Development of an effective two-equation turbulence modeling approach for simulating aerosol deposition across a range of turbulence levels.

Pharmaceutical aerosol systems present a significant challenge to computational fluid dynamics (CFD) modeling based on the need to capture multiple levels of turbulence, frequent transition between laminar and turbulent flows, anisotropic turbulent particle dispersion, and near-wall particle transport phenomena often within geometrically complex systems over multiple time scales. Two-equation turbulence models, such as the k-ω family of approximations, offer a computationally efficient solution approach, but are known to require the use of near-wall (NW) corrections and eddy interaction model (EIM) modifications for accurate predictions of aerosol deposition. The objective of this study was to develop an efficient and effective two-equation turbulence modeling approach that enables accurate predictions of pharmaceutical aerosol deposition across a range of turbulence levels. Key systems considered were the traditional aerosol deposition benchmark cases of a 90-degree bend (Re=6,000) and a vertical straight section of pipe (Re=10,000), as well as a highly complex case of direct-to-infant (D2I) nose-to-lung pharmaceutical aerosol delivery from an air-jet dry powder inhaler (DPI) including a patient interface and infant nasal geometry through mid-trachea (500

New Air-Jet Dry Powder Insufflator for High-Efficiency Aerosol Delivery to Rats.

Pulmonary deposition of lung-targeted therapeutic aerosols can achieve direct drug delivery to the site of action, thereby enhancing the efficacy and reducing systemic exposure. In this study, we investigated the in vitro and in vivo aerosol performance of the novel small animal air-jet dry powder insufflator (Rat AJ DPI) using spray-dried albuterol excipient-enhanced-growth (EEG) powder as a model formulation. The in vitro aerosolization performance of the optimized albuterol EEG powder was first assessed using the Rat AJ DPI. The performance of Rat AJ DPI to deliver albuterol EEG aerosol to rat lungs was then compared to that of the Penn-Century Insufflator. Albuterol EEG powders dispersed using the Rat AJ DPI demonstrated narrow unimodal aerosol size distribution profiles, which were independent of the loaded powder dose (1, 2, and 5 mg). In addition, the span value for Rat AJ DPI (5 mg powder mass) was 1.32, which was 4.2-fold lower than that for Penn-Century insufflator (5 mg powder mass). At a higher loaded mass of 5 mg, the Rat AJ DPI delivered significantly larger doses to rat lungs compared with the Penn-Century DPI. The Rat AJ DPI with hand actuation delivered approximately 85% of the total emitted dose (2 and 5 mg loadings), which was comparatively higher than that for Penn-Century DPI (approximately 75%). In addition, percentage deposition in each of the lung lobes for the Rat AJ DPI was observed to be independent of the administration dose (2 and 5 mg loadings) with coefficients of variation below 12%, except in the right middle lobe. Automatic actuation of a 5 mg powder mass using the Rat AJ DPI demonstrated a similar delivered dose compared to manual actuation of the same dose, with 82% of the total emitted dose reaching the lung lobes. High-efficiency delivery of the aerosol to the lobar lung region and low sensitivity of the interlobar delivery efficiency to the loaded dose highlight the suitability of the new air-jet DPI for administering therapeutic pharmaceutical aerosols to small test animals.

Near Elimination of In Vitro Predicted Extrathoracic Aerosol Deposition in Children Using a Spray-Dried Antibiotic Formulation and Pediatric Air-Jet DPI.

PURPOSE: This study evaluated the in vitro aerosol performance of a dry powder antibiotic product that combined a highly dispersible tobramycin powder with a previously optimized pediatric air-jet dry powder inhaler (DPI) across a subject age range of 2-10 years. METHODS: An excipient enhanced growth (EEG) formulation of the antibiotic tobramycin (Tobi) was prepared using a small particle spray drying technique that included mannitol as the hygroscopic excipient and trileucine as the dispersion enhancer. The Tobi-EEG formulation was aerosolized using a positive-pressure pediatric air-jet DPI that included a 3D rod array. Realistic in vitro experiments were conducted in representative airway models consistent with children in the age ranges of 2-3, 5-6 and 9-10 years using oral or nose-to-lung administration, non-humidified or humidified airway conditions, and constant or age-specific air volumes. RESULTS: Across all conditions tested, mouth-throat depositional loss was < 1% and nose-throat depositional loss was < 3% of loaded dose. Lung delivery efficiency was in the range of 77.3-85.1% of loaded dose with minor variations based on subject age (~ 8% absolute difference), oral or nasal administration (< 2%), and delivered air volume (< 2%). Humidified airway conditions had an insignificant impact on extrathoracic depositional loss and significantly increased aerosol size at the exit of a representative lung chamber. CONCLUSIONS: In conclusion, the inhaled antibiotic product nearly eliminated extrathoracic depositional loss, demonstrated high efficiency nose-to-lung antibiotic aerosol delivery in pediatric airway models for the first time, and provided ~ 80% lung delivery efficiency with little variability across subject age and administered air volume.

