HOW DO ANTITUSSIVES WORK? 

Antitussives are prescription or over-the-counter drugs used for suppressing cough. 

Antitussives act on the cough center in the brain and decrease the sensitivity of cough receptors. When the cough receptors in the respiratory passages and lungs are stimulated, they send signals to the cough center located in the brain. The impulse generated travels down and stimulates the respiratory muscles to produce a cough.  

Antitussives relieve cough by: 

Acting on the cough center in the brain 

Decreasing the sensitivity of cough receptors 

Interrupting cough impulse transmission 

Numbing the cough receptors in the respiratory passages and lungs

WHAT ARE NAMES OF ANTITUSSIVES? 

Generic and brand names of antitussives include: 

mechanism action Antitussive

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Antitussives are cough suppressants. There are two ways to inhibit coughing: centrally and peripherally.

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Cough is normally produced through the stimulation of sensory receptors (https://www.sciencedirect.com/topics/medicine-and-dentistry/sensory-receptor) of the glossopharyngeal and vagus nerves (https://www.sciencedirect.com/topics/medicine-and-dentistry/vagus-nerve), innervating the mucous membranes (https://www.sciencedirect.com/topics/medicine-and-dentistry/mucosa) of the lower pharynx (https://www.sciencedirect.com/topics/medicine-and-dentistry/pharynx), larynx (https://www.sciencedirect.com/topics/medicine-and-dentistry/larynx), trachea, and smaller airways of the respiratory system. The receptors then transmit the signal to the cough center in the brain, which then triggers a reflex motor response that results in contraction of the muscles to close the glottis (https://www.sciencedirect.com/topics/medicine-and-dentistry/glottis) (vocal cords) and contraction of the muscles of expiration. The result is a sudden increase in intrathoracic pressure, followed by relaxation of the vocal cords (https://www.sciencedirect.com/topics/medicine-and-dentistry/vocal-folds), resulting in rapid expulsion of air (Figure 12-1).

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Centrally acting agents such as dextromethorphan work by inhibiting the cough center in the brain, elevating the threshold for coughing. The exact mechanism by which they do this is still poorly understood. Dextromethorphan, for example, is an N-methyl-d-aspartate (NMDA) antagonist, although it is not known what contribution this has to its antitussive effects.

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Opiates such as codeine and hydrocodone also work through a central mechanism.

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Peripheral-acting agents work either by anesthetizing the local nerve endings (https://www.sciencedirect.com/topics/medicine-and-dentistry/nerve-ending) or acting as demulcents (https://www.sciencedirect.com/topics/medicine-and-dentistry/demulcent-agent). Demulcents have a soothing effect on the throat.

In 1946 and 1947 The racemic parent compound racemorphan was first described in a Swiss and US patent application from Hoffmann-La Roche 

In 1950,  a patent was granted .

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 In 1952,A resolution of the two isomers of racemorphan with tartaric acid was published ,and dextromethorphan was successfully tested in 1954 as part of US Navy and CIA-funded research on nonaddictive substitutes for codeine.

Dextromethorphan was approved by the FDA in 1958 as an over-the-counter antitussive. As had been initially hoped, dextromethorphan was a solution for some of the problems associated with the use of codeine phosphate as a cough suppressant, such as sedation and opiate dependence, but like the dissociative anesthetics phencyclidine and ketamine, dextromethorphan later became associated with nonmedical use