6. DRUGS AFFECTING THE RESPIRATORY SYSTEM

6.1. ANTITUSSIVES AND

EXPECTORANTS

Cough is a reflex act occurring in response to irritation of the respiratory tract and aiming to remove bronchial gland mucus and foreign bodies. It may be caused by mechanical or chemical irritants, or by central stimuli. The afferent part of the reflex arc conducts a nerve impulse from receptors located in the mucosa of the larynx, trachea, and bronchi, to the coughing center of the medulla oblongata, and causes its excitation. The flow of impulses passes along the efferent part of the reflex arc to the respiratory muscles causing specific contractions of intercostal muscles and the diaphragm (fig. 6.1).

Fig. 6.1. Peripheral receptors located in the epithelium of the larynx, trachea and bronchi react to mechanical and chemical irritants. The nerve impulse is conducted along the afferent fibers from the receptors to the cough center of the medulla oblongata and causes its excitation. Efferent part of the reflex arc carries the flow of impulses to the respiratory muscles causing specific contractions of the intercostal muscles and the diaphragm

Cough is a protective mechanism but can require treatment when it becomes exhausting.

A distinction is made between two types of cough:

• productive ("wet") cough is accompanied by expectoration, removal of foreign bodies, mucus, and microorganisms. Productive cough performs a protective function and should not be suppressed. Mucolytic drugs are prescribed to reduce viscosity of the sputum;

• non-productive ("dry") cough is not accompanied by expectoration; it does not perform a protective function, and exhausts the patient. Depending on pathogenesis, non-productive cough is treated with medications intended for suppression of cough reflex and changing the quantity or viscosity of the sputum.