diphenhydramine hydrochloride + guaifenesin + levomenthol: clinical use

Prescribing considerations

• Confirm that the cough is suitable for symptomatic self-care; review persistent, worsening or recurrent symptoms.
• Assess sedative and antimuscarinic burden, alcohol intake and risks of falls, confusion, urinary retention or angle-closure glaucoma.
• Seek clinical review for asthma, chronic or smoking-related cough, chronic bronchitis, emphysema or excessive secretions.
• Use caution in moderate-to-severe renal dysfunction or hepatic disease.
• Consider glucose, sucrose, ethanol, sodium, benzoate and colouring content when relevant.
• Guaifenesin metabolites may interfere with urinary 5-HIAA and VMA testing.

Contraindications and cautions

• Hypersensitivity to any active ingredient or excipient
• Current monoamine oxidase inhibitor treatment or use within the previous 14 days
• Children younger than 12 years

Monitoring

• Drowsiness, psychomotor impairment and paradoxical excitation
• Antimuscarinic effects, including blurred vision, dry mouth, constipation and urinary retention
• Palpitations, tachycardia, confusion, hallucinations or seizures
• Progression of cough and associated respiratory symptoms
• Infant alertness and feeding if used during breastfeeding

Clinical pharmacology

Diphenhydramine is a centrally acting antitussive with H1-antihistamine, antimuscarinic and sedative activity. Guaifenesin reduces sputum viscosity. Levomenthol has mild local anaesthetic and decongestant properties.

Formulation and product differences

• The preparation is a clear red oral syrup.
• It contains glucose and sucrose, relevant to diabetes and specified hereditary sugar-intolerance disorders.
• It contains ethanol, sodium, sodium benzoate and Ponceau 4R; the colouring may cause allergic reactions.