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Sedating antihistamine (phenothiazine)

Alimemazine tartrate

Brand names: Vallergan

Alimemazine is a sedating phenothiazine antihistamine, used for short-term symptomatic relief of urticaria and pruritus and as a premedication, and historically for sedation.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

It blocks histamine H1 receptors, with additional antimuscarinic and central depressant actions that account for its sedative effect.

Prescribing in practice

  • Avoid in young children and use with particular caution given the risk of paradoxical excitation and respiratory depression; it is not recommended for sedation in very young infants.
  • Sedation may be marked and additive with alcohol and other CNS depressants.
  • Use cautiously in the elderly and in those with prostatic hypertrophy, glaucoma or hepatic impairment owing to antimuscarinic and sedative effects.

Monitoring

Routine laboratory monitoring is not generally required; review for excessive sedation, antimuscarinic effects and continued need.

Counselling the patient

  • This medicine can make you drowsy; do not drive or operate machinery if affected.
  • Avoid alcohol while taking it.
  • Seek advice before giving to children.

Evidence & guidelines

Use is guided by the SPC and longstanding clinical practice rather than large modern trials.

Reference: SmPC Vallergan; MHRA Drug Safety Update on sedating antihistamines in children; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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