Computational Fluid Dynamics (CFD) Guided Spray Drying Recommendations for Improved Aerosol Performance of a Small-Particle Antibiotic Formulation.

PURPOSE: The objective of this study was to implement computational fluid dynamics (CFD) simulations and aerosol characterization experiments to determine best-case spray drying conditions of a tobramycin excipient enhanced growth (Tobi-EEG) formulation for use in a pediatric air-jet dry powder inhaler (DPI). METHODS: An iterative approach was implemented in which sets of spray drying conditions were explored using CFD simulations followed by lead candidate selection, powder production and in vitro aerosol testing. CFD simulations of a small-particle spray dryer were performed to capture droplet drying parameters and surface-averaged temperature and relative humidity (RH) conditions in the powder collection region. In vitro aerosol testing was performed for the selected powders using the pediatric air-jet DPI, cascade impaction, and aerosol transport through a pediatric mouth-throat (MT) model to a tracheal filter. RESULTS: Based on comparisons of CFD simulations and in vitro powder performance, recommended drying conditions for small-particle powders with electrostatic collection include: (i) reducing the CFD-predicted drying parameters of κavg and κmax to values below 3 µm2/ms and 114 µm2/ms, respectively; (ii) maintaining the Collector Surface RH within an elevated range, which for the Tobi-EEG formulation with l-leucine was 20-30 %RH; and (iii) ensuring that particles reaching the collector were fully dried, based on a mass fraction of solute CFD parameter. CONCLUSIONS: Based on the newly recommended spray dryer conditions for small particle aerosols, delivery performance of the lead Tobi-EEG formulation was improved resulting in >60% of the DPI loaded dose passing through the pediatric MT model.

Development of a High-Dose Infant Air-Jet Dry Powder Inhaler (DPI) with Passive Cyclic Loading of the Formulation.

PURPOSE: The objective of this study was to incorporate a passive cyclic loading strategy into the infant air-jet dry powder inhaler (DPI) in a manner that provides high efficiency aerosol lung delivery and is insensitive to powder mass loadings and the presence of downstream pulmonary mechanics. METHODS: Four unique air-jet DPIs were initially compared and the best performing passive design (PD) was selected for sensitivity analyses. A single preterm in vitro nose-throat (NT) model, air source, and nasal interface were utilized throughout. While the majority of analyses were evaluated with a model spray-dried excipient enhanced growth (EEG) formulation, performance of a Surfactant-EEG formulation was also explored for the lead DPI design. RESULTS: Two devices, PD-2 and PD-3, evaluated in the preterm model achieved an estimated lung delivery efficiency of 60% with the model EEG formulation, and were not sensitive to the loaded dose (10-30 mg of powder). The PD-3 device was also unaffected by the presence of downstream pulmonary mechanics (infant lung model) and had only a minor sensitivity to tripling the volume of the powder reservoir. When using the Surfactant-EEG formulation, increasing the actuation flow rate from 1.7 to 4.0 L/min improved lung delivery by nearly 10%. CONCLUSIONS: The infant air-jet DPI platform was successfully modified with a passive cyclic loading strategy and capable of providing an estimated > 60% lung delivery efficiency of a model spray-dried formulation with negligible sensitivity to powder mass loading in the range of 10-30 mg and could be scaled to deliver much higher doses.

In Vitro Evaluation of Nebulized Pharmaceutical Aerosol Delivery to the Lungs Using a New Heated Dryer System (HDS).

