A metered dose inhaler, or MDI, is a small hand-held drug delivery device that dispenses doses of an aerosolized medication to the lungs. The Federal Drug Administration Center for Drug Evaluation Research classifies MDIs as a drug and device combination. The Federal Drug Administration has banned the use of chlorofluorocarbon, or CFC, propellants previously used in MDIs, causing pharmaceutical companies to switch to using inhalers with hydrofluoroalkane, or HFA, formulas.
Drug Delivery Devices
There are three types of inhalation drug delivery devices. The first is a small volume nebulizer which converts a liquid medication into aerosol particles; it is powered by compressed air. A dry powder inhaler is similar to a metered dose inhaler except that it delivers medication in a powdered form. A metered dose inhaler consists of a pressurized medication canister which fits into a plastic actuator, and delivers aerosolized medication under pressure.
Short-Acting Bronchodilators
Short-acting bronchodilators provide relief of acute, reversible airflow obstruction in individuals who suffer from obstructive pulmonary diseases such as asthma. According to the National Heart Lung and Blood Institute, these medications are also called rescue drugs. Short-acting bronchodilators in MDI form include ProAir HFA, Proventil HFA, Ventolin HFA, Xopenex HFA, Atrovent HFA and Combivent, a mixture of ipratropium bromide and albuterol sulfate. Long-acting bronchodilators are usually taken in dry powder form using a dry powder inhaler or small volume nebulizer.
Corticosteroids
Inhaled corticosteroids taken with a MDI are clinically indicated as maintenance control therapy medications for the treatment of chronic asthma. According to the National Heart Lung and Blood Institute, corticosteroids produce an anti-inflammatory response in the body. Corticosteroids dispensed in a metered dose inhaler include QVAR 40, QVAR 80, Alvesco, Aerobid, Aerobid M, Flovent HFA and Azmacort. The Pulmicort Flexihaler, the Flovent Diskus and the Asmanex Twisthaler are corticosteroid dry powder inhalers.
Combination Drugs
There are two metered dose inhalers on the market that contain a combination of two medications. These inhalers utilize a long-acting bronchodilator and a corticosteroid, providing bronchodilation and an anti-inflammatory response. These metered dose inhalers include the Advair HFA containing fluticasone and salmeterol, and the Symbicort inhaler containing budesonide and formoterol. The Advair Diskus is a dry powder inhaler.
