dextromethorphan hydrobromide + diphenhydramine hydrochloride + levomenthol: clinical use

Prescribing considerations

• Confirm that the cough is dry rather than productive; assess persistent cough, asthma, emphysema, chronic bronchitis or excessive secretions.
• Review serotonergic medicines, CYP2D6 inhibitors, sedatives, alcohol use and duplicate cough or antihistamine products.
• Consider susceptibility to sedation, antimuscarinic effects, dependence and misuse.
• Use caution with hepatic dysfunction or moderate-to-severe renal impairment.
• Account for glucose, sucrose, ethanol, Ponceau 4R, benzyl alcohol, sodium benzoate, propylene glycol and sodium in the syrup.

Contraindications and cautions

• Hypersensitivity to an active ingredient or excipient
• Current MAOI use or use within the previous 14 days
• Concurrent SSRI treatment
• Respiratory failure or risk of respiratory failure
• Age under 12 years

Monitoring

• Sedation, cognition, coordination and driving safety
• Respiratory status and thickening of secretions
• Antimuscarinic effects, particularly urinary retention and angle-closure symptoms
• Features of serotonin syndrome
• Escalating use, dependence or withdrawal symptoms

Clinical pharmacology

Dextromethorphan is a centrally acting non-opioid antitussive extensively metabolised through CYP2D6. Diphenhydramine is a centrally penetrant H1 antihistamine with antitussive, sedative and antimuscarinic activity. Levomenthol provides cooling sensory effects with mild local anaesthetic and decongestant properties. Combination pharmacodynamic studies are unavailable.

Formulation and product differences

• The product is a clear red oral syrup that may darken towards brown with age.
• It contains sugars and excipients relevant to intolerance, diabetes, allergy and hepatic or renal impairment.
• It contains ethanol and should remain in its original container; follow the pack’s after-opening storage instructions.