The objective of this study was to develop a new heated dryer system (HDS) for high efficiency lung delivery of nebulized aerosol and demonstrate performance with realistic in vitro testing for trans-nasal aerosol administration simultaneously with high-flow nasal cannula (HFNC) therapy and separately for direct oral inhalation (OI) of the aerosol. With the HDS-HFNC and HDS-OI platforms, new active synchronization control routines were developed to sense subject inhalation and coordinate drug aerosol delivery. In vitro experiments were conducted to predict regional drug loss and lung delivery efficiency in systems that included the HDS with various patient interfaces, realistic airway models, and simulated breathing waveforms. For the HDS-HFNC platform and a repeating breathing waveform, total system loss was < 10%, extrathoracic deposition was approximately 6%, and best-case lung delivery efficiency was 75-78% of nebulized dose. Inclusion of randomized breathing with the HFNC system decreased lung delivery efficiency by ~ 10% and had no impact on nasal depositional loss. For the HDS-OI platform and best-case mouthpiece, total system loss was < 8%, extrathoracic deposition was < 1%, and lung delivery efficiency was > 90% of nebulized dose. Normal vs. deep randomized oral inhalation had little impact on performance of the HDS-OI platform and environmental aerosol loss was negligible. In conclusion, both platforms demonstrated the potential for high efficiency lung delivery of the aerosol with the HDS-OI platform having the added advantages of nearly eliminating extrathoracic deposition, being insensitive to breathing waveform, and preventing environmental aerosol loss.

Characterizing the Effects of Nasal Prong Interfaces on Aerosol Deposition in a Preterm Infant Nasal Model.

The objective of this study was to characterize the effects of multiple nasal prong interface configurations on nasal depositional loss of pharmaceutical aerosols in a preterm infant nose-throat (NT) airway model. Benchmark in vitro experiments were performed in which a spray-dried powder formulation was delivered to a new preterm NT model with a positive-pressure infant air-jet dry powder inhaler using single- and dual-prong interfaces. These results were used to develop and validate a computational fluid dynamics (CFD) model of aerosol transport and deposition in the NT geometry. The validated CFD model was then used to explore the NT depositional characteristic of multiple prong types and configurations. The CFD model highlighted a turbulent jet effect emanating from the prong(s). Analysis of NT aerosol deposition efficiency curves for a characteristic particle size and delivery flowrate (3 µm and 1.4 L/min (LPM)) revealed little difference in NT aerosol deposition fraction (DF) across the prong insertion depths of 2-5 mm (DF = 16-24%) with the exception of a single prong with 5-mm insertion (DF = 36%). Dual prongs provided a modest reduction in deposition vs. a single aerosol delivery prong at the same flow for insertion depths < 5 mm. The presence of the prongs increased nasal depositional loss by absolute differences in the range of 20-70% compared with existing correlations for ambient aerosols. In conclusion, the use of nasal prongs was shown to have a significant impact on infant NT aerosol depositional loss prompting the need for prong design alterations to improve lung delivery efficiency.

Advancement of the Infant Air-Jet Dry Powder Inhaler (DPI): Evaluation of Different Positive-Pressure Air Sources and Flow Rates.

PURPOSE: In order to improve the delivery of dry powder aerosol formulations to the lungs of infants, this study implemented an infant air-jet platform and explored the effects of different air sources, flow rates, and pulmonary mechanics on aerosolization performance and aerosol delivery through a preterm nose-throat (NT) in vitro model. METHODS: The infant air-jet platform was actuated with a positive-pressure air source that delivered the aerosol and provided a full inhalation breath. Three different air sources were developed to provide highly controllable positive-pressure air actuations (using actuation volumes of ~10 mL for the preterm model). While providing different flow waveform shapes, the three air sources were calibrated to produce the same flow rate magnitude (Q90: 90th percentile of flow rate). Multiple air-jet DPI designs were coupled with the air sources and evaluated with a model spray-dried excipient enhanced growth formulation. RESULTS: Compared to other designs, the D1-Single air-jet DPI provided improved performance with low variability across all three air sources. With the tested D1-Single air-jet and Timer air source, reducing the flow rate from 4 to 1.7 L/min marginally decreased the aerosol size and significantly increased the lung delivery efficiency above 50% of the loaded dose. These results were not impacted by the presence of downstream pulmonary mechanics (resistance and compliance model). CONCLUSIONS: The selected design was capable of providing an estimated >50% lung delivery efficiency of a model spray-dried formulation and was not influenced by the air source, thereby enabling greater flexibility for platform deployment in different environments.

High-Efficiency Dry Powder Aerosol Delivery to Children: Review and Application of New Technologies.

