diphenhydramine hydrochloride + paracetamol: clinical use

Prescribing considerations

• Confirm that pain is disturbing sleep; this product is not licensed for insomnia alone.
• Review total paracetamol exposure and concurrent oral or topical antihistamines.
• Assess sedative and anticholinergic burden, falls risk and the need to drive or operate machinery.
• Use particular caution with hepatic or renal impairment, alcohol-related liver disease, malnutrition, sepsis or other glutathione-depleted states.
• Older people are more susceptible to confusion, paradoxical excitation and other adverse effects.

Contraindications and cautions

• Hypersensitivity to paracetamol, diphenhydramine or an excipient
• Porphyria
• Avoid in older patients with confusion; use caution with narrow-angle glaucoma, prostatic enlargement or urinary retention, seizure disorders, myasthenia gravis, asthma, bronchitis or COPD.
• Use caution with monoamine oxidase inhibitors, including recent use, and other sedative or antimuscarinic medicines.

Monitoring

• Review persistent or recurrent bedtime pain and persistent headache rather than continuing self-treatment.
• Monitor for sedation, cognitive impairment, dizziness, falls and antimuscarinic adverse effects.
• In patients with relevant risk factors, remain alert to unexplained high-anion-gap metabolic acidosis, particularly with prolonged paracetamol exposure or concurrent flucloxacillin.
• Any suspected overdose requires urgent assessment even when early symptoms are absent.

Clinical pharmacology

Paracetamol is an analgesic and antipyretic with mainly central activity. Diphenhydramine is an ethanolamine H1-receptor antagonist with sedative, antimuscarinic and local-anaesthetic properties; it also inhibits CYP2D6.

Formulation and product differences

• The selected product is a white to off-white, capsule-shaped oral tablet marked “PM” on one side.
• It is supplied in child-resistant blister packs; pack sizes may vary.