseased lungs.

Computational investigation of flow characteristics and particle deposition patterns in a realistic human airway model under different breathing conditions

Airborne particle pollution causes a range of respiratory and cardiovascular disorders by entering the human respiratory system through the breathing process. The administration of pharmaceutical particles by inhalation is another effective way to treat pulmonary illnesses. Studying particle deposition in the respiratory system during human breathing is crucial to maintaining human health. This necessity served as the impetus for this work, which aims to investigate how the airflow and particles' deposition are influenced by constant inhalation and circulatory breathing, particle diameter, and changes in airflow rate. The focus of this paper is to compare the particle deposition results of circulatory respiration with constant respiration. Based on computed tomography (CT) scan pictures, a precise human airway model from the mouth cavity to the fifth-generation bronchi was created. Flow fields and particle deposition inside the respiratory tract were examined at varied breathing rates (30, 60, and 90L/min of constant and circulatory breathing) and varying haled particle sizes (5 and 10 μm). The results showed that the oropharyngeal area is often where the majority of particles are deposited. The particle distribution fraction is more significant in the bronchial area than the oropharyngeal region due to lower inhalation velocities and smaller particle sizes. For particles with a diameter of 5µm, constant respiration and circulatory respiration have virtually identical particle distribution fractions in each region. For particles with a diameter of 10µm, the particle distribution fraction for circulatory respiration is slightly higher than for constant respiration in the bronchial region as the flow rate increases. For both constant and circulatory respiration, particles are deposited more in the right lung and less in the left. These results contribute to further research on respiratory diseases caused by inhaled particles and guide inhalation therapy for better treatment outcomes.

Deconvolution of Systemic Pharmacokinetics Predicts Inhaled Aerosol Dosimetry of Nicotine

Absorption of inhaled compounds can occur from multiple sites based on upper and lower respiratory tract deposition, and clearance mechanisms leading to differential local and systemic pharmacokinetics. Deriving inhaled aerosol dosimetry and local tissue concentrations for nose-only exposure in rodents and inhaled products in humans is challenging. In this study we use inhaled nicotine as an example to identify regional respiratory tract deposition, absorption fractions, and their contribution toward systemic pharmacokinetics in rodents and humans. A physiologically based pharmacokinetic (PBPK) model was constructed to describe the disposition of nicotine and its major metabolite, cotinine. The model description for the lungs was simplified to include an upper respiratory tract region with active mucociliary clearance and a lower respiratory tract region. The PBPK model parameters such as rate of oral absorption, metabolism and clearance were fitted to the published nicotine and cotinine plasma concentrations post systemic administration and oral dosing. The fractional deposition of inhaled aerosol in the upper and lower respiratory tract regions was estimated by fitting the plasma concentrations. The model predicted upper respiratory tract deposition was 63.9% for nose-only exposure to nicotine containing nebulized aqueous aerosol in rats and 60.2% for orally inhaled electronic vapor product in humans. A marked absorption of nicotine from the upper respiratory tract and the gastrointestinal tract for inhaled aqueous aerosol contributed to the differential systemic pharmacokinetics in rats and humans. The PBPK model derived dosimetry shows that the current aerosol dosimetry models with their posteriori application using independent aerosol physicochemical characterization to predict aerosol deposition are insufficient and will need to consider complex interplay of inhaled aerosol evolutionary process. While the study highlights the needs for future research, it provides a preliminary framework for interpreting pharmacokinetics of inhaled aerosols to facilitate the analysis of in vivo exposure-responses for pharmacological and toxicological assessments.

Flow Patterns and Particle Residence Times in the Oral Cavity during Inhaled Drug Delivery

Pulmonary drug delivery aims to deliver particles deep into the lungs, bypassing the mouth−throat airway geometry. However, micron particles under high flow rates are susceptible to inertial impaction on anatomical sites that serve as a defense system to filter and prevent foreign particles from entering the lungs. The aim of this study was to understand particle aerodynamics and its possible deposition in the mouth−throat airway that inhibits pulmonary drug delivery. In this study, we present an analysis of the aerodynamics of inhaled particles inside a patient-specific mouth−throat model generated from MRI scans. Computational Fluid Dynamics with a Discrete Phase Model for tracking particles was used to characterize the airflow patterns for a constant inhalation flow rate of 30 L/min. Monodisperse particles with diameters of 7 μm to 26 μm were introduced to the domain within a 3 cm-diameter sphere in front of the oral cavity. The main outcomes of this study showed that the time taken for particle deposition to occur was 0.5 s; a narrow stream of particles (medially and superiorly) were transported by the flow field; larger particles > 20 μm deposited onto the oropharnyx, while smaller particles < 12 μm were more disperse throughout the oral cavity and navigated the curved geometry and laryngeal jet to escape through the tracheal outlet. It was concluded that at a flow rate of 30 L/min the particle diameters depositing on the larynx and trachea in this specific patient model are likely to be in the range of 7 μm to 16 μm. Particles larger than 16 μm primarily deposited on the oropharynx.

