Dear students, today our topic of discussion is “Drugs used in Cough”.
We are discussing this topic to understand cough, its types and mechanism of action of drugs used in cough.
After reading this topic you will be able to understand how to judicially use anti cough drugs and what are their adverse effects.
So usually “cough” is a protective reflex in our body and it tries to expel the respiratory secretions or foreign particles from air passage.
It can be divided into (I) Productive and (II) Non productive cough (i.e. dry cough).
(I)Productive cough – It means Production of excessive sputum. In this type of cough Antitussive drugs (Drugs which suppress cough reflex) should not be used. The approach should be to reduce the viscosity and increase production of secretions so it can be expelled easily, and that’s why “expectorants” are used which we will discuss later.
(II) Non productive cough (i.e. dry cough). –
it serves no useful purpose. It should be suppressed and thus “antitussive” should be used.
Now we move forward towards classification:-
(1)Pharyngeal Demulcents:-
They are the substances which soothe the throat by a protective covering on throat (Pharynx) and provide relief by reducing impulses from inflamed or irritated mucosa
Lozenges (you know strepsils, vicks tablet etc.)
Honey (remember your parents advising you to have honey and ginger in mouth for cough)
Glycerine etc.
(2)Expectorants :-
These drugs act by increasing the volume or decrease the viscosity of bronchial secretions/mucus (or both) and make easy to expel the secretions and provide relief.
Expectorants can be divided into
(I)Mucokinetics –
As we can understand by the name “Mucokinetics” they stimulate the outflow of serrations ( by increasing the volume of secretions and/or by stimulation and outward mucociliary movements)
Eg- Guaiphenesin (plant product, FDA approved OTC drug for expectorant use, Increased secretions and ciliary action)
-Tolu balsam (plant product MOA, same as Guipenasin)
-vasaka (plant product MOA, same as Guipenasin)
-sodium/potassium citrate (increase secretion by salt action)
– Potassium iodide (act by irritating mucosa) (remember whenever iodine is involved anywhere thyroid functions may impair)
– Ammonium chloride (nauseating property so reflexly increase respiratory secretions)
(II)Mucolytics –
They decrease the viscosity of mucous and facilitate its removal by cough reflex .
That’s why in Expectorants cough reflex should not be abolished.
Bromhexine – Depolymerised mucopolysaccharides in mucous and make it thin for expulsion
Main S.E. are rhinorrhoea, lacrimation,hypersensitivity, gastric irritation
Ambroxol– metabolite of bromhexine, same MOA and S.E.
Acetylcysteine– Act on disulfide bond of mucoprotein presents in sputum and make it less visid (thin). It can be used orally or by inhalation.
(Remember same drug is used in acute paracetamol poisoning where it can be used by I.V. route or orally )
Carbocysteine etc.
(3)Antitussive-
Raise the CNS threshold of cough centre.
Can be used only in dry (unproductive) cough or when cough is harmful and need to be suppressed eg. After surgery. Blocking of productive cough with a powerful antitussive like opioids can cause accumulation of secretions further lead to airway obstruction and atelectasis.
(I)Opioids-
Codeine- more selective to cough centre, low abuse liability then morphine and main side effect is constipation and as like morphine at higher dose it cause drowsiness and respiratory depression and thus use cautiously in drivers and people need attention during work and due to respiratory depression it is contraindicated in asthmatics.
While Pholcodine has no addictive properties and efficacy similar to codeine and longer acting also
Noscapine is also opioid alkaloids with no addictive property but can release histamine and cause bronchoconstriction in asthmatics
(II)Non Opioid antitussive
Dextromethorphan– as effective as codeine, devoid of constipation and abuse liability (unlike codeine)
But can produce drowsiness, nausea and ataxia.
(4)Antihistaminics:-
No direct effect on cough but can be effective in allergic conditions and relief in other type of cough is due to their anticholinergic and sedative effects (and that’s why first generation antihistaminics are used ) eg. Chlorpheniramine, Diphenhydramine, Promethazine
(5)Bronchodilators-
In bronchial hyperreactivity (like asthma) leads to cough due to bronchoconstriction and bronchodilators like Salbutamol or terbutaline etc. are used.
In nutshell
If a patient approaches you with a cough and if it is more than two weeks then sputum examination for Acid fast bacilli (AFB)smear and culture should be sent.
Always treat cough as a symptom.
Viral cough (usually non-productive) subside itself within a week or two and demulcents are useful and sufficient for relief.
If you want to suppress the non productive cough then use antitussives like Dextromethorphan/ noscapine/ pholcodine/codeine
If cough is productive then guaiphenesin/ ambroxol/bromhexine etc. Expectorants can be used although it is also seen that liquid sputum is hard to expel out by mucociliary action and thus only guaifenesin is only FDA approved OTC drug for expectorant use.
FDA also recommends that OTC cough and cold agents (eg, products containing antitussives, expectorants, decongestants, and antihistamines) not be used in infants and children younger than 2 year.
Happy learning….. Have a great time
