Many respiratory drugs are given by inhalation, although enteral, parenteral, transdermal, or topical routes of administration may be used for some agents. Giving medications by the inhaled route has several advantages over systemic administration: a smaller dose can be used, adverse effects are often reduced, the drug is
delivered quickly to lung tissue or the bloodstream, administration is painless, and delivery is usually
safe and convenient.
These are the most frequently used inhaled medications. Bronchodilators can be subdivided into sympathomimetic (adrenergic) drugs and parasympatholytic (anticholinergic) drugs, as well as being classified as short acting or long acting. The adrenergic drugs stimulate the sympathetic nervous system, while anticholinergic drugs block the parasympathetic system. Adrenergic agents work to cause bronchodilation; anticholinergic drugs block bronchoconstriction. Short-acting drugs are effective for 4 to 6 hours and long-acting bronchodilators generally last about 12 hours.