Characterization of dry powder inhaler performance through experimental methods

Experimental methods provide means for the quality control of existing DPIs and for exploring the influence of formulation and device parameters well in advance of clinical trials for novel devices and formulations. In this review, we examine the state of the art of in vitro testing of DPIs, with a focus primarily on the development of accurate in vitro-in vivo correlations. Aspects of compendial testing are discussed, followed by the influence of flow profiles on DPI performance, the characterization of extrathoracic deposition using mouth-throat geometries, and the characterization of regional thoracic deposition. Additional experimental methods that can inform the timing of bolus delivery, the influence of environmental conditions, and the development of electrostatic charge on aerosolized DPI powders are reviewed. We conclude with perspectives on current in vitro methods and identify potential areas for future investigation, including the estimation of variability in deposition, better characterization of existing compendial methods, optimization of formulation and device design to bypass extrathoracic deposition, and the use of novel tracheobronchial filters that aim to provide more clinically relevant measures of performance directly from in vitro testing.

Simulating the effect of individual upper airway anatomical features on drug deposition

This study aims to systematically isolate different anatomical features of the human pharynx with the goal to investigate their independent influence on airflow dynamics and particle deposition characteristics in a geometrically realistic human airway. Specifically, the effects of the uvula, epiglottis and soft palate on drug particle deposition are studied systematically, by carefully removing each of these anatomical features from reconstructed models based on MRI data and comparing them to a benchmark realistic airway model. Computational Fluid Dynamics using established turbulence models is employed to simulate the transport of mono-dispersed particles (3 µm) in the airway at two flow-rates. The simulations suggest three findings: 1) widening the space between the oral cavity and oropharynx and where the soft palate is situated leads to the most dramatic reduction in drug deposition in the upper airway; 2) exclusion of the uvula and epiglottis: a) affects flow dynamics in the airway; b) alters regional deposition behaviour; c) does not significantly affect the total number of particles deposited in the pharynx; and 3) the space adjacent to the soft palate is a key determinant for aerosol deposition in the extrathoracic region and is related to mechanisms of flow acceleration, diversion and recirculation.

In Vitro and In Silico Investigations on Drug Delivery in the Mouth-Throat Models with Handihaler®

This work aimed to evaluate the relative inhalation parameters that affect the deposition of inhaled aerosols, including mouth-throat morphology, airflow rate, and initial condition of emitted particles. In vitro experiments were conducted using the US Pharmacopeia (USP) throat and a realistic mouth-throat (RMT) with Handihaler®. Then, in silico study of the gas-solid flow was performed by computational fluid dynamics and discrete phase method. Results indicated that aerosol deposition in RMT was higher compared to that in USP throat at an airflow rate of 30 L/min, with 33.16 ± 7.84% and 21.11 ± 7.1% lung deposition in USP throat and RMT models, respectively, which showed a better correlation with in vivo data from the literature. Increasing airflow rate resulted in better drug aerosolization, while the fine particle dose trend ascended before declining, with the peak value obtained at a flow rate of 40 L/min. Overall, the effect of geometrical variation was more significant. Additionally, in silico results demonstrated clearly that the initial conditions of the emitted particles from inhalers affected the subsequent deposition. Larger momentum possessed by the central aerosol jet entering the mouth directly led to stronger impaction, which resulted in the deposition in the front region of mouth-throat models. This study is beneficial to develop an in silico method to understand the underlying mechanisms of in vivo mouth-throat deposition.

Lower Inspiratory Breathing Depth Enhances Pulmonary Delivery Efficiency of ProAir Sprays

Effective pulmonary drug delivery using a metered-dose inhaler (MDI) requires a match between the MDI sprays, the patient’s breathing, and respiratory physiology. Different inhalers generate aerosols with distinct aerosol sizes and speeds, which require specific breathing coordination to achieve optimized delivery efficiency. Inability to perform the instructed breathing maneuver is one of the frequently reported issues during MDI applications; however, their effects on MDI dosimetry are unclear. The objective of this study is to systemically evaluate the effects of breathing depths on regional deposition in the respiratory tract using a ProAir-HFA inhaler. An integrated inhaler mouth-throat-lung geometry model was developed that extends to the ninth bifurcation (G9). Large-eddy simulation (LES) was used to compute the airflow dynamics due to concurrent inhalation and orifice flows. The discrete-phase Lagrangian model was used to track droplet motions. Experimental measurements of ProAir spray droplet sizes and speeds were used as initial and boundary conditions to develop the computational model for ProAir-pulmonary drug delivery. The time-varying spray plume from a ProAir-HFA inhaler into the open air was visualized using a high-speed imaging system and was further used to validate the computational model. The inhalation dosimetry of ProAir spray droplets in the respiratory tract was compared among five breathing depths on a regional, sub-regional, and local basis. The results show remarkable differences in airflow dynamics within the MDI mouthpiece and the droplet deposition distribution in the oral cavity. The inhalation depth had a positive relationship with the deposition in the mouth and a negative relationship with the deposition in the five lobes beyond G9 (small airways). The highest delivery efficiency to small airways was highest at 15 L/min and declined with an increasing inhalation depth. The drug loss inside the MDI was maximal at 45–60 L/min. Comparisons to previous experimental and numerical studies revealed a high dosimetry sensitivity to the inhaler type and patient breathing condition. Considering the appropriate inhalation waveform, spray actuation time, and spray properties (size and velocity) is essential to accurately predict inhalation dosimetry from MDIs. The results highlight the importance of personalized inhalation therapy to match the patient’s breathing patterns for optimal delivery efficiencies. Further complimentary in vitro or in vivo experiments are needed to validate the enhanced pulmonary delivery at 15 L/min.

