Expectorants

Expectorants are drugs intended to increase the volume or hydration of airway secretions and ease their clearance. Guaifenesin is the main oral agent. Evidence for oral expectorants is weak, and evidence is stronger for nebulised hypertonic saline and mannitol in selected conditions.

Classification. Guaifenesin, potassium iodide, ammonium chloride and ipecacuanha (oral); nebulised hypertonic saline; inhaled dry powder mannitol.

Mechanism. Oral expectorants may stimulate gastric vagal reflexes to raise respiratory tract fluid, though this is unproven. Hypertonic saline and mannitol draw water into the airway lumen by osmosis, hydrate mucus and improve mucociliary clearance.

Pharmacokinetics. Guaifenesin is absorbed rapidly with a half life of about 1 hour and is cleared by hepatic oxidation. Iodide is concentrated in the thyroid and salivary glands.

Guaifenesin. 200 to 400 mg orally every 4 hours, maximum 2400 mg in 24 hours. Sustained release 600 to 1200 mg every 12 hours.

Hypertonic saline. 7 percent nebulised, 4 mL twice daily in cystic fibrosis and non-cystic fibrosis bronchiectasis, taken after a bronchodilator. Strength of 3 percent is used when 7 percent is not tolerated.

Mannitol. Dry powder 400 mg twice daily in cystic fibrosis and bronchiectasis, after a tolerance test.

Potassium iodide. Obsolete in most practice because of thyroid toxicity.

Ammonium chloride. Gastric irritation and acidosis limit use.

Differences. Only hypertonic saline and mannitol have evidence for sputum clearance and fewer exacerbations in bronchiectasis and cystic fibrosis.

Acute cough and bronchitis. Expectorants are not needed, and antibiotics are not indicated for uncomplicated acute bronchitis.

Bronchiectasis and cystic fibrosis. Airway clearance physiotherapy, hydration and hypertonic saline. Give salbutamol before hypertonic saline, and supervise the first dose with FEV1 measurement.

Chronic bronchitis. Limited benefit from guaifenesin. Use only if the patient reports easier sputum clearance.

Adjuncts. Hydration and humidification help airway clearance.

Adverse effects. Guaifenesin causes nausea, vomiting, dizziness and rash. Hypertonic saline and mannitol cause cough, bronchospasm and sore throat. Iodide causes hypothyroidism or hyperthyroidism, goitre, rash, acne and salivary gland swelling. Ammonium chloride causes gastric irritation and metabolic acidosis.

Contraindications. Iodide in thyroid disease and pregnancy. Ammonium chloride in hepatic and renal impairment. Mannitol in mannitol-induced bronchospasm.

Interactions. Few with guaifenesin. Iodide interacts with lithium, antithyroid drugs and potassium-sparing diuretics.

Monitoring. Sputum volume and ease, FEV1 after hypertonic saline, and thyroid function with prolonged iodide.

Special groups. Pregnancy: avoid iodide because of foetal goitre, and avoid guaifenesin in the first trimester. Breastfeeding: avoid iodide. Children: oral expectorants are not advised under 6 years. Older adults: watch for sedation if combined with other drugs. Hepatic and renal impairment: avoid ammonium chloride.

Referral and escalation. Sputum that is purulent with fever, haemoptysis, weight loss or persistent cough over 2 weeks needs infection and tuberculosis assessment. Bronchospasm with hypertonic saline needs stopping the drug.