Aerosol Delivery Systems

The inhaled route of administration is used for bronchodilator therapy for asthma as well as for delivery of antiinflammatory medications for allergic rhinitis and asthma. For most patients with asthma, pressurized metered-dose inhalers (pMDIs) and dry powder inhaler (DPI) devices are used for maintenance therapy but nebulizers are useful in young children and critically ill patients. Chlorofluorocarbons (CFCs) have been used as propellants in MDIs for 50 years but are now being replaced by hydrofluoralkane propellants in pMDIs because of concerns about the impact of CFCs on the ozone layer. Dry powder inhaler technology has been enhanced in recent years and modern DPIs produce aerosols of comparable quality and reproducibility as pMDIs. Aerosol quality control is important if the aerosolized medications are to be delivered in predictable quantities to the lower airways, as small changes in aerosol particle size or velocity can significantly alter lung deposition. In addition, breathing pattern and changes in airway anatomy due to disease can affect not only the quantity of medication delivered to the lung, but also its regional distribution within the lung (e.g., airway vs. alveolar deposition). Most aerosol delivery systems in current use cause significant extrapulmonary deposition of medication in the pharynx and can result in local irritation. Once extrapulmonary-deposited medication has been swallowed, it has the potential to be absorbed and cause systemic adverse events. Inhaled formulations of corticosteroids (ICS) have been developed to reduce this oral bioavailability and some preparations of ICS have negligible oral bioavailability. However it should be remembered that systemic exposure to ICS can also occur when medication that deposits in the lungs is absorbed. The delivery of aerosolized medications to children poses additional challenges. Masks used to facilitate the use of nebulizers or MDIs can also alter patterns of drug delivery. Nasal formulations of corticosteroids using aqueous suspensions or solutions and larger particles are effective at treating rhinitis.