dextromethorphan hydrobromide + menthol: clinical use

Prescribing considerations

• Confirm that the cough is non-productive and assess persistent cough, red flags and underlying causes.
• Review serotonergic medicines, MAOIs and CYP2D6 inhibitors before supply.
• Consider sedation, misuse, dependence and withdrawal, particularly with prolonged use or a history of substance misuse or mental illness.
• Account for the syrup’s sucrose content in diabetes and hereditary disorders of sugar metabolism.

Contraindications and cautions

• Children under 12 years.
• Liver disease.
• Persistent or productive cough.
• Acute asthma attack, respiratory failure or risk of respiratory failure.
• Current or recent MAOI treatment.
• Hypersensitivity to dextromethorphan or menthol.
• Fructose intolerance, glucose-galactose malabsorption or sucrase-isomaltase insufficiency.

Monitoring

• Routine laboratory monitoring is not generally required for symptomatic use.
• Assess symptom persistence or deterioration and reconsider the cough’s cause.
• Monitor for excessive sedation, respiratory depression, serotonergic toxicity, misuse and dependence where relevant.

Clinical pharmacology

Dextromethorphan is absorbed orally and undergoes extensive hepatic first-pass metabolism, principally through genetically variable CYP2D6 O-demethylation to the active antitussive metabolite dextrorphan. Poor metabolisers and people taking CYP2D6 inhibitors may experience exaggerated or prolonged effects. Menthol acts locally to soothe irritation and perceived congestion.

Formulation and product differences

• The selected product is a sucrose-containing oral syrup rather than a sugar-free formulation.
• It contains a small amount of ethanol, sodium benzoate, peppermint oil, anise oil, capsicum tincture, cineole and other excipients.
• It is supplied in an amber glass bottle with a child-resistant closure and should be stored below 25°C.