A filter-based system mimicking the particle deposition and penetration in human respiratory system for secondhand smoke generation and characterization

INTRODUCTION

Secondhand smoke endangers both the environment and the health of nonsmokers. Due to the scarcity of repeatable data generated by human subjects, a system capable of generating representative secondhand smoke is essential for studying smoke properties. This work presents the design and validation of a filter-based system that could mimic the particle deposition and penetration in human respiratory system for secondhand smoke generation and characterization.

METHODS

Guided by our study on characterizing size-dependent filtration efficiency of common materials, we identified three filter media that generate similar particle deposition efficiencies compared to different regions of the human respiratory system over a wide submicron size range. We demonstrated the performance of the proposed filter-based system using various operating conditions. Additionally, we compared the properties of secondhand smoke particles to those of primary smoke particles.

RESULTS

The difference in aerosol deposition efficiencies between the filter-based system and the International Commission on Radiological Protection (ICRP) model was less than 10% in the size range of 30 to 500 nm. High concentrations of metals were detected in the secondhand smoke. The contents of Ni and Cr generated from the secondhand electronic cigarettes are at least 20 and 5 times above the regulated daily maximum intake amount.

CONCLUSION

Given the agreement in aerosol respiratory deposition between the filter-based system and the ICRP model, such a system can facilitate laboratory studies of secondhand smoke due to its simple structure, high repeatability, and ease of control while remaining free of human subjects.

Use of Airway Replicas in Lung Delivery Applications

The use of extrathoracic airway replicas in optimization of drug delivery to the lungs with nebulizers, dry powder inhalers (DPIs) and pressurized metered-dose inhalers (pMDIs) is discussed. Such airway replicas have been useful in evaluating new pulmonary drug delivery platforms mainly based on the comparison of the total lung dose (TLD) and the aerodynamic particle size distribution (APSD) of the aerosol distal to the physical models. The ability of these in vitro methods to replicate in vivo results has allowed advancements in respiratory drug delivery and in the accuracy and utility of in vitro-in vivo correlations (IVIVCs).

Computational investigation of particle penetration and deposition pattern in a realistic respiratory tract model from different types of dry powder inhalers

The aim of this study was to evaluate the device performance of a new design by comparing with a typical commercial DPI. Computational fluid dynamics (CFD) coupled with the discrete element method (DEM) collision has been utilized in this study to characterize and examine the flow field and particle transportation, respectively. A typical commercial DPI and an in-house designed novel DPI with distinct design features were compared to explore their dispersion capabilities and suitability for delivery to the respiratory tract. For this exploration, realistic oral to larynx and tracheobronchial airway models consisting of bio-relevant features were adopted to enhance practical feasibility. Distinct aerosol performances were observed between the two DPIs in the respiratory tract, where the in-house DPI, in comparison with the commercial DPI, has shown approximately 30% lower deposition fraction in the mouth-throat region with approximately 7% higher escape rate in the tracheobronchial region under the identical inhalation condition. This observation demonstrates that a novel in-house designed DPI provides higher device efficiency over the selected typical commercial DPI.

Targeting of Inhaled Therapeutics to the Small Airways: Nanoleucine Carrier Formulations

Current dry powder formulations for inhalation deposit a large fraction of their emitted dose in the upper respiratory tract where they contribute to off-target adverse effects and variability in lung delivery. The purpose of the current study is to design a new formulation concept that more effectively targets inhaled dry powders to the large and small airways. The formulations are based on adhesive mixtures of drug nanoparticles and nanoleucine carrier particles prepared by spray drying of a co-suspension of leucine and drug particles from a nonsolvent. The physicochemical and aerosol properties of the resulting formulations are presented. The formulations achieve 93% lung delivery in the Alberta Idealized Throat model that is independent of inspiratory flow rate and relative humidity. Largely eliminating URT deposition with a particle size larger than solution pMDIs is expected to improve delivery to the large and small airways, while minimizing alveolar deposition and particle exhalation.

Using Filters to Estimate Regional Lung Deposition with Dry Powder Inhalers

PURPOSE

To develop an in vitro method to rapidly evaluate regional lung doses delivered by pharmaceutical inhalers. Currently, cascade impactor measurements are used, but these are resource intensive and require significant post processing of in vitro data to arrive at regional deposition estimates.

METHODS

We present a specialized filter apparatus that mimics tracheobronchial (TB) deposition of pharmaceutical aerosols emitted by commercially available dry powder inhalers (DPIs). The filter housing includes an electrostatic neutralizer to eliminate artificial electrostatic filtration effects. Regional deposition (tracheobronchial and alveolar) for four DPIs (Onbrez Breezhaler, Flovent Diskus, Pulmicort Turbuhaler, and Asmanex Twisthaler) was estimated using cascade impactor measurements and an in silico regional deposition model. These estimates were compared to direct measurements of regional deposition as provided by the TB filter mimic and an absolute filter placed downstream of the TB filter housing, representing the alveolar dose.

RESULTS

The two methods were shown to provide similar estimates of extrathoracic, tracheobronchial, and alveolar deposition, as well as total recovery of active pharmaceutical ingredients.

CONCLUSIONS

Because of its design, the TB filter apparatus makes it possible to estimate regional deposition with inhalers directly using variable inhalation profiles without any additional equipment or changes to the experimental configuration. This method may be useful to expedite development of both innovative and generic drug products as it provides regional respiratory tract deposition estimates using fewer resources than exisiting methods.

