Antitussives and Codeine Overview

Antitussives (Cough Suppressants)

• Drugs work by suppressing the cough center in the medulla (both central and peripheral effects).
• Opioids (codeine, pholcodeine, noscapine, dextromethorphan) are the most effective for cough suppression.

Codeine

• Codeine is a prodrug, metabolized to morphine.
• Found in opium poppy plants.
• Has less addictive potential compared to other opioids.
• Depresses the respiratory center.
• Effective for cough suppression at low doses (less than 15 mg).
• Side effects include drowsiness, thickened phlegm, and constipation.

Noscapine & Pholcodeine

• Related to papaverine.
• Do not cause addiction, pain relief, or constipation.
• Do not interfere with the movement of mucus.
• Available as a syrup (15 mg noscapine and 10 mg pholcodeine).

Dextromethorphan

• Available in syrup, tablets, and spray forms.
• Mechanism of action (MOA): NMDA receptor antagonist.
• Used to suppress coughs caused by minor throat or bronchial irritation (often accompanying flu or colds).
• Can also provide some pain relief.
• Potential side effects include nausea, dizziness, blurred vision, vomiting, and drowsiness.

Expectorants

• Act peripherally to increase bronchial secretions or decrease mucus viscosity.
• This facilitates removal of mucus by coughing.

Classification of Expectorants

• Directly acting: Guaifenesin (glyceryl guaiacolate), sodium and potassium citrate or acetate. These act directly to increase bronchial secretions via salt action.
  • Guaifenesin increases the volume of secretions and reduces viscosity for easier removal.
• Reflexly acting: Ammonium salts. These irritate the stomach, triggering a reflex that increases bronchial secretions and sweating.

Mucolytics

• Help in expectoration by liquefying viscous tracheobronchial secretions.
• Examples include bromhexine and acetylcysteine.

Bromhexine

• MOA: Thinning and fragmentation of mucopolysaccharide fibers.
• Result: Increased volume and reduced viscosity of sputum.

Acetylcysteine

• MOA: Opens disulfide bonds in sputum mucoproteins to reduce viscosity.
• Used directly into the respiratory tract.
• Quickly reduces sputum viscosity, often used for cystic fibrosis.
• Potential side effects include nausea, vomiting, and bronchospasm (especially in those with asthma).

Antihistamines

• Often added to antitussive and expectorant formulations.
• Offer sedation and anticholinergic effects, relieving cough but affecting cough center secretions.
• Not selective for cough center.
• Used for allergic coughs, but not asthma.
• Examples include chlorpheniramine, promethazine, and diphenhydramine

Bronchodilators

• Beta2 agonists (salbutamol, terbutaline) are examples.
• MOA: Increase the surface velocity of airflow during coughing, enabling better clearance of airway secretions.
• Not used routinely for all cough types, but only when bronchoconstriction is present.

Pharyngeal Demulcents

• Soothe the throat, (directly and by promoting salivation).
• Decrease afferent impulses from inflamed/irritated pharyngeal mucosa
• Provide relief for dry coughs from throat irritation.
• Examples include lozenges, cough drops, glycerine, licorice, honey.

Specific Treatment Approach to Cough

• Etiology: Identifying the cause of the cough (e.g., infections, smoking, chronic bronchitis, pulmonary issues, asthma, sinusitis).
• Treatment: Corresponding treatment approach (e.g., antibiotics for infections, smoking cessation, inhaled medications for asthma)

This quiz explores antitussives, focusing on cough suppressants like codeine, noscapine, pholcodeine, and dextromethorphan. Learn about their mechanisms, effectiveness, side effects, and how they work to suppress coughs. Test your knowledge on the different opioid and non-opioid options available.