Introduction to Respiratory System

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Chapter: Medicinal Chemistry : Expectorants and Antitussives

There are many drugs acting on respiratory system, that is, antitussives, antiasthmatics, expectorants, and mucolytics.


DRUGS ACTING ON RESPIRATORY SYSTEM 

Expectorants and Antitussives

INTRODUCTION OF RESPIRATORY SYSTEM

There are many drugs acting on respiratory system, that is, antitussives, antiasthmatics, expectorants, and mucolytics. There are some drugs that act centrally for suppression of cough through the inhibition of mechano or chemoreceptors. Normally, cough is beneficial for expelling all the dust particles that enter into the respiratory tract. However, when the cough becomes severe due to any inflammation in the respiratory tract or in the lungs, it is necessary to treat with some drugs, such as mucolytics, antiasthmatics, or any expectorants.

The drugs that are used for bronchial asthma are ß2 adrenergic agonists because it is caused due to the irregulation of autonomic control towards these receptors in the lungs and respiratory tract, which produces constriction. Therefore, the difficulty in breathing persists and can be treated, especially, with ß2 adrenergic agonists. For example, salmeterol, terbutaline, formeterol, and some methyl xanthines (caffeine, theophylline) as well as anticholinergics (ipratropium bromide, tiotropium bromide). The inflammation persisting may be treated better with corticosteroids. Bronchial asthma may also be due to the hypersensitive reactions, due to the release of histamine and acetylcholine in the tracheo-bronchial regions. These can be treated by using some mast cell stabilizers called sodium chromglycate and leukotriene antagonists, that is, montelukast and zafirlukast.

Antitussives are the drugs that act in the central nervous system (CNS) to raise the threshold of  cough centre or act peripherally in the respiratory tract to reduce tussual impulse, example, opioids and non-opioids.

Mucolytics are the drugs that depolymerize the mucopolysaccharides and they break the network of tenacious sputum. These events mark the expulsion of sputum with the help of ciliary movement. Examples: bromohexine, adothoda vasaka.

Expectorants are the drugs that increase the bronchial secretion and reduce the viscosity of sputum for removal by coughing. Sodium and potassium citrate and ammonium chloride are used as expectorants.

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