Bioequivalence assessment of pharmaceutical aerosol products through IVIVC

Many pharmaceutical developers of generic orally inhaled products (OIPs) are facing significant issues in passing the regulatory requirement to show pharmacokinetic (PK) bioequivalence (BE) to the originator product. The core of the issue is that no reliable in vitro-in vivo correlation (IVIVC) is available to guide their development. In this paper, several issues are identified and means to improve the data used for developing an IVIVC are discussed. The article also presents an "IVIVC-free" approach for developing a formulation matching the originator's PK performance.

Evaluation of the stability of a spray-dried tuberculosis vaccine candidate designed for dry powder respiratory delivery

Particle engineering via spray drying was used to develop a dry powder presentation of an adjuvanted tuberculosis vaccine candidate. This presentation utilizing a trileucine-trehalose excipient system was designed to be both thermostable and suitable for respiratory delivery. The stability of the spray-dried vaccine powder was assessed over one year at various storage temperatures (-20, 5, 25, 40, 50 °C) in terms of powder stability, adjuvant stability, and antigen stability. A formulation without trileucine was included as a control. The results showed that the interior particle structure and exterior particle morphology of the powder was maintained for one year at 40 °C, while the control case exhibited a small extent of particle fusing under the same storage conditions. Moisture content was maintained, and powder solid state remained amorphous for all storage temperatures. Aerosol performance was assessed with a commercial dry powder inhaler in combination with a human mouth-throat model. The emitted dose and lung dose were maintained for all samples after one year at temperatures up to 40 °C. Nanoemulsion size and oil content of the adjuvant system were maintained after one year at temperatures up to 40 °C, and the agonist content was maintained after one year at temperatures up to 25 °C. The antigen was completely degraded in the control formulation at seven months of storage at 40 °C; by contrast, 45% of the antigen was still present in the trehalose-trileucine formulation after one year of storage at 50 °C. Comparatively, the antigen was completely degraded in a liquid sample of the vaccine candidate after only one month of storage at 37 °C. The spray-dried trehalose-trileucine vaccine powder clearly maintained its inhalable properties after one year's storage at high temperatures and improved overall thermostability of the vaccine.

Role of CFD based in silico modelling in establishing an in vitro-in vivo correlation of aerosol deposition in the respiratory tract

Effective evaluation and prediction of aerosol transport deposition in the human respiratory tracts are critical to aerosol drug delivery and evaluation of inhalation products. Establishment of an in vitro-in vivo correlation (IVIVC) requires the understanding of flow and aerosol behaviour and underlying mechanisms at the microscopic scale. The achievement of the aim can be facilitated via computational fluid dynamics (CFD) based in silico modelling which treats the aerosol delivery as a two-phase flow. CFD modelling research, in particular coupling with discrete phase model (DPM) and discrete element method (DEM) approaches, has been rapidly developed in the past two decades. This paper reviews the recent development in this area. The paper covers the following aspects: geometric models of the respiratory tract, CFD turbulence models for gas phase and its coupling with DPM/DEM for aerosols, and CFD investigation of the effects of key factors associated with geometric variations, flow and powder characteristics. The review showed that in silico study based on CFD models can effectively evaluate and predict aerosol deposition pattern in human respiratory tracts. The review concludes with recommendations on future research to improve in silico prediction to achieve better IVIVC.

Development of a formulation platform for a spray-dried, inhalable tuberculosis vaccine candidate

Protection against primarily respiratory infectious diseases, such as tuberculosis (TB), can likely be enhanced through mucosal immunization induced by direct delivery of vaccines to the nose or lungs. A thermostable inhalable dry powder vaccine offers further advantages, such as independence from the cold chain. In this study, we investigate the formulation for a stable, inhalable dry powder version of ID93 + GLA-SE, an adjuvanted subunit TB vaccine candidate, containing recombinant fusion protein ID93 and glucopyranosyl lipid A (GLA) in a squalene emulsion (SE) as an adjuvant system, via spray drying. The addition of leucine (20% w/w), pullulan (10%, 20% w/w), and trileucine (3%, 6% w/w) as dispersibility enhancers was investigated with trehalose as a stabilizing agent. Particle morphology and solid state, nanoemulsion droplet size, squalene and GLA content, ID93 presence, and aerosol performance were assessed for each formulation. The results showed that the addition of leucine improved aerosol performance, but increased aggregation of the emulsion droplets was demonstrated on reconstitution. Addition of pullulan preserved emulsion droplet size; however, the antigen could not be detected after reconstitution. The trehalose-trileucine excipient formulations successfully stabilized the adjuvant system, with evidence indicating retention of the antigen, in an inhalable dry powder format suitable for lung 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.

Addressing the Need for Controls on Particle Bounce and Re-entrainment in the Cascade Impactor and for the Mitigation of Electrostatic Charge for Aerodynamic Particle Size Assessment of Orally Inhaled Products: an Assessment by the International Consortium on Regulation and Science (IPAC-RS)

Multi-stage cascade impactors (CI) are accepted for the determination of metrics of the drug mass aerodynamic particle size distributions (APSD) of aerosols emitted from orally inhaled products (OIPs). This is particularly important for products where the drug to excipient ratio or particle density may not be the same in each aerodynamic size fraction; examples of such products are carrier-containing dry powder inhalers (DPIs) and suspension pressurized metered-dose inhalers (pMDIs). CI measurements have been used as the "gold standard" for acceptance of alternative methods of APSD assessment, such as laser diffraction for nebulized solutions. Although these apparatus are labor-intensive, they are accepted in regulatory submissions and quality control assessments because the mass of active pharmaceutical ingredient(s) in the aerosol can be quantified by chemical assay and measured particle size is based on the aerodynamic diameter scale that is predictive of deposition in the respiratory tract. Two of the most important factors that modify the ideal operation of an impactor are "particle bounce," that is often accompanied by re-entrainment in the air flow passing the stage of interest, and electrostatic charge acquired by the particles during the preparation and aerosolization of the formulation when the inhaler is actuated. This article reviews how both factors can lead to biased APSD measurements, focusing on measurements involving pMDIs and DPIs, where these sources of error are most likely to be encountered. Recommendations are provided for the mitigation of both factors to assist the practitioner of these measurements.

