Introduction
Expectorants are medicines that help in removing thick or sticky mucus from the respiratory tract. They work either by increasing the volume of respiratory secretions or by decreasing the viscosity of mucus. By thinning and loosening the mucus, they make coughing more productive and help clear airways effectively.
Expectorants act mainly through two mechanisms: mucokinetic action (stimulating secretion and movement) or mucolytic action (breaking down mucus structure).
Mucokinetic Expectorants
These drugs stimulate bronchial secretions, increase the volume of respiratory tract fluid and improve ciliary movement. Some also act as gastric irritants to initiate reflex secretion of respiratory mucus.
Common Mucokinetic Expectorants
- Volatile oils – Anise oil, Eucalyptus oil
- Ammonium chloride
- Sodium citrate
- Guaiacol
- Guaifenesin
Mechanism and Key Points
- Volatile oils: Provide mild expectoration by stimulating bronchial secretory cells.
- Ammonium chloride: Acts as a gastric irritant, causing reflex increase in bronchial secretions. Large doses may lead to metabolic acidosis.
- Sodium citrate: Converts to bicarbonate inside the body, making mucus thinner in alkaline pH.
- Guaiacol and Guaifenesin: Safe and effective expectorants. Guaifenesin is less irritating and increases secretion from bronchial glands along with improving ciliary movement.
Typical Dose
Guaifenesin: 100–200 mg twice or three times daily.
Popular Preparations
- Grilinctus Syrup – Dextromethorphan + Chlorpheniramine + Guaifenesin + Ammonium chloride
- Benadryl – Diphenhydramine + Ammonium chloride + Sodium citrate + Menthol
- Zeet Expectorant – Diphenhydramine + Ammonium chloride + Guaifenesin + Bromhexine + Menthol
Mucolytic Expectorants
Mucolytics break down mucus structure, mainly by reducing the viscosity of secretions. They make mucus less sticky and easier to clear by ciliary movement or coughing.
Important Mucolytics
- Acetylcysteine
- Carbocisteine
- Bromhexine
- Ambroxol
- Dornase-alpha
Acetylcysteine
Decreases mucus viscosity by breaking disulfide (-S-S-) bonds in mucoproteins. Works best in slightly alkaline conditions (pH 7–9). Given via nebulisation, especially in cystic fibrosis and chronic bronchitis.
Adverse Effects
- Nausea, vomiting
- Stomatitis
- Bronchospasm
Carbocisteine
Structurally related to acetylcysteine but with a protected –SH group, so its mucolytic effect does not involve splitting disulfide bonds. Dose: 250–500 mg three times daily. Side effects are similar to acetylcysteine.
Bromhexine
Depolymerises mucopolysaccharides and increases lysosomal enzyme activity to break down mucus network. Dose: 8–16 mg three times daily.
Side Effects
- Gastric irritation
- Rhinorrhoea
Ambroxol
A metabolite of bromhexine with similar action. More effective when mucus plugs are present. Dose: 30 mg two to three times daily.
Dornase-Alpha
A recombinant human DNase enzyme. It reduces sputum viscosity by hydrolysing extracellular DNA released from dead neutrophils in cystic fibrosis. Dose: 2.5 mg once daily.
Common Preparations
- Acetylcysteine: Mucomix – 600 mg tablet; 200 mg/ml injection
- Carbocisteine: Mucodyne – 375 mg capsule; 250 mg/5 ml syrup; combinations like Carbomox
- Bromhexine: 8 mg tablet; 4 mg/5 ml syrup
- Ambroxol: 30 mg tablets; 30 mg/5 ml syrup; 7.5 mg/ml drops
Detailed Notes:
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