National and international guidelines recommend droplet/airborne transmission and contact precautions for those caring for coronavirus disease 2019 (COVID-19) patients in ambulatory and acute care settings. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus, an acute respiratory infectious agent, is primarily transmitted between people through respiratory droplets and contact routes. A recognized key to transmission of COVID-19, and droplet infections generally, is the dispersion of bioaerosols from the patient. Increased risk of transmission has been associated with aerosol generating procedures that include endotracheal intubation, bronchoscopy, open suctioning, administration of nebulized treatment, manual ventilation before intubation, turning the patient to the prone position, disconnecting the patient from the ventilator, noninvasive positive-pressure ventilation, tracheostomy, and cardiopulmonary resuscitation. The knowledge that COVID-19 subjects can be asymptomatic and still shed virus, producing infectious droplets during breathing, suggests that health care workers (HCWs) should assume every patient is potentially infectious during this pandemic. Taking actions to reduce risk of transmission to HCWs is, therefore, a vital consideration for safe delivery of all medical aerosols. Guidelines for use of personal protective equipment (glove, gowns, masks, shield, and/or powered air purifying respiratory) during high-risk procedures are essential and should be considered for use with lower risk procedures such as administration of uncontaminated medical aerosols. Bioaerosols generated by infected patients are a major source of transmission for SARS CoV-2, and other infectious agents. In contrast, therapeutic aerosols do not add to the risk of disease transmission unless contaminated by patients or HCWs.

The Biopharmaceutics Classification System (BCS), developed in the 1990s for oral immediate release drugs, is utilized by R&D scientists and regulators to streamline product development and regulatory approval timelines. This elegant, science-based approach is based on three in vitro parameters representing a combination of drug substance physicochemical and physiological properties with respect to oral administration; specifically a dose number, dissolution number, and absorption number. Interest in applying similar principles to pulmonary drug products is increasing. To date the focus has been on dissolution of drugs in the lung. A workshop co-sponsored by the AAPS, FDA, and USP was held in March 2015 in Baltimore to evaluate if a systematic framework to classify pulmonary drugs could be established, and the scope and relevance of such a classification scheme. The focus of the workshop was to address factors influencing drug delivery and action in the lungs rather than the development of a specific model or system. Presentations included: the history and evolution of the oral BCS (described as the "giBCS" by Gordon Amidon), lung physiology and the fate of inhaled drugs, regional aerosol deposition and dose, macroscopic clearance mechanisms, particle dissolution, drug permeability, absorption and their interplay with pharmacokinetics and pharmacodynamics. Background discussions were followed by three separate breakout sessions each focused on the BCS concepts of dose, dissolution, and absorption numbers as they would apply to pulmonary drug delivery. The workshop concluded that a classification system, if fully developed, would be a useful tool for formulators and discovery chemists. The scope of such a system, at this point in time, would not include aspects relevant to regulatory relief. The goals of the workshop were met by identifying an opportunity to develop a model to classify pulmonary drugs based on physicochemical attributes specific to lung physiology and drug delivery.

Two-dimensional (2D or planar) imaging with (99m)Tc radiolabels enables quantification of whole-lung and regional lung depositions for orally inhaled drug products. This article recommends standardized methodology for 2D imaging studies. Simultaneous anterior and posterior imaging with a dual-headed gamma camera is preferred, but imaging with a single-headed gamma camera is also acceptable. Correction of raw data for the effects of gamma ray attenuation is considered essential for accurate quantification, for instance, using transmission scanning with a flood-field source of (99m)Tc or (57)Co. Evidence should be provided of the accuracy of the quantification method, for instance, by determining "mass balance." Lung deposition may be expressed as a percentage of ex-valve or ex-device dose, but should also be given as mass of drug when possible. Assessment of regional lung deposition requires delineation of the lung borders, using X-ray computed tomography, radioactive gas scans ((133)Xe or (81m)Kr), or transmission scans. When quantifying regional lung deposition, the lung should be divided into outer (O) and inner (I) zones. A penetration index should be calculated, as the O/I ratio for aerosol, normalized to that for a radioactive gas or transmission scan. A variety of methods can be used to assess lung deposition and distribution. Methodology and results should be documented in detail, so that data from different centers may be compared. The use of appropriate methodology will provide greater confidence in the results of 2D imaging studies, and should allay concerns that such studies are qualitative or semiquantitative in nature.

The deposition patterns of aerosols between 0.5 and 5.0 µm showed an increase in both overall and peripheral deposition as the particle size decreased. The Onion Model allows a more complex analysis of regional deposition in preclinical models.

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