Cascade Impactor Performance of Commercial pMDI Formulations Using Modified Induction Ports

The induction port (IP) for aerosol analysis with the Next Generation Pharmaceutical Impactor as monographed in the United States and European pharmacopoeia (USPIP) lacks physiological relevance, which, amongst other reasons, has been identified as critical for the predictability of in vitro aerosol data to lung deposition observed in vivo. In this publication, we report the impact of replacing the USPIP with two modified induction ports, which were designed based around geometries derived from a computer tomographic scan of a human trachea and the distal section of the USPIP. Test formulations were selected on the basis of availability of in vivo lung deposition data so that results obtained in vitro could be evaluated for their predictability. All formulations assessed showed increased deposition in the modified induction ports, and different mechanisms of particle deposition have been identified. In vitro predictions of the lung deposition were found to correlate well with the in vivo observations reported using the modified induction ports. Furthermore, the quality of the correlation was found superior to the one achieved with the USPIP with an average deviation of the predicted from observed values (n = 10) of 6 ± 4, 12 ± 6, and 16 ± 6% for the modified induction ports (mIP and mIPext) and the USPIP, respectively, when using a fine particle fraction (FPF) cutoff value of 5 μm. Using a FPF cutoff value of 3 μm yielded a more accurate in vitro-in vivo correlation with an average deviation of the predicted from observed values of 5 ± 4, 7 ± 5, and 8 ± 4% for the mIP, mIPext, and USPIP, respectively. For both FPF size cutoff values, the mIP yielded the most accurate in vitro-in vivo correlation.

Does upper airway deformation affect drug deposition?

Knowledge that enables the accurate simulation of drug deposition in the human upper airway is necessary to develop robust platforms for efficient drug delivery by inhalation devices. The human upper airway is deformable during inhalation but how it could affect the deposition of inhaled drugs is unknown. We aimed to determine whether pharyngeal deformation at the soft palate level would have any significant effects on throat deposition, in vitro lung dose and fine particle fraction. In this study, dry mannitol powders were delivered to the next-generation cascade impactor (NGI) through the United States Pharmacopeia (USP) throat, and a realistic upper airway cast (RUPAC) at flow rates of 40, 60 and 80 L min^-1. Deformation of the upper airway at 25%, 50%, and 75% in the lateral and antero-posterior directions were experimentally simulated in the RUPAC. Throat deposition (p = 0.04) is significantly affected when the upper airway deforms laterally but not antero-posteriorly.

Use of inspiratory profiles from patients with chronic obstructive pulmonary disease (COPD) to investigate drug delivery uniformity and aerodynamic dose emission of indacaterol from a capsule based dry powder inhaler

Most patients using dry powder inhalers (DPIs) are unable to achieve the inhalation parameters recommended for pharmacopoeial in-vitro dose emission testing. The dose emission characteristics of indacaterol Breezhaler (IB) have been measured using COPD patients' inhalation profiles (IPs) when using IB and replayed in-vitro using a breath simulator attached to an Andersen Cascade Impactor. The peak inhalation flow (PIF) of the profiles ranged from 28.3 to 87.8 L/min and inhaled volumes (Vin) from 0.7 to 3 L. The indacaterol total emitted doses (TED), fine particle dose (FPD) and mass median aerodynamic diameter (MMAD) were measured. TED varied between 61% to 83% of the 150 μg nominal dose, the FPD was found to vary between 19% and 30% and the MMAD from 3.7 μm to 2.3 μm with the increase of the profiles' PIF and Vin. The mean (SD) values were 113.4(8.9) μg, 39.7(5.0) μg and 2.7(0.5) μm, respectively. The quantity and the quality of the emitted dose from the indacaterol Breezhaler® are dependent on the capability of a patient generating an optimal inhalation profile. Therefore, when using the IB patients should be encouraged to inhale as fast as they can from the start of their inhalation and for as long as possible.

Biophysical model to predict lung delivery from a dual bronchodilator dry-powder inhaler

A biophysical lung model was designed to predict inhaled drug deposition in patients with obstructive airway disease, and quantitatively investigate sources of deposition variability. Different mouth-throat anatomies at varying simulated inhalation flows were used to calculate the lung dose of indacaterol/glycopyrronium [IND/GLY] 110/50 µg (QVA149) from the dry-powder inhaler Breezhaler^®. Sources of variability in lung dose were studied using computational fluid dynamics, supported by aerosol particle sizing measurements, particle image velocimetry and computed tomography. Anatomical differences in mouth-throat geometries were identified as a major source of inter-subject variability in lung deposition. Lung dose was similar across inhalation flows of 30–120 L/min with a slight drop in calculated delivery at high inspiratory flows. Delivery was relatively unaffected by inhaler inclination angle. The delivered lung dose of the fixed-dose combination IND/GLY matched well with corresponding monotherapy doses. This biophysical model indicates low extra-thoracic drug loss and consistent lung delivery of IND/GLY, independent of inhalation flows. This is an important finding for patients across various ages and lung disease severities. The model provides a quantitative, mechanistic simulation of inhaled therapies that could provide a test system for estimating drug delivery to the lung and complement traditional clinical studies.

