diphenhydramine hydrochloride: clinical use

Prescribing considerations

• Confirm the indication and formulation.
• Assess cumulative sedative and antimuscarinic burden, including pharmacy-bought sleep, allergy, cough and cold products.
• Use particular caution in older people; avoid oral use in older patients with confusion.
• Assess persistent sleep disturbance for an underlying cause.
• Consider lactose content when relevant to the selected oral tablet.

Contraindications and cautions

• Oral: hypersensitivity to diphenhydramine or an excipient, stenosing peptic ulcer or pyloroduodenal obstruction.
• Cream: sensitivity to antihistamines or benzoates; application to mucous membranes, eczematous conditions, extensively broken or denuded skin, or acute vesicular or exudative dermatoses.
• Do not combine the cream with another diphenhydramine-containing product.

Monitoring

• Sedation, cognition, psychomotor impairment, unsteadiness and falls risk.
• Antimuscarinic effects, particularly blurred vision, urinary retention and worsening narrow-angle glaucoma.
• Paradoxical excitation or confusion, especially in older people.
• Local burning, rash, eczema or photosensitivity with the cream.
• Infant drowsiness, irritability and feeding during oral use while breastfeeding.

Clinical pharmacology

An ethanolamine-derived H1-receptor antagonist with marked sedative and antimuscarinic effects. Oral diphenhydramine is rapidly absorbed and undergoes substantial first-pass metabolism. Absorption through largely intact skin is minimal.

Formulation and product differences

• Oral tablets have systemic antihistamine, sedative and antimuscarinic effects and are selected here for temporary sleep disturbance.
• Cream acts locally on allergic skin symptoms and has minimal systemic absorption through intact skin, but can cause sensitisation or photosensitivity.
• The selected oral tablet contains lactose; check the individual product's excipients.

Tablet

Route: Oral

Strengths: 25 mg, 50 mg