Cough centres

It is a reduction/decrease in the activity of specialized cells. For example barbiturates depress central nervous system, quinidine depresses myocardium. Certain drugs stimulate one type of cells but depress others e.g. morphine stimulates the vagus and chemoreceptor trigger zone but depresses the vomiting and cough centres. Similarly acetylcholine stimulates intestinal smooth muscle but depresses SA node in the heart. 

Effect on CNS The main action of morphine is CNS depression which further results in analgesia, depression of respiratory centre, cough centre and sleep. In addition it causes euphoria or dysphoria and dependence. 

Action on cough centre Morphine suppresses cough reflexes, but cough suppression by opioids may allow accumulation of respiratory secretions and may produce airway obstruction. 

They are central cough suppressants and act centrally to raise the threshold of cough centre and inhibit the cough reflex by... 

Codeine, which is an opium alkaloid is most commonly opiate used as antitussive and more selective for cough centre. Like morphine, it depresses cough centre but is less constipating and abuse liability is low. It is relatively safe drug used in cough along with analgesic property and it s only important adverse effect is constipation. 

Many antihistaminics have been added to antitussive/expectorant formulations. They do not act on cough centre but provide relief due to their sedative and anticholinergic action. 

Pholcodine, a related drug (opioid), is relatively selective in its depressive effect on the cough centre (affecting the respiratory centre less),... 

Opium alkaloids act on the cough centre in the brain to depress the cough reflex. Both dextro- and laevo-isomers of opioid compounds possess antitussive activity, but only the laevo-isomers have liability for dependence. 

The phytomedicines that inhibit the cough-centre Codeine, glaucine, noscapine and semisynthetic ethyphine. The phytomedicines that inhibit the cough-reflex Mucilaginous herbs such as Althea root and Icelandic moss. 

Morphine is also stiU in use today for extreme pain, as in cases of severe burns or open fractures, where its application is limited to emergencies, because of the significant risk of addiction. Conversely (+)-morphine, like (+)-codeine or (+)-heroin, possesses no analgesic effect. By comparison with (-)-morphine, (-)-codeine is much less effective however, it inhibits selectively the cough centre, and has a substantially lower potential for addiction. It is therefore the main component of many cough syrups. Thebaine, on the other hand, produces like strychnine severe convulsions, and finds therefore no therapeutic applica-... 

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