b. Bronchodilator Agents (Sympathomimetics). Sympathomimetic
bronchodilators act by relaxing contractions of the smooth muscle of the bronchioles.
These agents are often referred to as "Beta agonists".
(1) Albuterol (Proventil, Ventolin). Albuterol is a short acting beta-agonist
or bronchodilator. It is used in the relief and prevention of bronchospasm and in the
prevention of exercise-induced bronchospasm. Albuterol is available as an inhalation
aerosol, inhalation solution, inhalation capsules, regular and sustained release tablets,
and syrup. Other than the sustained release products, it is prescribed every 4 to 6
hours. Albuterol is often used as "rescue therapy" due to its quick onset of action.
(2) Salmeterol (Serevent). Salmeterol is indicated for the same conditions
as albuterol, however its distinct advantage is that it is administered twice daily. It is
available as an inhalation aerosol. Salmeterol CANNOT be used for "rescue therapy";
a short acting beta agonist such as albuterol must be used.
(3) (Epinephrine (Adrenalin). Epinephrine is used as a bronchodilator
because of its beta effects on the bronchi and a pharmacologic antagonist of histamine.
Epinephrine is employed for the treatment of acute attacks of bronchospasms
associated with emphysema, bronchitis, or anaphylaxis. The inhalation route is not the
preferred route of administration, however, it may be used. Epinephrine is usually
administered subcutaneously when used and is fairly effective at reducing
(4) Metaproterenol (Alupent, Metaprel). This is an adrenergic agent that
has primary beta2 activity. That is, its main effect is to relax the bronchioles. It has the
same indications as epinephrine. It may be used for the prevention of bronchospasms
associated with chronic obstructive pulmonary diseases. Inhalation of metaproterenol
may be used in the treatment of mild bronchospasm attacks. Metaproterenol is
somewhat more effective than inhaled isoproterenol. Metaproterenol's duration of
action is substantially longer than that of isoproterenol.
(5) Ephedrine. Ephedrine has actions of those similar to those of
epinephrine. Ephedrine is not frequently used because of the availability of other more
suitable agents. Ephedrine is administered orally. It is used to treat mild bronchospasm
attacks and prophylactically to prevent bronchospasm attacks. Ephedrine is not as
suitable as epineprhine for the treatment of severe attacks of bronchial asthma because
its bronchodilator action is weaker.
(6) Isoproterenol (Isuprel). Isoproterenol is an adrenergic agent used to
treat asthma, bronchitis, and emphysema. Like metaproterenol, isoproterenol is
administered by inhalation for the treatment of mild bronchospasms. Isoproterenol may
be administered intravenously with great caution to treat status asthmaticus.
(7) Other sympathomimetic bronchodilators include terbutaline (Brethine),
pirbuterol (Maxair), and bitolterol mesylate (Tornalate).