Respiratory drugs bronchial asthma

W ithin the past few years a number of new drugs have been introduced to treat respiratory disorders, such as bronchial asthma and disorders that produce chronic airway obstruction. This chapter discusses the bronchodilators, dragp that have been around for a long time but are still effective in specific instances, and the newer antiasthma drugs that have proven to be highly effective in the prophylaxis (prevention) of breathing difficulty. 

A broncho dilator is a drug used to relieve bron-chospasm associated with respiratory disorders, such as bronchial asthma, chronic bronchitis, and emphysema These conditions are progressive disorders characterized by a decrease in die inspiratory and expiratory capacity of die lung. Collectively, tiiey are often referred to as COPD. The patient with COPD experiences dyspnea (difficulty breatiiing) with physical exertion, has difficulty inhaling and exhaling, and may exhibit a chronic cough. 

Bronchial asthma is defined as a chronic inflammatory disease of the lungs it affects an estimated 9 to 12 million individuals in the U.S. Furthermore, its prevalence has been increasing in recent years. Asthma is characterized by reversible airway obstruction (in particular, bronchospasm), airway inflammation, and increased airway responsiveness to a variety of bronchoactive stimuli. Many factors may induce an asthmatic attack, including allergens respiratory infections hyperventilation cold air exercise various drugs and chemicals emotional upset and airborne pollutants (smog, cigarette smoke). 

Although anticholinesterase agents can be used in the treatment of atony of the bladder and adynamic ileus, they are contraindicated in cases of mechanical obstruction of the intestine or urinary tract. Caution should also be used in giving these drugs to a patient with bronchial asthma or other respiratory disorders, since they will further constrict the smooth muscle of the bronchioles and stimulate respiratory secretions. 

Certain forms of dyspnea yield only to opiates. Especially in this category is the dyspnea of acute left ventricular failure and pulmonary edema. Most authorities agree that morphine is contraindicated in patients with pulmonary edema caused by chemical respiratory irritants. If needed in such cases for severe pain, its use should be combined with oxygen inhalation and positive-pressure therapy. In bronchial asthma, morphine is usually contraindicated because there is danger of addiction, the drug tends to depress respiration and to constrict bronchioles, and patients with asthma may be allergic to the drug. Deaths have occurred from the use of morphine in asthma. 

Respiratory disease may often be traced to an external source such as an inhaled allergen, pathogen, particulate matter, chemical irritant, or other, undefined material. Ideally, the resulting disease state would be abolished by removing the suspect material from the environment however, often this is not possible. We are left then to define effective drugs for the treatment of bronchial asthma, chronic bronchitis, chronic pulmonary emphysema, and a variety of other debilitating respiratory diseases. 

Three factors contribute to airway obstruction in asthma (1) contraction of the smooth muscle that surrounds the airways (2) excessive secretion of mucus and in some, secretion of thick, tenacious mucus that adheres to the walls of the airways and (3) edema of the respiratory mucosa. Spasm of the bronchial smooth muscle can occur rapidly in response to a provocative stimulus and likewise can be reversed rapidly by drug therapy. In contrast, respiratory mucus accumulation and edema formation are likely to require more time to develop and are only slowly reversible. 

Bronchial smooth muscle contains B2 receptors that cause relaxation. Activation of these receptors results in bronchodilation (see Chapter 20 Drugs Used in Asthma and Table 9-3). The blood vessels of the upper respiratory tract mucosa contain receptors the decongestant action of adrenoceptor stimulants is clinically useful (see Clinical Pharmacology). 

The p2-adrenergic receptor gene mutations have, therefore, been associated with a wide spectrum of respiratory phenotypes that include altered drug responses and bronchial hyperreactivity disease. The [l2-adrcncrgic receptor polymorphisms probably represent only a few of the genetic variables involved in asthma pathophysiology [157,165]. There may be potential to use these variants more widely to personalize diagnosis and treatment options. 

Xanthines are a group of drugs that directly cause relaxation of bronchial smooth muscle and some central respiratory stimulation. They also have a slight diuretic effect. Xanthines are of principle use in the immediate phase reaction of asthma but also have some effect on the late phase reaction. They are used to treat severe acute asthma attacks and chronic asthma, in particular control of nocturnal asthma and early morning wheezing. Xanthines also have some use in chronic bronchitis. 

Spector SL. Leukotriene activity modulation in asthma. Drugs 1997 54(3) 369-384. Determinants of bronchial responsiveness in the European Community Respiratory Health Survey in Italy evidence of an independent role of atopy, total serum IgE levels, and asthma symptoms. Allergy 1998 53(7) 673-681. 

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