Drugs for Respiratory System Disorders Prepared By I Gede Purnawinadi, S.Kep., M.Kes.

Preview The respiratory system is one of the most important organ systems; a mere 5 to 6 minutes without breathing may result in death. When functioning properly, this system provides the body with the oxygen critical for all cells to carry on normal activities. The respiratory system also provides a means by which the body can rid itself of excess acids and bases. This chapter examines drugs used to treat conditions associated with the upper respiratory tract: allergic rhinitis, nasal congestion, and cough, pharmacotherapy of asthma and chronic obstructive pulmonary disease, conditions that affect the lower respiratory tract.

Physiology of the Upper Respiratory Tract The upper respiratory tract (URT) consists of the nose, nasal cavity, pharynx, and paranasal sinuses. These passageways warm, humidify, and clean the air before it enters the lungs. The nasal mucosa is also part of the first line of body defense. Up to a quart of nasal mucus is produced daily, and this fluid is rich with immunoglobulins that are able to neutralize airborne pathogens.

Allergic Rhinitis Allergic rhinitis, or hay fever, is inflammation of the nasal mucosa due to exposure to allergens. Although not life threatening, allergic rhinitis is a condition affecting millions of patients, and pharmacotherapy is frequently necessary to control symptoms and to prevent secondary complications.

Allergic Rhinitis Symptoms of allergic rhinitis resemble those of the common cold: tearing eyes, sneezing, nasal congestion, postnasal drip, and itching of the throat. In addition to the acute symptoms, potential complications of allergic rhinitis include loss of taste or smell, sinusitis, chronic cough, hoarseness, and middle ear infections in children. As with other allergies, the cause of allergic rhinitis is exposure to an antigen. An antigen, or allergen, may be defined as anything that is recognized as foreign by the body’s defense system.

Allergic Rhinitis The fundamental pathophysiology responsible for allergic rhinitis is inflammation of the mucous membranes in the nose, throat, and airways. The nasal mucosa is rich with mast cells (a type of connective tissue cell) and basophils (a type of leukocyte), which recognize antigens as they enter the body. Patient with allergic rhinitis contain greater numbers of mast cells. An immediate hypersensitivity response releases histamine and other inflammatory mediators from the mast cells and basophils, producing sneezing, itchy nasal membranes, and watery eyes. A delayed hypersensitivity reaction also occurs 4 to 8 hours after the initial exposure, causing continuous inflammation of the mucosa and adding to the chronic nasal congestion experienced by these patients. Because histamine is released during an allergic response, many signs and symptoms of allergy are similar to those of inflammation

Pharmacotherapy of Allergic Rhinitis The therapeutic goals of treating allergic rhinitis are to prevent its occurrence and to relieve symptoms. Thus, drugs used to treat allergic rhinitis may be grouped into two simple categories: Preventers are used for prophylaxis and include antihistamines, intranasal corticosteroids, and mast cell stabilizers. Relievers are used to provide immediate, though temporary, relief for acute allergy symptoms once they have occurred. Relievers include the oral and intranasal decongestants, usually drugs from the sympathomimetic class.

Antihistamines In addition to treating allergic rhinitis with drugs, nurses should help patients identify sources of the allergies and recommend appropriate interventions. These may include removing pets from the home environment, cleaning moldy surfaces, using microfilters on air conditioning units, and cleaning dust mites out of bedding, carpet, or couches. The histamine receptors responsible for allergic symptoms are called H1 receptors. Antihistamines are drugs that selectively block histamine from reaching its H1 receptors, thereby alleviating allergic symptoms. A large number of H1-receptor antagonists are available as medications.

Intranasal Corticosteroids Corticosteroids, also known as glucocorticoids, are applied directly to the nasal mucosa to prevent symptoms of allergic rhinitis. They are administered with a metered-spray device that delivers a consistent dose of drug per spray. When sprayed onto the nasal mucosa, corticosteroids decrease the secretion of inflammatory mediators, reduce tissue edema, and cause a mild vasoconstriction.

Decongestants Decongestants are drugs that relieve nasal congestion. They are administered by either the oral or intranasal routes and are often combined with antihistamines in the pharmacotherapy of allergies or the common cold. Most decongestants are sympathomimetics: drugs that activate the sympathetic nervous system. Activity are effective at relieving the nasal congestion associated with the common cold or allergic rhinitis.

COMMON COLD The common cold is a viral infection of the upper respiratory tract that produces a characteristic array of annoying symptoms. Therapies used to relieve symptoms include some of the same drug classes used for allergic rhinitis, including antihistamines and decongestants. A few additional drugs, such as those that suppress cough and loosen bronchial secretions, are used for symptomatic treatment.