While dry powder aerosol formulations offer a number of advantages, their use in children is often limited due to poor lung delivery efficiency and difficulties with consistent dry powder inhaler (DPI) usage. Both of these challenges can be attributed to the typical use of adult devices in pediatric subjects and a lack of pediatric-specific DPI development. In contrast, a number of technologies have recently been developed or progressed that can substantially improve the efficiency and reproducibility of DPI use in children including: (i) nose-to-lung administration with small particles, (ii) active positive-pressure devices, (iii) structures to reduce turbulence and jet momentum, and (iv) highly dispersible excipient enhanced growth particle formulations. In this study, these technologies and their recent development are first reviewed in depth. A case study is then considered in which these technologies are simultaneously applied in order to enable the nose-to-lung administration of dry powder aerosol to children with cystic fibrosis (CF). Using a combination of computational fluid dynamics (CFD) analysis and realistic in vitro experiments, device performance, aerosol size increases and lung delivery efficiency are considered for pediatric-CF subjects in the age ranges of 2-3, 5-6 and 9-10 years old. Results indicate that a new 3D rod array structure significantly improves performance of a nasal cannula reducing interface loss by a factor of 1.5-fold and produces a device emitted mass median aerodynamic diameter (MMAD) of 1.67 µm. For all ages considered, approximately 70% of the loaded dose reaches the lower lung beyond the lobar bronchi. Moreover, significant and rapid size increase of the aerosol is observed beyond the larynx and illustrates the potential for targeting lower airway deposition. In conclusion, concurrent CFD and realistic in vitro analysis indicates that a combination of multiple new technologies can be implemented to overcome obstacles that currently limit the use of DPIs in children as young as two years of age.

Performance of Low Air Volume Dry Powder Inhalers (LV-DPI) when Aerosolizing Excipient Enhanced Growth (EEG) Surfactant Powder Formulations.

Efficient delivery of dry powder aerosols dispersed with low volumes of air is challenging. This study aims to develop an efficient dry powder inhaler (DPI) capable of delivering spray-dried Survanta-EEG powders (3-10 mg) with a low volume (3 mL) of dispersion air. A series of iterative design modifications were made to a base low air volume actuated DPI. The modifications included the replacement of the original capsule chamber with an integral dose containment chamber, alteration of the entrainment air flow path through the device (from single-sided (SS) to straight through (ST)), change in the number of air inlet holes (from one to three), varying the outlet delivery tube length (45, 55, and 90 mm) and internal diameter (0.60, 0.89, and 1.17 mm). The modified devices were evaluated by determining the influence of the modifications and powder fill mass on aerosol performance of spray-dried Survanta-EEG powders. The optimal DPI was also evaluated for its ability to aerosolize a micronized powder. The optimized dose containment unit DPI had a 0.21 mL powder chamber, ST airflow path, three-0.60 mm air inlet holes, and 90 mm outlet delivery tube with 0.89 mm internal diameter. The powder dispersion characteristics of the optimal device were independent of fill mass with good powder emptying in one 3 mL actuation. At 10 mg fill mass, this device had an emitted mass of 5.3 mg with an aerosol Dv50 of 2.7 µm. After three 3 mL actuations, >85% of the spray-dried powder was emitted from the device. The emitted mass of the optimal device with micronized albuterol sulfate was >72% of the nominal fill mass of 10 mg in one 3 mL actuation. Design optimization produced a DPI capable of efficient performance with a dispersion air volume of 3 mL to aerosolize Survanta-EEG powders.

Development and Characterization of Excipient Enhanced Growth (EEG) Surfactant Powder Formulations for Treating Neonatal Respiratory Distress Syndrome.

This study aimed to develop and characterize a spray-dried powder aerosol formulation of a commercially available surfactant formulation, Survanta® intratracheal suspension, using the excipient enhanced growth (EEG) approach. Survanta EEG powders were prepared by spray drying of the feed dispersions containing Survanta® (beractant) intratracheal suspension, hygroscopic excipients (mannitol and sodium chloride), and a dispersion enhancer (l-leucine or trileucine) in 5 or 20% v/v ethanol in water using the Buchi Nano Spray Dryer B-90 HP. Powders were characterized for primary particle size, morphology, phospholipid content, moisture content, thermal properties, moisture sorption, and surface activity. The aerosol performance of the powders was assessed using a novel low-volume dry powder inhaler (LV-DPI) device operated with 3-mL volume of dispersion air. At both ethanol concentrations, in comparison to trileucine, l-leucine significantly reduced the primary particle size and span and increased the fraction of submicrometer particles of the Survanta EEG powders. The l-leucine-containing Survanta EEG powders exhibited good aerosolization performance with ≥ 88% of the mass emitted (% nominal) after 3 actuations from the modified LV-DPI device. In addition, l-leucine-containing powders had a low moisture content (< 3% w/w) with transition temperatures close to the commercial surfactant formulation and retained their surface tension reducing activity after formulation processing. A Survanta EEG powder containing l-leucine was developed which showed efficient aerosol delivery from the modified LV-DPI device using a low dispersion air volume.

