Acetylcysteine Mucolytic

Acetylcysteine is a mucolytic given orally or by nebuliser to thin viscous airway secretions in chronic bronchitis, COPD and other chronic respiratory conditions with sputum retention. Evidence is modest, with a small reduction in exacerbations in chronic bronchitis and COPD at higher doses. Doses here apply to mucolytic use only and must not be used for paracetamol poisoning.

Classification. Mucolytic, thiol antioxidant.

Mechanism. The free thiol group breaks disulphide bonds in mucin, reducing mucus viscosity. It also replenishes glutathione and has antioxidant effects.

Pharmacokinetics. Oral bioavailability low (about 10%) from first-pass metabolism. Half-life about 6 hours. Renal excretion of metabolites.

Alternative, chronic bronchitis and COPD with thick sputum, adults and adolescents over 14 years. 200 mg three times daily or 600 mg once daily orally. For frequent exacerbations, 600 mg twice daily is used by specialists.

Children. Under 2 years: not advised. 2 to 5 years: 100 mg two or three times daily. 6 to 14 years: 200 mg twice daily.

Nebulised, adults. 3 to 5 mL of the 20% solution (600 to 1000 mg) two to three times daily, with a bronchodilator given first in patients with asthma or reactive airways.

First-line, emergency. Not used for mucolytic purposes.

Titration and loading. No loading dose. Reduce to the lowest effective dose once secretions ease.

Contraindications. Hypersensitivity. Caution in peptic ulcer disease, asthma (bronchospasm with nebulised use) and histamine intolerance.

Serious adverse effects. Bronchospasm (nebulised), urticaria and angioedema, rare severe skin reactions.

Common adverse effects. Nausea, vomiting, diarrhoea, stomatitis, rhinorrhoea, sulphurous odour.

Interactions. Cough suppressants (secretions accumulate; avoid together). Activated charcoal reduces absorption. Nitroglycerin: vasodilatation and headache are increased. Carbamazepine: lower levels.

Common prescribing errors. Giving with a cough suppressant. Nebulising without a bronchodilator in asthma. Applying mucolytic doses to poisoning, or the reverse.

Special groups.

• Pregnancy: acceptable if needed. Breastfeeding: probably compatible.

• Older adults: no adjustment, but check sodium load in effervescent forms.

• Kidney impairment: no adjustment. Liver impairment: no adjustment.

• East Africa: effervescent tablets carry sodium, which matters in heart failure and hypertension. Cough over 2 weeks needs tuberculosis testing before a mucolytic is added.

Formulations. Effervescent tablets 200 mg and 600 mg, granules, syrup, nebuliser solution 10% and 20%.

Administration. Dissolve effervescent tablets in a glass of water and drink straight away. Maintain good fluid intake.

Baseline. Sputum volume and viscosity, asthma history, history of peptic ulcer.

Monitoring. Sputum, exacerbation frequency, wheeze after nebulisation, gastrointestinal tolerance.

Stop and reduce rules. Stop for bronchospasm, rash or angioedema. Stop if no benefit after 4 weeks. Therapeutic drug monitoring is not used.

Referral and escalation. Refer for haemoptysis, recurrent exacerbations or suspected bronchiectasis or tuberculosis.