Cough suppressants &ExpectorantsDr. ParasuramanAIMST UNV, Malaysia.
Cough suppressants & Expectorants• Cough is protective reflex, its purpose being expulsion of respiratorysecretions or foreign particles form the lungs and upper airwaypassages .• Cough may be useful (productive: sputum is coughed up/ drain theairway) 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 coughStimulation of mechano-or chemoreceptors(throat, respiratory passages or stretchreceptors in lungs)Afferent impulses to cough center (medulla)Efferent impulses via parasympathetic & motornerves to diaphragm, intercostal muscles & lungIncreased contraction of diaghramatic, abdominal& intercostal (ribs) muscles noisy expiration(cough)
Drugs for cough• Cough can be treated as a symptom (nonspecific therapy) or withspecific remedies (antibiotics, etc.)• Nonspecific therapy– Pharyngeal demulcents: Lozenges, cough drops, linctuses containingsyrup, glycerine, liquorice.– Expectorants:(a) Directly acting: Sodium and potassium citrate or acetate, potassiumiodide, guaiacol, guaiphenesin (glyceryl guaiacolate), balsum of tolu, vasaka andterpin hydrate.(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 therespiratory 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 functiontest.– 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
Mucolytics• Bromhexine/ Ambroxol:– Derivative of the alkaloid vasicine obtained from Adhantoda vasica– Potent mucolytic and mucokinetic, capable of inducing thin copious bronchialsecretion– dissolving hard phlegm/ mucus plugs– Side effect: Rhinorrhoea, lacrymation, gastric irritation, hypersensitivity.• Acetylcysteine:– Derivatives of cysteine– Reduce/ open the disulfide bridges in mucoproteins present in sputum.– These drugs also act as antioxidants and may therefore reduce airwayinflammation.– Side effects: Not popular one
Antitussives• Opioids (Codeine/ pholcodeine):• Codeine:– An opium alkaloid; less potent than morphine.– Codeine, hydrocodone and hydromorphone are decrease sensitivity of centralcough 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 beimpaired.– Dose: adult 10-30 mg frequently used as syrup codeine phos. 4-8 ml.• Pholcodeine:– Similar in efficacy as antitussive to codeine.– Long acting codeine (12 h); Dose: 10-15 g• Ethylmorphine:– Similar to codeine; Dose: 10-15 mg.
Antitussives• Nonopioids:• Noscapine (Narcotine):– Opium alkaloid of benzoisoquinoline .– It depresses cough but not narcotic, analgesic or dependence includingproperties.– Equipotent antitussive as codeine and useful in spasmodic cough.– Side effect: Headache, nausea. It can produce bronchoconstriction bystimulating histamine release.• Dextromethorphan:– Synthetic compound; d-isomer has selective antitussive action; l-isomer hasanalgesic property.– Effective as codeine, doesnt depress the mucociliary function of airwaymucosa.– Antitussive effect is not blocked by naloxone– Side effect: Dizziness, nausea, drowsiness, ataxia.– Dose: 10-20 mg adult• Oxeladin: Syn. centrally acting antitussive agent
Bronchodilators• Bronchospasm and can induce or aggravate cough. Pulmonaryreceptor stimulation can indcue both cough andbronchoconstriction.• Bronchodilators relieve cough and clear secretions byincreasing surface velocity of airflow during cough.
Antihistamines• H1 receptor antagonist have little effect on rhinitis associatedwith colds.• Antihistamines reduce the parasympathetic tone of arteriolesand decrease secretion through their anticholinergic activity.• Chlorpheniramine (2-5 mg), diphenhydramine (15-20 mg) andpromethazine (15-20 mg) are commonly used as aantitussives.• Second generation antihistamines like terfenadine, loratadineare ineffective.