dextromethorphan hydrobromide + diphenhydramine hydrochloride: clinical use

Prescribing considerations

• Confirm that the cough is acute, dry and associated with a cold; the product is inappropriate for productive, chronic or asthma-related cough.
• Review serotonergic medicines, CYP2D6 inhibitors, sedatives and antimuscarinic burden.
• Consider susceptibility to sedation, confusion, falls, urinary retention and glaucoma, particularly in older or frail people.
• Assess substance misuse or mental health history because prolonged use can cause dependence and withdrawal.
• The solution contains sorbitol, maltitol, ethanol, sodium benzoate and flavourings; it is unsuitable in hereditary fructose intolerance.

Contraindications and cautions

• Hypersensitivity to an ingredient
• Current MAOI treatment or use within the previous two weeks
• Current SSRI treatment
• Respiratory failure or risk of respiratory failure
• Liver dysfunction
• Asthma-associated or productive cough
• Porphyria
• Age under 12 years

Monitoring

• Sedation, cognition and ability to drive safely
• Respiratory status where vulnerability exists
• Features of serotonin toxicity
• Urinary retention, blurred vision and acute glaucoma symptoms
• Escalating or prolonged use, dependence or withdrawal symptoms

Clinical pharmacology

Dextromethorphan is a centrally acting, non-opioid antitussive metabolised through CYP2D6 to active dextrorphan. Diphenhydramine is a CNS-penetrant H1 antagonist with sedative, antitussive, antiemetic and antimuscarinic activity.

Formulation and product differences

• The selected formulation is a brown, syrupy oral solution in an amber bottle.
• It contains ethanol, sorbitol, maltitol, sodium benzoate, glycerol, menthol, peppermint oil, anise oil, capsicum tincture, caramel and blackcurrant flavour.
• It is not described as sugar-free and is contraindicated in hereditary fructose intolerance.