Cough suppressants &
AIMST UNV, Malaysia.
Cough suppressants & Expectorants
• Cough is protective reflex, its purpose being expulsion of respiratory
secretions or foreign particles form the lungs and upper airway
• Cough may be useful (productive: sputum is coughed up/ drain the
airway) or useless (nonproductive/ dry)
• Useless cough should be suppressed
• Types of cough
– Classified based on duration, characters, quality and timing
• Acute : Sudden onset/ less than 3 weeks
• Sub-acute : 3-8 weeks
• Chronic : longer than eight weeks
Mechanism of cough
Stimulation of mechano-or chemoreceptors
(throat, respiratory passages or stretch
receptors in lungs)
Afferent impulses to cough center (medulla)
Efferent impulses via parasympathetic & motor
nerves to diaphragm, intercostal muscles & lung
Increased contraction of diaghramatic, abdominal
& intercostal (ribs) muscles noisy expiration
Drugs for cough
• Cough can be treated as a symptom (nonspecific therapy) or with
specific remedies (antibiotics, etc.)
• Nonspecific therapy
– Pharyngeal demulcents: Lozenges, cough drops, linctuses containing
syrup, glycerine, liquorice.
(a) Directly acting: Sodium and potassium citrate or acetate, potassium
iodide, guaiacol, guaiphenesin (glyceryl guaiacolate), balsum of tolu, vasaka and
(b) Mucolytics: Bromhexine, ambroxol, acetyl cysteine, carbocisteine.
(a) Antitussives (Cough center suppressants):
(a) Opioids: Codeine, pholcodeine, ethylmorphine, morphine.
(b) Nonopioids: Noscarpine, dextromethophan, oxeladin, chlorphedianol.
(c) Antihistamines: Chlorpheniramine, diphenhydramine, promethazine.
Demulcents and expectorants
• Expectorants: Increase the bronchial secretion or reduce its viscosity-
facilitating its removal by coughing.
• Sodium citrate or acetate (0.3- 1 g):
– Increase bronchial secretion by salt action.
• Potassium iodide (0.2- 0.3 g):
– Act directly on the bronchial secretory cells and are excreted into the
respiratory tract. It is an irritant and increase the volume of secretion.
– The irritant action is not desirable if bronchial mucosa is acutely inflamed.
– Dangerous in patients sensitive to iodine and interferes with thyroid function
– Prolonged use can induce goiter and hypothyroidism.
• Guaiacol ([Obtained form wood creosote]; 100-200 mg), tolu balsum (0.3-
0.6 g), Vasaka syrup (2-4 ml) and terpin hydrate (0.1-0.3 g)
– Directly increase bronchial secretion and mucosal ciliary action
– Gastric upset and rash can occur
Demulcents and expectorants
• Ammonium salts (o.3-1 g):
– Gastric irritants
– Reflexly enhance bronchial secretion and sweating
– Nauseating because of unpleasant taste
• Bromhexine/ Ambroxol:
– Derivative of the alkaloid vasicine obtained from Adhantoda vasica
– Potent mucolytic and mucokinetic, capable of inducing thin copious bronchial
– dissolving hard phlegm/ mucus plugs
– Side effect: Rhinorrhoea, lacrymation, gastric irritation, hypersensitivity.
– Derivatives of cysteine
– Reduce/ open the disulfide bridges in mucoproteins present in sputum.
– These drugs also act as antioxidants and may therefore reduce airway
– Side effects: Not popular one
• Opioids (Codeine/ pholcodeine):
– An opium alkaloid; less potent than morphine.
– Codeine, hydrocodone and hydromorphone are decrease sensitivity of central
cough center to peripheral stimuli and decrease mucosal secretions.
– Suppresses cough center (for 6 h).
– The antitussive action is blocked by naloxone.
– Abuse liability is low, but present; constipation is the chief drawnback.
– Higher doses respiratory depression and drowsiness can occur- driving may be
– Dose: adult 10-30 mg frequently used as syrup codeine phos. 4-8 ml.
– Similar in efficacy as antitussive to codeine.
– Long acting codeine (12 h); Dose: 10-15 g
– Similar to codeine; Dose: 10-15 mg.
• Noscapine (Narcotine):
– Opium alkaloid of benzoisoquinoline .
– It depresses cough but not narcotic, analgesic or dependence including
– Equipotent antitussive as codeine and useful in spasmodic cough.
– Side effect: Headache, nausea. It can produce bronchoconstriction by
stimulating histamine release.
– Synthetic compound; d-isomer has selective antitussive action; l-isomer has
– Effective as codeine, doesn't depress the mucociliary function of airway
– Antitussive effect is not blocked by naloxone
– Side effect: Dizziness, nausea, drowsiness, ataxia.
– Dose: 10-20 mg adult
• Oxeladin: Syn. centrally acting antitussive agent
• Bronchospasm and can induce or aggravate cough. Pulmonary
receptor stimulation can indcue both cough and
• Bronchodilators relieve cough and clear secretions by
increasing surface velocity of airflow during cough.
• H1 receptor antagonist have little effect on rhinitis associated
• Antihistamines reduce the parasympathetic tone of arterioles
and decrease secretion through their anticholinergic activity.
• Chlorpheniramine (2-5 mg), diphenhydramine (15-20 mg) and
promethazine (15-20 mg) are commonly used as a
• Second generation antihistamines like terfenadine, loratadine