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Sedating antihistamine (phenothiazine) Pregnancy: Avoid in 3rd trimester — neonatal extrapyramidal symptoms, withdrawal. Earlier pregnancy: weigh risks; loratadine/cetirizine preferred for allergy.

Alimemazine tartrate

Brand names: Vallergan

Adult dose

Dose: Pruritus / urticaria: 10 mg BD–TDS, increased to 100 mg/day if severe. Premedication: 25–50 mg 1–2 hours before procedure.
Route: Oral
Frequency: Two to three times daily for pruritus
Max: 100 mg/day for pruritus
Heavy sedation — counsel about driving and skilled tasks. Avoid in elderly (falls, confusion).

Paediatric dose

Route: Oral
Frequency: Variable by indication
Pruritus / urticaria: 2–5 yrs 2.5 mg TDS–QDS; 6–12 yrs 5 mg TDS–QDS. Sedation pre-op: 1–2 mg/kg 1–2 hours before procedure (max 50 mg). NOT for children under 2 years (sedation, sudden death risk). BNFc.

Clinical pearls

  • Useful for severe pruritus refractory to non-sedating antihistamines — sedation is part of the therapeutic effect.
  • Heavy sedation persists into the next day — patients should not drive or operate machinery the morning after a night-time dose.
  • Avoid in elderly (BEERS criteria) — high falls and confusion risk.
  • NOT recommended as a routine bedtime sedative for children — only specific specialist scenarios.
  • Phenothiazine structure means weak antipsychotic activity at high doses — but not licensed for psychosis.

Contraindications

  • Children under 2 years (CNS depression, sudden infant death)
  • Severe hepatic impairment
  • Comatose states / severe CNS depression
  • MAOIs within 14 days
  • Phaeochromocytoma
  • Bone marrow depression

Side effects

  • Marked drowsiness, dizziness
  • Anticholinergic: dry mouth, blurred vision, urinary retention, constipation
  • Postural hypotension
  • Extrapyramidal symptoms at high doses (phenothiazine class effect)
  • QT prolongation (caution with other QT drugs)
  • Photosensitivity, contact dermatitis (handling)
  • Cholestatic jaundice (rare)

Interactions

  • CNS depressants (alcohol, opioids, benzodiazepines): additive sedation
  • MAOIs: hypertensive crisis, hyperpyrexia — avoid
  • Anticholinergics: additive effects
  • QT-prolonging drugs (amiodarone, citalopram, methadone): additive QT risk
  • Levodopa: antagonised by phenothiazines

Monitoring

  • ECG if used long-term or with QT-prolonging drugs

Reference: BNFc; BNF 90; BNF for Children 2024; SmPC Vallergan; MHRA Drug Safety Update on sedating antihistamines in children. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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