ANTIASTHMATIC AGENTS relieve the symptoms of bronchial asthma or prevent recurrent attacks. The symptoms of asthma include bronchoconstriction (obstructive airways disease), often with over-secretion of fluid within the bronchioles and other breathing difficulties. Two main types of drugs are used: the first to treat acute attacks; and the second as prophylactics to prevent attacks.

BRONCHODILATORS, which are SMOOTH MUSCLE RELAXANTS, work by dilating and relaxing the bronchioles. The most commonly used are the β-receptor stimulant drugs (which are SYMPATHOMIMETICS) , notable examples include salbutamol and terbutaline. See also β-ADRENOCEPTOR AGONISTS. The β-adrenoceptor agonists are most commonly given by inhalation, and are mainly used for treating acute attacks (or immediately before exertion in exercise asthma), and are largely of the β2-adrenoceptor agonist type. Other bronchodilator drugs, which work directly on the bronchioles, include theophylline.

The second group of antiasthmatics are ANTHNFLAMMATORY or ANTIALLERGIC AGENTS, such as the CORTICOSTEROIDS and sodium cromoglycate. These drugs prevent the release of local inflammatory mediators, which contribute to attacks, so preventing asthma attacks, and also provide symptomatic relief.

There are some other drugs, such as ketotifen (a drug that blocks a number of receptor types) and ipratropium bromide (an anticholinergic agent — a MUSCARINIC CHOLINOCEPTOR ANTAGONIST) that may occasionally be used (for instance, when the other types of drug are ineffective for some reason). LIPOXYGENASE INHIBITORS (e.g zileutin) represent a new type of antiinflammatory agent and are under clinical development, and in trials have shown improved pulmonary function.