Antitussives Antitussives are drugs used to dampen the cough reflex. They are of value in treating coughs due to allergies or the common cold. Cough is a natural reflex mechanism that serves to forcibly remove excess secretions and foreign material from the respiratory system. Dry, hacking, nonproductive cough, however, can be irritating to the membranes of the throat and can deprive a patient of much-needed rest. It is these types of conditions in which therapy with medications that control cough, known as antitussives, may be warranted.

Expectorants and Mucolytics Several drugs are available to control excess mucus production. Expectorants increase bronchial secretions, and mucolytics help loosen thick bronchial secretions. Expectorants are drugs that reduce the thickness or viscosity of bronchial secretions, thus increasing mucus flow that can then be removed more easily by coughing. Drugs available to directly loosen thick, viscous bronchial secretions. Drugs of this type, which are called mucolytics, break down the chemical structure of mucus molecules. The mucus becomes thinner and can be removed more easily by coughing.

Physiology of the Lower Respiratory Tract The primary function of the respiratory system is to bring oxygen into the body and to remove carbon dioxide. The process by which gases are exchanged is called respiration. Ventilation is the process of moving air into and out of the lungs. As the diaphragm contracts and lowers in position, it creates a negative pressure that draws air into the lungs, and inspiration occurs. During expiration, the diaphragm relaxes and air leaves the lungs passively with no energy expenditure required. Ventilation is a purely mechanical process that occurs approximately 12 to 18 times per minute in adults. This rate may be modified by a number of factors, including emotions, fever, stress, the pH of the blood, and certain medications.

Bronchiolar Smooth Muscle Bronchioles are muscular, elastic structures whose diameter, or lumen, varies with the contraction or relaxation of smooth muscle. Bronchodilation opens the lumen, allowing air to enter the lungs more freely, thus increasing the supply of oxygen to the body’s tissues. Bronchoconstriction closes the lumen, resulting in less airflow. Bronchodilation and bronchoconstriction are largely regulated by the two branches of the autonomic nervous system: The sympathetic branch activates beta2-adrenergic receptors, which causes bronchiolar smooth muscle to relax, the airway diameter to increase, and bronchodilation to occur. The parasympathetic branch causes bronchiolar smooth muscle to contract, the airway diameter to narrow, and bronchoconstriction to occur.

Administration of Pulmonary Drugs Via Inhalation Drugs that enhance bronchodilation will enable the patient to breathe easier. Drugs that stimulate beta2- adrenergic receptors, commonly called bronchodilators, are some of the most frequently prescribed drugs for treating pulmonary disorders. The enormous surface area of the bronchioles and alveoli, and the rich blood supply to these areas, results in an almost instantaneous onset of action for inhaled substances. Medications are delivered to the respiratory system by aerosol therapy. An aerosol is a suspension of minute liquid droplets or fine solid particles suspended in a gas.

ASTHMA Asthma is a chronic pulmonary disease with inflammatory and bronchospasm components. Drugs may be given to decrease the frequency of asthmatic attacks or to terminate attacks in progress. Characterized by acute bronchospasm, asthma can cause intense breathlessness, coughing, and gasping for air. Along with bronchoconstriction, an acute inflammatory response stimulates histamine secretion, which increases mucus and edema in the airways. As in allergic rhinitis, the airway becomes hyper-responsive to allergens. Both bronchospasm and inflammation contribute to airway obstruction.

BRONCHODIALATORS FOR TREATING ASTHMA Beta-Adrenergic Agonists Beta2-adrenergic agonists (or simply beta agonists) are effective bronchodilators for the management of asthma and other pulmonary diseases. They are first-line drugs for the treatment of acute bronchoconstriction. Anticholinergics Anticholinergics (also called cholinergic blockers or antagonists) are alternative bronchodilators for patients who are unable to tolerate the beta2-adrenergic agonists. Methylxanthine The methylxanthines were considered drugs of choice for treating asthma 30 years ago. The methylxanthines, theophylline (Theo-Dur, others) and aminophylline (Truphylline), are bronchodilators chemically related to caffeine. Corticosteroids Corticosteroids, also known as glucocorticoids, are the most potent natural anti- inflammatory substances known.

Pharmacotherapy of COPD Chronic obstructive pulmonary disease (COPD) is a progressive pulmonary disorder characterized by chronic and recurrent obstruction of airflow. COPD is a major cause of death and disability. The three specific COPD conditions are asthma, chronic bronchitis, and emphysema. The goals of pharmacotherapy of COPD are to relieve symptoms and avoid complications of the condition. Various classes of drugs are used to treat infections, control cough, and relieve bronchospasm. Most patients receive bronchodilators such as ipratropium (Atrovent), beta2 agonists, or inhaled corticosteroids.