In this paper I hope to provide readers with an understanding of the factors that significantly affect the quantity of medication delivered by the various inhalation devices available. I also suggest an approach to changing patients from the current pressurized metered dose inhalers (pMDIs), containing chlorofluorohydrocarbons (CFC) that will not be available indefinitely, to the newer inhalation devices now being introduced.
During the past 20 years the inhaled route for delivery of medications for the treatment of asthma has gradually supplanted the oral route as the preferred method of drug delivery for most patients. This was in large part due to the efficacy and ease of use of the widely prescribed pMDIs containing CFCs as a propellant. Such rapid and direct delivery of medication to the target tissue greatly reduces the dose of medication and the frequency and severity of adverse effects. As a consequence of an international treaty to protect the atmospheric ozone layer (Montreal Protocol on Substances That Deplete the Ozone Layer), CFCs are gradually being replaced as the preferred propellant for the delivery of medication to the airways of patients with obstructive airways disease. Patients currently using CFC-based pMDIs will have to change either to a pMDI that uses the newer, more environmentally friendly, propellant gases or to a multidose dry powder inhaler device (DPIs). This switch will require education of patients and determination of the therapeutic equivalence of drugs when substituting one device for another, or one type of medication for another within each class of drug.