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The respiratory tract may be divided into upper and lower portions. The upper portion consists of the nose, sinuses, oropharynx, and larynx. The lower portion comprises the trachea and lungs with their associated airways. Disorders and drug therapy of the upper respiratory system differ from those of the lower respiratory tract.

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Disorders of the upper respiratory tract are those associated with infections (most commonly uncomplicated viral rhinotracheitis) and seasonal allergies (allergic rhinoconjunctivitis and rhinotracheitis). For the most part, these dysfunctions are self-limiting, and the drug classes used to treat them may be obtained without a prescription (over-the-counter, OTC). Disorders of the lower respiratory tract may be broadly classified as parenchymal infections (e.g., pneumonia) and obstructive airway (bronchial) conditions. In general, the latter disorders limit expiratory airflow. They are divided into bronchial asthma, which is characterized by acute episodes, and chronic obstructive airway disorders. Chronic obstructive airway disorders are further subdivided into chronic bronchitis, emphysema, bronchiectasis, and cystic fibrosis. The treatment of infections in all parts of the respiratory tract is discussed in Chapter 27.

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Manifestations of upper respiratory tract dysfunctions include mucous and watery discharges and vasodilation, mediated in part through histamine and other substances released from mast cells. Mast cells are important “gate-keeper” cells that are concentrated in the skin and other tissues near external body surfaces.

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Histamine is produced from the amino acid histidine and is stored in vesicles. The four histamine receptor subtypes characterized to date are designated H1 to H4. H1receptors mediate mucous discharge and vasodilation, H2 receptors are important in gastric acid secretion (Chapter 36), H3 receptors are found in the central nervous system (CNS), and H4 receptors may modulate inflammatory reactions by chemotactic effects on eosinophils and mast cells. Secretion of histamine and other mast cell mediators causes vasodilation of the nasal vasculature, leading to the nasal congestion and “runny nose” commonly associated with seasonal allergies and viral infections. Drugs used to decrease these manifestations include H1 receptor antagonists (antihistamines) to decrease mucus production and vasodilation, nasal decongestants to decrease vasodilation, and mast cell stabilizers.

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Bronchial congestion with cough and excessive mucus production are also associated with viral infections. These manifestations may be relieved with drugs that suppress coughing (antitussives) or assist in clearance of mucus from larger airways in the lungs (expectorants). The various drug classes used in therapy of the upper respiratory tract are outlined in Figure 35–1. Many of the OTC drugs are presented in Table 35–1. Mast cell stabilizers are discussed in connection with lower respiratory tract conditions.

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Figure 35–1.
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Drug classes used to treat upper airway dysfunction. Initially the drug classes are divided into histamine type 1 receptor antagonists (antihistamines), decongestants, expectorants, and antitussives. Antihistamines are divided into first and second generations. ...

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