dextromethorphan hydrobromide + paracetamol + promethazine: clinical use

Prescribing considerations

• Confirm that all three active ingredients are required and avoid therapeutic duplication.
• Assess cough character and cause; chronic cough, respiratory disease or substantial secretions require clinical review.
• Review serotonergic, sedating, anticholinergic, CYP2D6-inhibiting and QT-prolonging products.
• Consider confusion, falls, urinary retention, glaucoma and paradoxical excitation, particularly in older people.
• Assess substance-misuse history because dextromethorphan misuse, dependence and withdrawal have been reported.
• Promethazine can interfere with immunological urine pregnancy tests.

Contraindications and cautions

• Hypersensitivity to an active ingredient or excipient.
• Existing or threatened respiratory failure.
• Current or recent MAOI treatment.
• The selected oral solution additionally lists hepatic or renal impairment, concurrent SSRI treatment and age under 12.
• Respect formulation-specific age and excipient restrictions, including hereditary fructose intolerance with maltitol-containing solution and specified lactose disorders with capsules.

Monitoring

• Monitor clinically relevant sedation, confusion, anticholinergic effects, respiratory depression and serotonin toxicity.
• Consider hepatic risk after excess exposure or with liver disease, harmful alcohol use, malnutrition or glutathione depletion.
• With paracetamol and flucloxacillin, investigate unexplained high-anion-gap metabolic acidosis in susceptible patients.
• Monitor for exaggerated or prolonged dextromethorphan effects with CYP2D6 inhibition or suspected poor-metaboliser status.

Clinical pharmacology

Paracetamol is an analgesic and antipyretic cleared mainly after hepatic conjugation. Promethazine is a sedating phenothiazine H1-antihistamine with anticholinergic activity. Dextromethorphan is a centrally acting antitussive extensively metabolised through CYP2D6 to dextrorphan, with important interindividual variability.

Formulation and product differences

• Selected products include capsules and a sugar-free, mint-flavoured oral solution.
• The solution contains ethanol, propylene glycol and maltitol, is supplied with a measuring cup and should be shaken before use.
• Capsules contain lactose and have a higher licensed minimum age than the selected solution.
• Contraindications and cautions differ between formulations; check the product-specific information.