Computational Fluid Dynamics (CFD) Simulations of Spray Drying: Linking Drying Parameters with Experimental Aerosolization Performance.

PURPOSE: The purpose of this study was to develop a new computational fluid dynamics (CFD)-based model of the complex transport and droplet drying kinetics within a laboratory-scale spray dryer, and relate CFD-predicted drying parameters to powder aerosolization metrics from a reference dry powder inhaler (DPI). METHODS: A CFD model of the Buchi Nano Spray Dryer B-90 was developed that captured spray dryer conditions from a previous experimental study producing excipient enhanced growth powders with L-leucine as a dispersion enhancer. The CFD model accounted for two-way heat and mass transfer coupling between the phases and turbulent flow created by acoustic streaming from the mesh nebulizer. CFD-based drying parameters were averaged across all droplets in each spray dryer case and included droplet time-averaged drying rate (κavg), maximum instantaneous drying rate (κmax) and precipitation window. RESULTS: CFD results highlighted a chaotic drying environment in which time-averaged droplet drying rates (κavg) for each spray dryer case had high variability with coefficients of variation in the range of 60-70%. Maximum instantaneous droplet drying rates (κmax) were discovered that were two orders of magnitude above time-averaged drying rates. Comparing CFD-predicted drying parameters with experimentally determined mass median aerodynamic diameters (MMAD) and emitted doses (ED) from a reference DPI produced strong linear correlations with coefficients of determination as high as R2 = 0.98. CONCLUSIONS: For the spray dryer system and conditions considered, reducing the CFD-predicted maximum drying rate experienced by droplets improved the aerosolization performance (both MMAD and ED) when the powders were aerosolized with a reference DPI.

Advancement of a Positive-Pressure Dry Powder Inhaler for Children: Use of a Vertical Aerosolization Chamber and Three-Dimensional Rod Array Interface.

PURPOSE: Available dry powder inhalers (DPIs) have very poor lung delivery efficiencies in children. The objective of this study was to advance and experimentally test a positive-pressure air-jet DPI for children based on the use of a vertical aerosolization chamber and new patient interfaces that contain a three-dimensional (3D) rod array structure. METHODS: Aerosolization performance of different air-jet DPI designs was first evaluated based on a 10 mg powder fill mass of a spray-dried excipient enhanced growth (EEG) formulation. Devices were actuated with positive pressure using flow rate (10-20 L/min) and inhaled volume (750 ml) conditions consistent with a 5-year-old child. Devices with best performance were connected to different mouthpiece designs to determine the effect on aerosolization and tested for aerosol penetration through a realistic pediatric in vitro mouth-throat model. RESULTS: Use of the new vertical aerosolization chamber resulted in high quality aerosol formation. Inclusion of a 3D rod array structure in the mouthpiece further reduced aerosol size by approximately 20% compared to conditions without a rod array, and effectively dissipated the turbulent jet leaving the device. Best case device and mouthpiece combinations produced < 2% mouth-throat depositional loss and > 70% lung delivery efficiency based on loaded dose. CONCLUSIONS: In conclusion, use of a 3D rod array in the MP of a positive-pressure air-jet DPI was found to reduce aerosol size by 20%, not significantly increase MP depositional loss, reduce mouth-throat deposition by 6.4-fold and enable lung delivery efficiency as high as 73.4% of loaded dose based on pediatric test conditions.

CFD Guided Optimization of Nose-to-Lung Aerosol Delivery in Adults: Effects of Inhalation Waveforms and Synchronized Aerosol Delivery.

