Cough is a protective reflex caused by stimulation of sensory nerves in the respiratory tract mucosa. It serves to expel respiratory secretions induced by infections or irritants like smoke. There are three main types of drugs used to treat cough - expectorants to increase mucus secretion and thinning, mucolytics to break up thick mucus, and antitussives/cough suppressants to reduce cough reflex. Antihistamines work by blocking the H1 receptor and antagonizing the effects of the chemical histamine, which is involved in allergic responses. First and second generation antihistamines are used to treat allergic diseases by reducing symptoms like itching, as well as other conditions involving histamine release such as

2. Cough:
Protective reflex caused by stimulation of sensory nerves
in the mucosa of pharynx, larynx, trachea, bronchi induced
by infections, stimulus like smoke, dust etc.
 Productive : Associated with sputum.
 Nonproductive : Dry cough-No sputum.
Purpose : To expel respiratory secretions.

3. 1. Pharyngeal Demulcents :
Glycerine and liquorice.
Drugs used for cough:
2. Expectorants (Bronchial secretion enhancers ) :
Sodium citrate, potassium citrate, potassium iodide,
Guaiphenesin, vasaka, ammonium chloride

4. 4. Antitussives (cough suppressants) :
Codeine, pholcodeine, noscapine, dextromethorphan
3. Mucolytic :
Bromhexine, Ambroxol,
Acetylcysteine, carbocisteine.

5. Expectorants
Increase the tracheobronchial gland secretions,
Reduce the viscosity,
Facilitating the removal of sputum.
Used in chronic productive cough

6. Mucolytics
 Break thick tenacious sputum
 Lower sputum viscosity
Induce thin copious secretion
 sputum comes out easily with less effort
 Used in productive cough in chronic bronchitis

7. Antitussives/ Cough suppressants
 In brain - raise the threshold of cough center,
 ↓cough reflex, suppress cough center in medulla.
 In respiratory tract - reduces the tussal impulses.
 Used in Dry unproductive cough, cough in allergic states
 Severe productive cough – disturb sleep, in hernia/ piles/
cardiac disease/ocular surgery

8. Histamine :
A chemical present in mast cells, skin, gastric,
intestinal mucosa, lungs etc.

10. Antihistaminic drugs block H1 receptor and antagonize
the actions of histamine.

11. Classification
A) First generation antihistamines :
Diphenhydramine, Dimenhydrinate,
Hydroxyzine, Promethazine.
Pheniramine, Cyprohyptadine, Cinnarizine,
Meclizine, Buclizine, Chlopheniramine,
Dimethindene, Tripolidine, Clemastine, Cyclizine

12. A) Second generation antihistamines :
Cetirizine, Levocetrizine, Azelastine, Mizolastine,
Loratadine, Desloratadine, Rupatadine, Fexophenadine.
Advantages of 2nd
generation:
Higher H1 selectivity
No anticholinergic side effects
Don’t cross BBB – no CNS depressant
Don’t impair psychomotor performance in driving
Additional anti-allergic mechanism - ↓↓ histamine release

13. Limitations of 2nd
generation:
Relatively expensive
No anticholinergic – rhinorrhea in cold
No sedation – in severe cough, in child

14. Uses of antihistamines
1.Allergic diseases :
Block the effects of released histamines (pruritus,
urticaria, dermatitis, rhinitis, conjunctivitis) by allergens,
blood transfusion, saline infusion reaction (chills, rigor),
anaphylaxis
2. Insect bite, ivy poisoning and abnormal dermographism
3. Skin: Allergy, Pruritides, urticaria, atopic dermatitis

15. 4. Allergic rhinitis
5. Common cold
6. Cough
7. Seasonal asthma
8.Parkinsonism

16. 9. Vomiting :
Motion sickness, Morning sickness, Postoperative,
Radiation & drug induced vomiting.
10. Vertigo
11.Preanesthetic medication

17. Adverse effects of antihistaminics:
CNS - Sedation, diminished alertness and concentration,
motor incoordination.
Anti Chol - Dry mouth, blurring vision, constipation,
urinary retention.
Topical application – contact dermatitis.