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Asthma is a disease characterized by airway inflammation and episodic, reversible bronchospasm. Drugs useful in asthma include bronchodilators (smooth muscle relaxants) and anti-inflammatory drugs. Bronchodilators include sympathomimetics, especially β2-selective agonists, muscarinic antagonists, methylxanthines, and leukotriene receptor blockers. Anti-inflammatory drugs used in asthma include corticosteroids, mast cell stabilizers, and an anti-IgE antibody. Leukotriene antagonists play a dual role. Chronic obstructive pulmonary disease (COPD) is characterized by airflow limitation that is less reversible than in asthma and by a progressive course. However, many of the same drugs are used.
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The immediate cause of asthmatic bronchoconstriction is the release of several mediators from IgE-sensitized mast cells and other cells involved in immunologic responses (Figure 20–1). These mediators include the leukotrienes LTC4 and LTD4. In addition, chemotactic mediators such as LTB4 attract inflammatory cells to the airways. Finally, several cytokines and some enzymes are released, leading to chronic inflammation. Chronic inflammation leads to marked bronchial hyperreactivity to various inhaled substances, including antigens, histamine, muscarinic agonists, and irritants such as sulfur dioxide (SO2) and cold air. This reactivity is partially mediated by vagal reflexes. COPD is often triggered by upper respiratory infection (like asthma) but occurs in older patients (usually long-term smokers) and is poorly reversible with bronchodilators.
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Acute bronchospasm must be treated promptly and effectively with bronchodilators ("reliever" drugs). Beta2 agonists, muscarinic antagonists, and theophylline and its derivatives are available for this indication. Long-term preventive treatment requires control of the inflammatory process in the airways ("controller" drugs). The most important anti-inflammatory drugs in the treatment of chronic asthma are the corticosteroids. Long-acting β2...