PURPOSE: The objective of this study was to optimize nose-to-lung aerosol delivery in an adult upper airway model using computational fluid dynamics (CFD) simulations in order to guide subsequent human subject aerosol delivery experiments. METHODS: A CFD model was developed that included a new high-flow nasal cannula (HFNC) and pharmaceutical aerosol delivery unit, nasal cannula interface, and adult upper airway geometry. Aerosol deposition predictions in the system were validated with existing and new experimental results. The validated CFD model was then used to explore aerosol delivery parameters related to synchronizing aerosol generation with inhalation and inhalation flow rate. RESULTS: The low volume of the new HFNC unit minimized aerosol transit time (0.2 s) and aerosol bolus spread (0.1 s) enabling effective synchronization of aerosol generation with inhalation. For aerosol delivery correctly synchronized with inhalation, a small particle excipient-enhanced growth delivery strategy reduced nasal cannula and nasal depositional losses each by an order of magnitude and enabled ~80% of the nebulized dose to reach the lungs. Surprisingly, nasal deposition was not sensitive to inhalation flow rate due to use of a nasal cannula interface with co-flow inhaled air and the small initial particle size. CONCLUSIONS: The combination of correct aerosol synchronization and small particle size enabled high efficiency nose-to-lung aerosol delivery in adults, which was not sensitive to inhalation flow rate.

Dry powder aerosol containing muco-inert particles for excipient enhanced growth pulmonary drug delivery.

Tenacious sputum poses a critical diffusion barrier for aerosol antibiotics used to treat cystic fibrosis (CF) lung infection. We conducted a proof-of-concept study using dense poly(ethylene glycol) coated polystyrene nanoparticles (PS-PEG NPs) as model muco-inert particles (MIPs) formulated as a powder using an excipient enhanced growth (EEG) strategy, aiming to minimize extrathoracic airway loss, maximize deposition in the airway and further overcome the sputum barrier in the CF lungs. The EEG aerosol formulation containing PS-PEG MIPs was prepared by spray drying and produced discrete spherical particles with geometric diameter of approximately 2 µm; and >80% of the powder dose was delivered from a new small-animal dry powder inhaler (DPI). The MIPs released from the EEG aerosol had human airway mucus and CF sputum diffusion properties comparable to the suspension formulation. These properties make this formulation a promising pulmonary drug delivery system for CF lung infections.

Use of Computational Fluid Dynamics (CFD) Dispersion Parameters in the Development of a New DPI Actuated with Low Air Volumes.

PURPOSE: To determine the predictive power of computational fluid dynamics (CFD)-based dispersion parameters in the development of a new inline DPI that is actuated with low volumes of air. METHODS: Four new versions of a dose aerosolization and containment (DAC)-unit DPI were created with varying inlet and outlet orifice sizes and analyzed with results from five previous designs. A concurrent in vitro and CFD analysis was conducted to predict the emitted dose (ED; as a % of loaded dose) and aerosol mass median aerodynamic diameter (MMAD) produced by each device when actuated with 10 ml air bursts. CFD simulations of device operation were used to predict flow field and particle-based dispersion parameters. RESULTS: Comparisons of experimental and CFD results indicated that multiple flow field and particle-based dispersion parameters could be used to predict ED (minimum RMS Error = 4.9%) and MMAD (minimum RMS Error = 0.04 µm) to a high degree of accuracy. Based on experiments, the best overall device produced mean (standard deviation; SD) ED = 82.9(4.3)% and mean MMAD (SD) = 1.73(0.07)µm, which were in close agreement with the CFD predictions. CONCLUSIONS: A unique relationship was identified in the DAC-unit DPI in which reducing turbulence also reduced the MMAD.

Efficient Nose-to-Lung Aerosol Delivery with an Inline DPI Requiring Low Actuation Air Volume.

PURPOSE: To demonstrate efficient aerosol delivery through an in vitro nasal model using a dry powder inhaler (DPI) requiring low actuation air volumes (LV) applied during low-flow nasal cannula (LFNC) therapy. METHODS: A previously developed LV-DPI was connected to a LFNC system with 4 mm diameter tubing. System connections and the nasal cannula interface were replaced with streamlined components. To simulate nasal respiration, an in vitro nasal model was connected to a downstream lung simulator that produced either passive or deep nasal respiration. Performance of a commercial mesh nebulizer system was also considered. RESULTS: For the optimized system, steady state cannula emitted dose was 75% of the capsule loaded dose. With cyclic nasal breathing, delivery efficiency to the tracheal filter was 53-55% of the loaded dose, which was just under the design target of 60%. Compared with a commercially available mesh nebulizer, the optimal LV-DPI was 40-fold more efficient and 150 times faster in terms of delivering aerosol to the lungs. CONCLUSIONS: The optimized LV-DPI system is capable of high efficiency lung delivery of powder aerosols through a challenging nasal cannula interface.

