Cough Chapter PDF

**Abstract** Cough, an important defensive respiratory reflex, has potentially significant adverse physical and psychological consequences and substantial economic impact. Cough is initiated by stimulation of chemically and mechanically sensitive, vagally mediated bronchopulmonary and extrapulmonar...

**Abstract** Cough, an important defensive respiratory reflex, has potentially significant adverse physical and psychological consequences and substantial economic impact. Cough is initiated by stimulation of chemically and mechanically sensitive, vagally mediated bronchopulmonary and extrapulmonary sensory nerves throughout the upper and lower respiratory tract. Cough is classified as acute, subacute, or chronic and is described as productive or nonproductive. The primary goal of self-treatment for cough is to reduce the number and severity of coughing episodes. Exclusions to the self-treatment of cough are based on signs and symptoms of potentially serious medical conditions associated with cough. *Antitussives* (i.e., cough suppressants) control or eliminate cough and are the drugs of choice for treatment of nonproductive cough. *Protussives* (i.e., expectorants) change the consistency and volume of mucus and may make it easier to expel thick, tenacious secretions. Efficacy of antitussives and protussives has been difficult to prove and may depend on the underlying cause of the cough. Product selection depends on the type of cough and underlying patient characteristics. Nonpharmacologic therapy for cough includes nonmedicated lozenges and hard candies, humidification, interventions to promote nasal drainage, and hydration. U.S. Food and Drug Administration (FDA)-approved nonprescription oral antitussives include codeine, dextromethorphan, diphenhydramine, and chlophedianol. Codeine, dextromethorphan, diphenhydramine, and chlophedianol hydrochloride act centrally on the medulla to increase the cough threshold and are indicated for the suppression of nonproductive cough caused by chemical or mechanical respiratory tract irritation. Guaifenesin (i.e., glyceryl guaiacolate) is the only FDA-approved expectorant. Guaifenesin is indicated for the symptomatic relief of acute, ineffective productive cough. Camphor and menthol are the only FDA-approved topical antitussives. Inhaled camphor and menthol vapors stimulate, then desensitize, afferent sensory neuron receptors within the nose and mucosa, creating a local anesthetic sensation and a sense of improved airflow. Cough is an important defensive respiratory reflex for airway protection. As a clinical problem, however, cough has potentially significant adverse physical and psychological consequences as well as substantial economic impact. Cough is one of the most common symptoms for which patients seek outpatient medical care.[**^1^**](https://pharmacylibrary.com/doi/full/10.21019/aphaotc-resp.cough#B1) It also is a common reason for emergency department visits. In 2019, cough was the second most common reason among children younger than 15 years for emergency department visits and the fourth most common reason for adult visits.[**^2^**](https://pharmacylibrary.com/doi/full/10.21019/aphaotc-resp.cough#B2) Nearly 11% of American adults have chronic cough.[**^3^**](https://pharmacylibrary.com/doi/full/10.21019/aphaotc-resp.cough#B3) Americans spend more than \$9.1 billion annually on nonprescription cough, cold, and related medications, more than for any other nonprescription sales category.[**^4^**](https://pharmacylibrary.com/doi/full/10.21019/aphaotc-resp.cough#B4) **Pathophysiology of Cough** Cough is initiated by stimulation of chemically and mechanically sensitive, vagally mediated bronchopulmonary and extrapulmonary sensory nerves in the pharynx, larynx, esophagus, and tracheobronchial airway epithelium.[**^5^**](https://pharmacylibrary.com/doi/full/10.21019/aphaotc-resp.cough#B5) The number of afferent nerves that are activated and the intensity of activation may influence the cough threshold. Receptors in the larynx, trachea, and proximal large airways are more sensitive to mechanical stimulation, whereas distal airway receptors are more sensitive to chemical stimulation. A complex medullary brainstem network (i.e., the "cough control center") processes the sensory input and stimulates the motor efferents. Voluntary cough is controlled by the cerebral cortex.[**^6^**](https://pharmacylibrary.com/doi/full/10.21019/aphaotc-resp.cough#B6) In viral infections, cough is mediated by a different, though not well-understood, mechanism.[**^7^**](https://pharmacylibrary.com/doi/full/10.21019/aphaotc-resp.cough#B7) The term *cough hypersensitivity syndrome* describes the proposed neural dysregulation resulting in cough associated with some chronic medical conditions.[**^6^**](https://pharmacylibrary.com/doi/full/10.21019/aphaotc-resp.cough#B6) A cough starts with a deep inspiration, followed by closure of the glottis and forceful contraction of the chest wall, abdominal wall, and diaphragmatic muscles against the closed glottis; pressure within the thoracic cavity may reach 300 mm Hg.[**^6^**](https://pharmacylibrary.com/doi/full/10.21019/aphaotc-resp.cough#B6) With reopening of the glottis, air is expelled. Peak flows during maximum voluntary cough may exceed 800 L/min, propelling mucus, cellular debris, and foreign material out of the respiratory system.[**^6^**](https://pharmacylibrary.com/doi/full/10.21019/aphaotc-resp.cough#B6) Coughing may occur in epochs ("coughing fits"). Cough, classified as *acute* (i.e., duration of \