Louis S. and Ruth S. Harris Exceptional Scholar Professor, Department of Mechanical and Nuclear Engineering
Engineering East Hall, Room E3248, Richmond, VA, UNITED STATES
Professor Longest works to address significant current challenges in the field of medical aerosols
Journal of Aerosol Science2019-03-07
Journal of Aerosol Medicine and Pulmonary Drug Delivery2018-06-01
2007 - 2010
2000 - 2001
1998 - 1999
Ph.D., Mechanical Engineering
M.S., Mechanical Engineering
B.S., Mechanical Engineering
Journal of aerosol medicine and pulmonary drug delivery 34 (1), 57-70
C Howe, M Hindle, S Bonasera, V Rani, PW Longest
Background: Positive-pressure dry powder inhalers (DPIs) have recently been developed that in combination with highly dispersible spray-dried powder formulations can achieve high efficiency aerosolization with low actuation air-volumes (AAVs). The objective of this study was to initially develop the positive-pressure air-jet DPI platform for high efficiency aerosol delivery to newborn infants by using the nose-to-lung route.
Methods: Aerosolization performance metrics of six air-jet DPIs were first assessed at AAVs that were consistent with full-term (30 mL) and preterm (10 mL) neonates. Designs of the air-jet DPIs varied based on geometry of the inlet and outlet flow passages and shape of the aerosolization chamber. Aerosolization metrics evaluated at the device outlet were emitted dose (ED) and mass median aerodynamic diameter (MMAD). Designs with the best aerosolization performance were connected to a smoothly expanding nasal interface and full-term infant (3550 g) nose-throat (NT) model with tracheal filter.
Results: The three best performing devices had characteristics of a cylindrical and horizontal aerosolization chamber with a flush or protruding outlet orifice. Including multiple air inlets resulted in meeting the aerosolization targets of >80% ED (based on loaded dose) and MMAD
International Journal of Pharmaceutics 591, 120027
A Hassan, D Farkas, W Longest, M Hindle
Spray drying can be utilized to produce highly dispersible powder aerosol formulations. However, these formulations are known to be hygroscopic, leading to potential solid-state stability and aerosol performance issues. This study aims to investigate if control of the spray drying particle formation conditions could be employed to improve the solid-state stability and alter the aerosol performance of tobramycin EEG formulations. Eight formulations were prepared, each had the same drug:excipient ratio of 60%w/w tobramycin, 20% w/w l-leucine, 18% w/w mannitol, and 2% w/w poloxamer 188. An experimental design matrix was performed with drying air water content of 1 or 10 g/m3 and spray drying solution l-leucine concentrations of 4.6, 7.6, 15.2 or 23.0 mmol/L. The particle size, morphology and crystallinity of spray dried formulations were characterized together with their dynamic moisture vapor sorption and aerosol performance. Higher crystallization and glass transition %RH were observed for the formulations spray dried using drying air with higher water content indicating more stable characteristics. Initial screening using a handheld dry powder inhaler of the realistic aerosol performance revealed that neither changing l-leucine concentration nor the drying gas water content affect the in-vitro expected lung dose. However, using a novel positive pressure inhaler, formulations produced using spray drying solutions with lower l-leucine concentrations showed better aerosol performance with MMAD around 2 µm and FPF < 5 µm around 80%.view more
Journal of aerosol medicine and pulmonary drug delivery 33 (6), 314-322
Franck J Kamga Gninzeko, Michael S Valentine, Cindy K Tho, Sahil R Chindal, Susan Boc, Sneha Dhapare, Mohammad Abdul Motalib Momin, Amr Hassan, Michael Hindle, Dale R Farkas, P Worth Longest, Rebecca L Heise
Background: In neonatal respiratory distress syndrome, breathing support and surfactant therapy are commonly used to enable the alveoli to expand. Surfactants are typically delivered through liquid instillation. However, liquid instillation does not specifically target the small airways. We have developed an excipient enhanced growth (EEG) powder aerosol formulation using Survanta®.
Methods: EEG Survanta powder aerosol was delivered using a novel dry powder inhaler via tracheal insufflation to surfactant depleted rats at nominal doses of 3, 5, 10, and 20 mg of powder containing 0.61, 0.97, 1.73, and 3.46 mg of phospholipids (PL), whereas liquid Survanta was delivered via syringe instillation at doses of 2 and 4 mL/kg containing 18.6 and 34 mg of PL. Ventilation mechanics were measured before and after depletion, and after treatment. We hypothesized that EEG Survanta powder aerosol would improve lung mechanics compared with instilled liquid Survanta in surfactant depleted rats.
Results and Conclusion: EEG Survanta powder aerosol at a dose of 0.61 mg PL significantly improved lung compliance and elastance compared with the liquid Survanta at a dose of 18.6 mg, which represents improved primary efficacy of the aerosol at a 30-fold lower dose of PL. There was no significant difference in white blood cell count of the lavage from the EEG Survanta group compared with liquid Survanta. These results provide an in vivo proof-of-concept for EEG Survanta powder aerosol as a promising method of surfactant replacement therapy.
Journal of Aerosol Science, 105692
K Bass, D Farkas, A Hassan, S Bonasera, M Hindle, W Longest
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.view more
Journal of Pharmaceutical Sciences
With the steadily increasing price of medications in the US market, the introduction of cost-effective generic products is typically viewed as favorable for consumers. For a generic pharmaceutical nasal spray suspension formulation to enter the marketplace, a demonstration of bioequivalence between an innovator and the generic product is required by the US Food and Drug Administration to ensure that the generic product has equivalent local delivery, equivalent systemic exposure, and equivalent in vitro performance, together ...
Journal of Aerosol Medicine and Pulmonary Drug Delivery
The objective of this study was to compare aerosol deposition predictions of a new whole-airway CFD model with available in vivo data for a dry powder inhaler (DPI) considered across multiple inhalation waveforms, which affect both the particle size distribution (PSD) and particle deposition...
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...
Journal of Aerosol Medicine and Pulmonary Drug Delivery
The amount of drug aerosol from an inhaler that can pass through an in vitro model of the mouth and throat (MT) during a realistic breath or inhalation flow rate vs. time profile (IP) is designated the total lung dose in vitro, or TLDin vitro. This article describes a clinical study that enabled us to recommend a general method of selecting IPs for use with powder inhalers of known airflow resistance (R) provided subjects followed written instructions either alone or in combination with formal training...
Journal of Pharmaceutical Sciences
To evaluate the regional delivery of conventional aerosol medications, a new whole-lung computational fluid dynamics modeling approach was applied for metered dose inhaler (MDI) and dry powder inhaler (DPI) aerosols delivered to healthy and constricted airways. The computational fluid dynamics approach included complete airways through the third respiratory bifurcation (B3) and applied the new stochastic individual pathway modeling technique beyond B3 through the remainder of the conducting airways together with a ...