Small Airway Absorption and Microdosimetry of Inhaled Corticosteroid Particles after Deposition.

PURPOSE: To predict the cellular-level epithelial absorbed dose from deposited inhaled corticosteroid (ICS) particles in a model of an expanding and contracting small airway segment for different particle forms. METHODS: A computational fluid dynamics (CFD)-based model of drug dissolution, absorption and clearance occurring in the surface liquid of a representative small airway generation (G13) was developed and used to evaluate epithelial dose for the same deposited drug mass of conventional microparticles, nanoaggregates and a true nanoaerosol. The ICS medications considered were budesonide (BD) and fluticasone propionate (FP). Within G13, total epithelial absorption efficiency (AE) and dose uniformity (microdosimetry) were evaluated. RESULTS: Conventional microparticles resulted in very poor AE of FP (0.37%) and highly nonuniform epithelial absorption, such that <5% of cells received drug. Nanoaggregates improved AE of FP by a factor of 57-fold and improved dose delivery to reach approximately 40% of epithelial cells. True nanoaerosol resulted in near 100% AE for both drugs and more uniform drug delivery to all cells. CONCLUSIONS: Current ICS therapies are absorbed by respiratory epithelial cells in a highly nonuniform manner that may partially explain poor clinical performance in the small airways. Both nanoaggregates and nanoaerosols can significantly improve ICS absorption efficiency and uniformity.

In Vitro Assessment of Small Charged Pharmaceutical Aerosols in a Model of a Ventilated Neonate.

Aerosolized medications may benefit infants receiving mechanical ventilation; however, the lung delivery efficiency of these aerosols is unacceptably low. In vitro experiments were conducted to evaluate aerosol delivery through conventional and modified ventilation systems to the end of a 3mm endotracheal tube (ETT) under steady state and realistic cyclic flow conditions. System modifications were employed to investigate the use of small charged particles and included streamlined components, a reduction in nebulizer liquid flow rate, synchronization with inspiration, and implementation of a previously designed low-flow induction charger (LF-IC), which was further modified in this study. Cyclic flow experiments implemented a modern ventilator with bias airflow and an inline flow meter, both of which are frequently excluded from in vitro tests but included in clinical practice. The modified LF-IC system demonstrated superior delivery efficiency to the end of the ETT (34%) compared with the commercial system (~1.3%) operating under cyclic ventilation conditions. These findings indicate that commercial systems still provide very low lung delivery efficiencies despite decades of innovation. In contrast, the modified system increased dose delivery to the end of the ETT by 26-fold. Despite initial concerns, the charged aerosol could be efficiently delivered through the small diameter ETT and reach the lungs. Future studies will be required to determine if the applied particle charge can eliminate expected high exhalation aerosol loss and will require the development of a realistic lung model.

Absorption and Clearance of Pharmaceutical Aerosols in the Human Nose: Effects of Nasal Spray Suspension Particle Size and Properties.

PURPOSE: The objective of this study was to use a recently developed nasal dissolution, absorption, and clearance (DAC) model to evaluate the extent to which suspended drug particle size influences nasal epithelial drug absorption for a spray product. METHODS: Computational fluid dynamics (CFD) simulations of mucociliary clearance and drug dissolution were used to calculate total and microscale epithelial absorption of drug delivered with a nasal spray pump. Ranges of suspended particle sizes, drug solubilities, and partition coefficients were evaluated. RESULTS: Considering mometasone furoate as an example, suspended drug particle sizes in the range of 1-5 µm did not affect the total nasal epithelial uptake. However, the microscale absorption of suspended drug particles with low solubilities was affected by particle size and this controlled the extent to which the drug penetrated into the distal nasal regions. CONCLUSIONS: The nasal-DAC model was demonstrated to be a useful tool in determining the nasal exposure of spray formulations with different drug particle sizes and solubilities. Furthermore, the model illustrated a new strategy for topical nasal drug delivery in which drug particle size is selected to increase the region of epithelial surface exposure using mucociliary clearance while minimizing the drug dose exiting the nasopharynx.