Determination of Passive Dry Powder Inhaler Aerodynamic Particle Size Distribution by Multi-Stage Cascade Impactor: International Pharmaceutical Aerosol Consortium on Regulation & Science (IPAC-RS) Recommendations to Support Both Product Quality Control and Clinical Programs

The multi-stage cascade impactor (CI) is the mainstay method for the determination of the aerodynamic particle size distribution (APSD) of aerosols emitted from orally inhaled products (OIPs). CIs are designed to operate at a constant flow rate throughout the measurement process. However, it is necessary to mimic an inhalation maneuver to disperse the powder into an aerosol when testing passive dry powder inhalers (DPIs), which constitute a significant portion of available products in this inhaler class. Methods in the pharmacopeial compendia intended for product quality assurance initiate sampling by applying a vacuum to the measurement apparatus using a timer-operated solenoid valve located downstream of the CI, resulting in a period when the flow rate through the impactor rapidly increases from zero towards the target flow rate. This article provides recommendations for achieving consistent APSD measurements, including selection of the CI, pre-separator, and flow control equipment, as well as reviewing considerations that relate to the shape of the flow rate-sampling time profile. Evidence from comparisons of different DPIs delivering the same active pharmaceutical ingredients (APIs) is indicative that the compendial method for APSD measurement is insensitive as a predictor of pharmacokinetic outcomes. Although inappropriate for product quality testing, guidance is therefore provided towards adopting a more clinically realistic methodology, including the use of an anatomically appropriate inlet and mimicking patient inhalation at the DPI while operating the CI at constant flow rate. Many of these recommendations are applicable to the testing of other OIP classes.

Effect of USP Induction Ports, Glass Sampling Apparatus, and Inhaler Device Resistance on Aerodynamic Patterns of Fluticasone Propionate-Loaded Engineered Mannitol Microparticles

The present investigation is to study the effect of two different induction ports (IP), i.e., USP IP and USP-modified IP equipped with andersen cascade impactor on in vitro aerodynamic performance along with the impact of USP-modified glass sampling apparatus on delivered dose uniformity of fluticasone propionate (FP) dry powder inhaler (DPI). FP DPI was fabricated by spray drying technique using engineered mannitol microparticles (EMP) with different force controlling agents, i.e., leucine and magnesium stearate. Additionally, commercially available two DPI inhaler devices namely Handihaler® and Breezhaler® were used to aerosolize the FP blends. Spherical smooth surface of EMP showed good powder flow properties and acceptable percentage content uniformity (> 95%). Amounts of FP deposited in cascade assembly using USP-modified IP with the Breezhaler® device was significantly higher (1.32-fold) as compared with the Handihaler® device. Moreover, USP-modified IP showed better deposition as compared with USP IP. Additionally, both inhaler devices showed a satisfactory delivered dose (> 105%) for FP using modified glass sampling apparatus at a flow rate of 60 L/min for 2 s. It was interesting to note that not only formulation properties but also IP geometry and device resistance have significant impact on DPI deposition pattern. This study is a first detailed account of aerodynamic performance of FP using USP-modified IP and USP-modified glass sampling apparatus. Thus, it can be of potential importance for both the academic and industry perspective.

Measurement of Aerodynamic Particle Size Distribution of Orally Inhaled Products by Cascade Impactor: How to Let the Product Specification Drive the Quality Requirements of the Cascade Impactor

The multi-stage inertial cascade impactor is used to determine the mass-weighted aerodynamic particle size distribution (APSD) as a critical quality attribute for orally inhaled products (OIPs). These apparatuses progressively size-fractionate the aerosol passing through a series of stages containing one or more nozzles, by increasing particle velocity. Nozzle sizes for a given multi-nozzle stage can be described collectively by effective diameter ([Formula: see text]), related to the cut-point size, providing the link to aerodynamic diameter. Users undertake stage mensuration periodically to assure that each stage [Formula: see text] remains within the manufacturer's tolerance, but there is no guidance on how frequently such checks should be made. We examine the philosophy that particle size-related specifications of the OIP should determine when an impactor is mensurated. Taking an example of a dry powder inhaler-generated aerosol sampled via a Next Generation Impactor with pre-separator, we find that there are only three critical stages that could have a material effect on the measured APSD specified as four groupings of stages following current regulatory practice. Furthermore, [Formula: see text] for the most critical stage having the smallest nozzle sizes could be relaxed by a factor of four or more before risking an inability to measure the mass fraction of API in the group containing the finest particles to a specification within ± 10% of nominal. We therefore conclude that users should consider letting the specification for APSD performance of an OIP in terms of accepted stage groupings drive the impactor quality requirements and frequency that stage mensuration is undertaken.

