Guaifenesin

Guaifenesin is an oral expectorant given to loosen bronchial secretions in acute respiratory infection. Evidence of benefit is weak and inconsistent.

Classification. Expectorant.

Mechanism. Thought to increase airway fluid volume and reduce mucus viscosity, possibly through a vagally mediated gastric reflex.

Pharmacokinetics. Well absorbed orally. Half-life about 1 hour. Hepatic metabolism to inactive metabolites, excreted in urine.

Alternative, productive cough from acute chest infection, adults and children from 12 years. Immediate-release 200 to 400 mg every 4 hours. Extended-release 600 to 1200 mg every 12 hours. Maximum 2400 mg daily.

Children 6 to 11 years. 100 to 200 mg every 4 hours. Maximum 1200 mg daily.

Children 4 to 5 years. 50 to 100 mg every 4 hours. Maximum 600 mg daily.

Under 4 years. Not advised.

Duration. Up to 7 days. Review if cough persists.

Emergency and specialist use. None. Loading and titration do not apply.

Contraindications. Hypersensitivity. Some combination products contain porphyria-provoking or sympathomimetic ingredients.

Serious adverse effects. Rare hypersensitivity. Kidney stones have been reported with very high doses over long periods.

Common adverse effects. Nausea, vomiting, dizziness, headache, rash.

Interactions. No important drug interactions. It can interfere with urinary tests for vanillylmandelic acid and 5-hydroxyindoleacetic acid, causing false positive results.

Common prescribing errors. Duplicating guaifenesin in several combination cold products. Combining with a cough suppressant.

Special groups.

• Pregnancy: limited data; avoid in the first trimester. Breastfeeding: probably compatible.

• Older adults: no adjustment.

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

• East Africa: widely sold in combination cough syrups. Cough lasting over 2 weeks, with weight loss or night sweats, needs tuberculosis testing.

Formulations. Syrup, tablets 200 mg, 400 mg, 600 mg and 1200 mg extended-release, combination products.

Administration. Take with a full glass of water. Swallow extended-release tablets whole.

Baseline. Cough duration and red flag features.

Monitoring. Cough and sputum, review at 7 days.

Stop and reduce rules. Stop if there is no benefit at 7 days. Therapeutic drug monitoring is not used.

Referral and escalation. Refer for fever over 3 days, haemoptysis, breathlessness or cough over 2 weeks.