Warren M. Zapol, MD, Professor of Anaesthesia, Harvard Medical School; Reginald Jenney Professor of Anaesthesia, Harvard Medical School; Director, Anesthesia Center for Critical Care Research, MGH, wzapol@partners.org
Warren Zapol presents his studies and views of two gases with medical therapeutic interest. Nitric oxide is inhaled by 20,000 Americans per year for neonatal persistent pulmonary hypertension and peri-operative pulmonary hypertension, and Hydrogen Sulfide is being studied in the laboratory for its ability to rapidly create metabolic arrest in rodents.
Aerosols and Aerosol Drug Delivery Systems: Basics and Beyond
Myrna Dolovich, P ENG,
Associate Clinical Professor, Medicine, Faculty of Health Sciences;
Head, Firestone Research Aerosol Laboratory/Center for Molecular Imaging
of the Lung, McMaster University, St Joseph's Healthcare, mdolovic@mcmaster.ca
Inhaled medications continue to be the most widely used form of therapy for treating respiratory disease in adults and children. Developments in inhaler technology and design have led to improvements in the production of therapeutic aerosols and with greater efficiencies of delivery and ease of use from the variety of inhalers available. Novel designs continue to be approved by the regulatory agencies and commercialized by manufacturers and, as a result, numerous delivery systems are currently available for drugs administered in aerosol form. Devices range from hydrofluoroalkane (HFA) pressurized metered-dose inhalers (pMDIs) with and without attached spacer devices, dry powder inhalers (DPIs), and nebulizers for providing continuous or intermittent aerosols of liquid solutions or suspensions. Within these three categories are a variety of devices producing aerosols with somewhat similar characteristics but with a range of fine particle lung delivery efficiencies, the current indicator of lower respiratory tract deposition and anticipated clinical advantage.
Delivering aerosolized medications to the lung is a challenge: the combination of drug formulation properties, delivery system characteristics, patient ventilatory technique and compliance, and the nature of the lung disease all influence the success of therapy.
The dose of drug deposited in the lower
respiratory tract is affected by the inhalation technique adopted by
the patient (inspiratory flow rate, inspiratory volume, and breath-hold
time). Most importantly, the degree of airway narrowing, which varies
with the type and severity of the lung disease, further influences the
distribution of that dose within the lung and potentially, the response
to the therapy.
In the last 10–15 years, major design changes have occurred in all three categories of drug delivery devices. Examples of Innovative features introduced into newer types of inhalers are dose counters and integrated electronic management systems to track treatments and maintain treatment schedules, all designed with a view to improve compliance.
Aerosol products for the treatment of respiratory diseases have the simple advantage of depositing a specific drug directly to the appropriate receptors, thus bypassing GI barriers and general systemic exposure. Inhalers should provide a predictable, consistent dose of drug, operate in a patient friendly manner, and provide a reasonable cost of treatment per day. The patient must be able to use their device easily, maintain it and derive clinical benefit from the drug provided from the system. Physicians and patients must also recognize that if one system does not work, an alternative can be tried.
Comments