2.0 What are the major classes of asthma medications?

There are seven major classes of asthma medications:

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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