CFPD simulation of magnetic drug delivery to a human lung using an SAW nebulizer

Targeted drug delivery is an impressive topic that attracted the attention of many scientists in various scientific communities. Magnetic drug targeting is one of the targeted drug delivery techniques, which uses the magnetic field to externally control the magnetic drug particles. In this study, we aim to assess the magnetic drug delivery to the human respiratory system using a new aerosolization technique driven by surface acoustic waves (SAWs) into a realistic lung model geometrically reconstructed using computed tomography scan images. To achieve this aim, a simulation study using computational fluid-particle dynamics considering the Lagrangian approach for particle tracking is carried out. An external magnetic field was applied to govern the Magnetit (Fe₃O₄) particles as the magnetic drug career. The drug particles were assumed to be spherical and inert. The effects of magnetic field intensity, magnetic source position, and SAW injection position were examined for a light breathing condition (Q = 15 L/min). Given the realistic geometry of the respiratory system and its complexity, the airflow patterns vary as it penetrates deeper into the lung and experiences many irregularities, and bending deflections exist in the airways model. High-inertia particles tend to deposit at locations where the geometry experiences a significant reduction in cross section. Our results show that the magnetic field highly affects the particle deposition efficiency for fourfold. However, the magnet and SAW injection positions have a low impact on the deposition efficiency of drug particles.

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.

Advances in experimental and mechanistic computational models to understand pulmonary exposure to inhaled drugs

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.

Experimental and computational study of the effect of breath-actuated mechanism built in the NEXThaler® dry powder inhaler

The breath-actuated mechanism (BAM) is a mechanical unit included in NEXThaler^® with the role of delaying the emission of the drug until the inhalation flow rate of the patient is sufficiently high to detach the drug particles from their carriers. The main objective of this work was to analyse the effect of the presence of BAM on the size distribution of the emitted drug and its airway deposition efficiency and distribution. Study of the hygroscopic growth of the emitted drug particles and its effect on the deposition was another goal of this study. Size distributions of Foster^® NEXThaler^® drug particles emitted by dry powder inhalers with and without BAM have been measured by a Next Generation Impactor. Three characteristic inhalation profiles of asthmatic patients (low, moderate and high flow rates) were used for both experimental and modelling purposes. Particle hygroscopic growth was determined by a new method, where experimental measurements are combined with simulations. Upper airway and lung deposition fractions were computed assuming 5s and 10s breath-hold times. By the inclusion of BAM the fine particle fraction of the steroid component increased from 24 to 30% to 47-51%, while that of bronchodilator from 25-34% to 52-55%. The predicted upper airway steroid and bronchodilator doses decreased from about 60% to 35-40% due to BAM. At the same time, predicted lung doses increased from about 20%-35% (steroid) and from 22% to 38% (bronchodilator) for the moderate flow profile and from about 25% to 40% (steroid) and from 29% to 47% (bronchodilator) for the high inhalation flow profile. Although BDP and FF upper airway doses decreased by a factor of about two when BAM was present, lung doses of both components were about the same in the BAM and no-BAM configurations at the weakest flow profile. However, lung dose increased by 2-3% even for this profile when hygroscopic growth was taken into account. In conclusion, the NEXThaler^® BAM mechanism is a unique feature enabling high emitted fine particle fraction and enhanced drug delivery to the lungs.

Application of a One-Dimensional Computational Model for the Prediction of Deposition from a Dry Powder Inhaler

BACKGROUND

Accurate prediction of the regional deposition of inhaled dry powders as a function of powder properties and breathing pattern is a long-term research goal for pulmonary drug delivery. In the present work, deposition along the respiratory tract of dry powders of Fluticasone propionate and Salmeterol is predicted.

METHODS

A one-dimensional particle transport and deposition model is used, whose novelty is in the treatment of the alveolar space of each airway generation as an efficient mixing chamber. This assumption has been supported by simulations and measurements during the last 20 years. The model is applied to two popular pulmonary tree geometries, to investigate the effect of particle size on localized deposition and to estimate the uncertainty due to variations in airway size.

RESULTS AND CONCLUSIONS

Application of the model for the specific particle size distribution measured by a cascade impactor in the marketed product ELPENhaler, predicts the whole lung deposition (WLD), as well as the split between pulmonary (PU) and tracheobronchial (TB) deposition. Introduction in the model of modified particle size distributions with increased fractions of fine particles, indicates that the fine-particle dose is a satisfactory predictor of WLD but not of the PU/TB ratio.

Real life dose emission characterization using COPD patient inhalation profiles when they inhaled using a fixed dose combination (FDC) of the medium strength Symbicort® Turbuhaler®

The dose emitted from dry powder inhalers (DPI) is inhalation flow dependent and so varies with the peak inhalation flow (PIF) of a patient's inhalation maneuver (IM). Dose emission could also be affected by other IM parameters-the inhaled volume (V_in) and the initial acceleration rate of the IM (ACIM). We have adapted the compendial method for in-vitro DPI determinations so that inhalation profiles replace the inhalation square profile generated by a vacuum pump. These real-life patient inhalation profiles were measured when 18 COPD patients inhaled through an empty placebo Symbicort^® Turbuhaler^®. They have been used to identify the dose emission characteristics from a fixed dosed combination of 200μg budesonide plus 6μg formoterol Turbuhaler^®. To isolate each inhalation parameter some profiles were modified to provide a further 9 profiles to study the influence of V_in and 27 to identify the effect of ACIM. The fine particle dose, total emitted dose and mass median aerodynamic diameter were significantly (p<0.05) influenced by PIF (p<0.05) whereas ACIM and V_in had only a small effect. The results show the value of this ex-vivo methodology to provide an insight into the dose that each patient would have inhaled during real-life use.

