The
anticholinergic,
antimuscarinic compounds are potent and hitherto neglected
bronchodilators. Although
atropine itself has drawbacks, principally related to its rapid absorption and consequent systemic side effects, its quaternary
ammonium congeners,
atropine methonitrate and
ipratropium bromide, are poorly absorbed. When given by inhalation, they are as effective
bronchodilators as
atropine is, but longer acting and much less prone to side effects. They act predominantly at a site that is different from
adrenergic agents and thus afford an alternative, complementary approach to the treatment of airways obstruction. In stable asthmatic subjects,
ipratropium is almost as potent a
bronchodilator as beta 2-adrenergic agents are. In patients with
chronic bronchitis and
emphysema, it is more potent than beta 2-adrenergic agents are. In both conditions, its combination with other
bronchodilators adds significantly to the level and duration of bronchodilatation. It may also be occasionally useful in counteracting
bronchospasm caused by specific stimuli, such as cold air and exercise, and particularly that caused by inadvertent beta-
adrenergic blockade. By inhalation,
ipratropium is relatively free of side effects, even in doses as much as 20 times those that produce maximal bronchodilatation. It does not significantly affect mucus production, viscosity, or clearance, problems for which
atropine is suspect. Nor does it produce
tremor and
tachycardia, as do
adrenergic agents. It can also probably be safely used in patients with
glaucoma and
bladder neck obstruction, unlike
atropine.
Ipratropium will probably find its major application in the long-term management of chronic
bronchitis and
emphysema, and in asthmatic patients who are poorly controlled by, or who experience troublesome side effects from,
adrenergic agents.