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2.0 What are the major classes of asthma medications?




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This article is from the Asthma FAQ, by Patricia Wrean and Marie Goldenberg mwg@radix.net with numerous contributions by others.

2.0 What are the major classes of asthma medications?


There are seven major classes of asthma medications:
- steroidal anti-inflammatories,
- non-steroidal anti-inflammatories,
- beta-agonists,
- xanthines,
- anticholinergics,
- leukotriene receptor antagonists, and
- anti-allergics.

The first two categories of drug treat the underlying
inflammation of the lung. All steroidal anti-inflammatories
are glucocorticosteroids, which are entirely different from the
anabolic steroids that have become notorious for their abuse
by athletes. There are many different corticosteroids available
for the treatment of asthma, almost all available via inhaler
to reduce the amount of side effects (see section 2.3.6). The
non-steroidal anti-inflammatories currently available are
nedocromil sodium and cromolyn sodium, though cromolyn sodium
is perhaps more properly known as a mast cell stabilizer, since
it blocks both the release of histamine and inflammatory
mediators, which means that although it blocks the inflammatory
response, it cannot reverse inflammation once it has taken place.
For this reason, I have classed it as an anti-allergic since it
is mostly commonly taken for asthma that has a strong allergy
component.

The second two classes of asthma medications, beta-agonists and
xanthines, are both bronchodilators, meaning that they relax the
muscles lining the airways, allowing the airways to expand to
their normal size. Beta-agonists are chemically related to
adrenalin, but are specifically tailored to be more effective
on the muscles of the lung while having little effect on the
muscles in the heart. They are usually taken in inhaled form,
and all but one (salmeterol) are short-acting. Theophylline,
the major xanthine, is chemically related to caffeine, since
caffeine is also a xanthine derivative, and is present in tea.
Theophylline is taken orally, often in a sustained-action form
(see section 2.4). Because its therapeutic range is close to
its toxic range, asthmatics taking theophylline should have
their blood levels monitored to ensure that their blood
concentrations of theophylline lie within the therapeutic
range (see section 2.4.1). There are some asthmatics, however,
who cannot tolerate even very low doses of theophylline.

Anticholinergics, the fourth class of medication, work by
blocking the contraction of the underlying smooth muscle of
the bronchi. Although used to treat asthma in Canada, the
anticholinergic ipratropium bromide (Atrovent) has not approved
by the US Food and Drug Administration for the treatment of
asthma, but is used for the treatment of COPD.
(It is interesting to note, however, that in the April 1982
issue of The FDA Drug Bulletin, the FDA states that "the
FD&C Act does not, however, limit the manner in which a
physician may use an approved drug. Once a product has been
approved for marketing, a physician may prescribe it for uses
or in treatment regimens or patient populations that are not
included in a approved labeling." The FD&C Act is the Food,
Drug, and Cosmetic Act.)

The newest class of asthma medications is leukotriene receptor
antagonists. My information as to how they work is sketchy,
but as I understand it, the leukotriene receptor starts off the
inflammator response of the immune system when it detects an
allergen, so presumably an antagonist would block the receptor
from responding to the presence of an allergen. Zeneca
Pharmaceuticals has just now announced that its new leukotriene
receptor antagonist, zafirlukast (Accolate), has been approved
by the FDA (the US Food and Drug Administration) and will be
available in November of 1996. Abbott Laboratories now produces
a second drug in this class: zileuton (Zyflo).

The last class, the anti-allergics, has been included because
the two anti-allergic drugs, cromolyn sodium and ketotifen, are
commonly taken for the prevention of allergic asthma. Cromolyn
sodium is a mast cell stabilizer -- it blocks the release of
histamine from mast cells, which acts to prevent asthma flares
since histamine is a very strong bronchoconstrictor. However,
it isn't considered an antihistamine because it cannot prevent
the effects of histamine once the histamine has been released
from the cell. Similarly, it blocks the release of inflammatory
mediators from the mast cell, and so prevents the inflammatory
response, although it cannot reverse inflammation once the
mediators have been released. Ketotifen fumarate (Zaditen),
a non-sedating antihistamine used mostly for the treatment of
pediatric allergic asthma, is not currently available in the
United States.


 

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