Dry powder inhalation: past, present and future

INTRODUCTION

Early dry powder inhalers (DPIs) were designed for low drug doses in asthma and COPD therapy. Nearly all concepts contained carrier-based formulations and lacked efficient dispersion principles. Therefore, particle engineering and powder processing are increasingly applied to achieve acceptable lung deposition with these poorly designed inhalers. Areas covered: The consequences of the choices made for early DPI development with respect of efficacy, production costs and safety and the tremendous amount of energy put into understanding and controlling the dispersion performance of adhesive mixtures are discussed. Also newly developed particle manufacturing and powder formulation processes are presented as well as the challenges, objectives, and new tools available for future DPI design. Expert opinion: Improved inhaler design is desired to make DPIs for future applications cost-effective and safe. With an increasing interest in high dose drug delivery, vaccination and systemic delivery via the lungs, innovative formulation technologies alone may not be sufficient. Safety is served by increasing patient adherence to the therapy, minimizing the use of unnecessary excipients and designing simple and self-intuitive inhalers, which give good feedback to the patient about the inhalation maneuver. For some applications, like vaccination and delivery of hygroscopic formulations, disposable inhalers may be preferred.

Effects of ramp-up of inspired airflow on in vitro aerosol dose delivery performance for certain dry powder inhalers

This study investigated the effect of airflow ramp-up on the dose delivery performance of seven dry powder inhalers, covering a broad range of powder formulations and powder dispersion mechanisms. In vitro performance tests were performed at a target pressure drop of 4kPa, using two inspiratory flow ramp-up conditions, representing slow and fast ramp-up of airflow, respectively. The fluidization of bulk powder and aerosol clearance from the inhaler was assessed by laser photometer evaluation of aerosol emission kinetics and measurement of the delivered dose (DD). The quality of aerosol dispersion (i.e. de-agglomeration) and associated lung targeting performance was assessed by measuring the total lung dose (TLD) using the Alberta idealized mouth-throat model. The ratio of DD and TLD under slow/fast ramp conditions was used as a metric to rank-order flow ramp effects. Test results show that the delivered dose is relatively unaffected by flow ramp (DD ratio ~1 for all dry powder inhalers). In contrast, the total lung dose showed significantly more variation as a function of flow ramp and inhaler type. Engineered (spray dried) powder formulations were associated with relatively high TLD (>50% of nominal dose) compared to lactose blend and agglomerate based formulations, which had a lower TLD (7-40% of nominal dose), indicative of less efficient targeting of the lung. The TLD for the Tobi Podhaler was the least influenced by flow ramp (TLD ratio ~1), while the TLD for the Asmanex Twisthaler was the most sensitive to flow ramp (TLD ratio ≪1). The relatively high sensitivity of the Asmanex Twisthaler to flow ramp is attributed to rapid aerosol clearance (from the inhaler) combined with a strong effect of flow-rate on particle de-agglomeration and resulting size distribution.

De-agglomeration Effect of the US Pharmacopeia and Alberta Throats on Carrier-Based Powders in Commercial Inhalation Products

The US pharmacopeia (USP) and Alberta throats were recently reported to cause further de-agglomeration of carrier-free powders emitted from some dry powder inhalers (DPIs). This study assessed if they have similar influences on commercially available carrier-based DPIs. A straight tube, a USP throat, and an Alberta throat (non-coated and coated) were used for cascade impaction testing. Aerosol fine particle fraction (FPF ≤ 5 μm) was computed to evaluate throat-induced de-agglomeration. Computational fluid dynamics are employed to simulate airflow patterns and particle trajectories inside the USP and Alberta throats. For all tested products, no significant differences in the in vitro aerosol performance were observed between the USP throat and the straight tube. Using fine lactose carriers (<10 μm), Symbicort(®) and Oxis(™) showed minimal impaction inside the Alberta throat and resulted in similar FPF among all induction ports. For products using coarse lactose carriers (>10 μm), impaction frequency and energy inside the Alberta throat were significant. Further de-agglomeration was noted inside the non-coated Alberta throat for Seretide(®) and Spiriva(®), but agglomerates emitted from Relenza(®), Ventolin(®), and Foradil(®) did not further break up into smaller fractions. The coated Alberta throat considerably reduced the FPF values of these products due to the high throat retention, but they generally agreed better with the in vivo data. In conclusion, depending on the powder formulation (including carrier particle size), the inhaler, and the induction port, further de-agglomeration could happen ex-inhaler and create differences in the in vitro measurements.

Mechanisms of pharmaceutical aerosol deposition in the respiratory tract

Aerosol delivery is noninvasive and is effective in much lower doses than required for oral administration. Currently, there are several types of therapeutic aerosol delivery systems, including the pressurized metered-dose inhaler, the dry powder inhaler, the medical nebulizer, the solution mist inhaler, and the nasal sprays. Both oral and nasal inhalation routes are used for the delivery of therapeutic aerosols. Following inhalation therapy, only a fraction of the dose reaches the expected target area. Knowledge of the amount of drug actually deposited is essential in designing the delivery system or devices to optimize the delivery efficiency to the targeted region of the respiratory tract. Aerosol deposition mechanisms in the human respiratory tract have been well studied. Prediction of pharmaceutical aerosol deposition using established lung deposition models has limited success primarily because they underestimated oropharyngeal deposition. Recent studies of oropharyngeal deposition of several drug delivery systems identify other factors associated with the delivery system that dominates the transport and deposition of the oropharyngeal region. Computational fluid dynamic simulation of the aerosol transport and deposition in the respiratory tract has provided important insight into these processes. Investigation of nasal spray deposition mechanisms is also discussed.