Drugs for Cough

Drugs of cough

There are two sorts of cough:
 productive (the useful) when it expels secretions or foreign material from the respiratory tract
 Useful cough should be allowed to serve its purpose and suppressed only when it is exhausting the patient or is dangerous, e.g. after eye surgery.
 unproductive and persistent( the useless )
 Useless persistent cough should be stopped.


asthma, rhinosinusitis, esophageal reflux
SITES OF ACTION FOR TREATMENT
Peripheral sites
On the afferent side of the cough reflex: by reducing input of stimuli from throat, larynx, trachea a warm moist atmosphere has a demulcent effect on the pharynx.
On the efferent side of the cough reflex: to render secretions more easily removable (mucolytics)
The best antitussive of all :is removal of the cause of the cough itself, e.g. treatment of underlying conditions such as
 asthma
 postnasal drip
 gastroesophageal reflux.
 In patients with hypertension or cardiac failure, a common cause of a dry cough is treatment with an ACE inhibitor.


COUGH SUPPRESSION
Antitussives
1. Peripheral antitussives
2. Central antitussives

Peripheral antitussives

 Demulcents that soothingly coat the pharynx
 Linctus (mainly sugar-based syrup).
 Lozenges
 Inhalation
 Water aerosol inhalation
 Benzoin to give the inhalation a therapeutic smell (aromatic inhalation)
 Local anaesthetics block the mucosal cough receptors (modified stretch receptors) directly ,Nebulised lignocaine reduces coughing
 during some type of bronchoscopy
 in the cough that accompany bronchial carcinoma.

centrally acting Antitussives

The opioid analgesics are among the most effective drugs for the suppression of cough (medullary cough centre itself)
 at doses below those necessary to produce analgesia.
 The receptors involved in the antitussive effect differ from those associated with the other actions of opioids).
The opioid derivatives used as antitussives are dextromethorphan, codeine, and noscapine
methadone or diamorphine linctus preferred in patients with advanced bronchial carcinoma
pholcodine, ( nonsedating and nonaddictive), is widely used


Dextromethorphan,
 it is NMDA receptor antagonist
 free of addictive properties and produces less constipation than codeine.
 The usual antitussive dose is 15-30 mg three or four times daily.
Codeine, has antitussive action at doses lower than those required for analgesia. Thus, 15 mg are usually sufficient to relieve cough.
Antihistamines: Sedation reduces the sensitivity of the cough reflex. older sedating antihistamines,
e.g. diphenhydramine often the doses needed causes drowsiness so that combination with other drugs, such as pholcodine and dextromethorphan,
In children cough is nearly always useful and sedation at night is more effective than is codeine.
A sedative antihistamine (e.g. promethazine), sputum thickening may be a disadvantage.

MUCOLYTICS AND EXPECTORANTS

Respiratory mucus consists largely of water and its slimy character is due to glycoproteins cross-linked together by disulphide bonds.
In pathological states much more mucus may be produced; an exudate of plasma proteins which bond with glycoproteins and form larger polymers results in the mucus becoming more viscous.
A mucolytic drug: is a drug that breaks down thick mucus, making it thinner and easier to cough out.
Carbocisteine and mecystine
 MOA :have free sulphydryl groups that open disulphide bonds in mucus and reduce its viscosity.
 orally administrated or by inhalation
 uses :when viscous secretion is a problem (cystic fibrosis)
 side effects:gastrointestinal irritation and allergic reaction.
Bromhexine
 Thinning & fragmentation of mucopolysaccaride fibers
 ↑ volume & ↓ viscosity of sputum


Dornase alfa is phosphorylated glycosylated recombinant human deoxyribonuclease.
MOA : hydrolyzes the DNA present in sputum/mucus of cystic fibrosis patients and reduces viscosity in the lungs
 It is given daily by inhalation
Expectorants
encourage productive cough by increasing the volume of bronchial secretion;
The group includes:
 guaiphenesin
 Ipecacuanha
 volatile oils
Guaiphenesin Expectorant drug usually taken by mouth available as single & also in combination
MOA=Increase the volume & reduce the viscosity of secretion in trachea & bronchi

Choice for drug therapy for cough

• Simple suppression of useless cough
Codeine, pholcodine, dextromethorphan and methadone
In pertussis infection (whooping cough), codeine and atropine
• To increase bronchial secretion slightly and to liquefy what is there
Water aerosol with or without menthol and benzoin inhalation, or menthol and eucalyptus inhalation may provide comfort harmlessly.
Carbocysteine or another mucolytic orally may occasionally be useful.
• Cough originating in the pharyngeal region
lozenges or demulcents are used.


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