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Sedating H1 antihistamine Pregnancy: Contraindicated in pregnancy and breast-feeding. Clinical data in humans are inadequate to establish safety in early pregnancy and animal studies have shown reproductive toxicity; hydroxyzine crosses the placenta, which may give higher foetal than maternal concentrations. Sedating antihistamines in the latter part of the third trimester may cause neonatal irritability, paradoxical excitability and tremor, and hypotonia, movement/extrapyramidal disorders, clonic movements, CNS depression, neonatal hypoxic conditions or urinary retention have been observed after late pregnancy/labour exposure. Expected to be excreted into breast milk - should not be given to nursing mothers. (SPC 4.6 / 4.3)

Hydroxyzine hydrochloride

Brand names: Atarax, Ucerax

Hydroxyzine hydrochloride is a sedating first-generation (piperazine) antihistamine used in psychiatry for short-term anxiety and for pruritus, also exploiting its sedative properties.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Anxiety: 50-100 mg daily in divided doses. Pruritus: starting dose 25 mg at night, increasing as necessary to 25 mg three or four times daily
Route: Oral
Frequency: In divided doses; for pruritus up to three or four times daily
Max: 100 mg per day in adults and children over 40 kg in weight; 50 mg per day in the elderly
Should be used at the lowest effective dose and for the shortest possible duration; dosage should be adjusted according to the patient's response to therapy. Elderly: maximum daily dose 50 mg and a reduced dose is advised because of possible increased volume of distribution, prolonged action and age-related changes in hepatic metabolism and renal excretion; SPC 4.4 states hydroxyzine is not recommended in elderly patients. Hepatic impairment: reduce the total daily dose by 33%; avoid use in severe liver disease. eMC SPC section 4.2.

Paediatric dose

Route: Oral
Frequency: In divided doses
Max: Children up to 40 kg in weight: 2 mg/kg/day. Children and adolescents over 40 kg: 100 mg per day
The SPC states a per-kg MAXIMUM only, not a per-kg dose, so dosePerKg is left null. Age bands given in section 4.2: from 6 months to 6 years, 5-15 mg daily in divided doses adjusted depending on the child's weight; for children over 6 years, starting at 15-25 mg and increasing to 50-100 mg daily in divided doses adjusted according to the child's weight.

Dose adjustments

Renal

For patients with moderate or severe renal impairment it is recommended that the total daily dosage be reduced by 50% (SPC 4.2).

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Previous hypersensitivity to hydroxyzine hydrochloride, cetirizine, other piperazine derivatives, aminophylline or ethylenediamine, or any excipient
  • Known acquired or congenital QT interval prolongation
  • Known risk factor for QT prolongation - including known cardiovascular disease, significant electrolyte imbalance (hypokalaemia, hypomagnesaemia), family history of sudden cardiac death, significant bradycardia, or concomitant use of drugs known to prolong the QT interval and/or induce torsade de pointes
  • Asthmatics who have previously experienced a serious antihistamine-induced adverse bronchopulmonary effect
  • Porphyria
  • Pregnancy and breast-feeding
  • Contains lactose - avoid in rare hereditary galactose intolerance, Lapp lactase deficiency or glucose-galactose malabsorption

Side effects

  • CNS depression - drowsiness through to deep sleep, lassitude, dizziness and incoordination; sedation, somnolence and psychomotor impairment
  • Paradoxical stimulation, especially at high doses and in children and the elderly; agitation, confusion, hallucinations, sleep disturbance
  • Antimuscarinic effects - dry mouth, constipation, blurred vision/accommodation disorder, urinary retention
  • QT interval prolongation and ventricular arrhythmias including torsade de pointes; tachycardia, palpitation, hypotension
  • Headache, tremor, convulsions, extrapyramidal effects, ataxia
  • Hypersensitivity reactions, anaphylaxis, angioedema; very rare severe skin reactions (AGEP, toxic epidermal necrolysis, Stevens-Johnson syndrome, erythema multiforme)

Interactions

  • Drugs known to prolong the QT interval and/or induce torsade de pointes - concomitant use is a contraindication (SPC 4.3)
  • Caution with antimuscarinic burden - hydroxyzine has potential antimuscarinic actions (angle-closure glaucoma, urinary retention, prostatic hyperplasia, pyloroduodenal obstruction, decreased GI motility) (SPC 4.4)

Clinical monograph

How it works

It antagonises central and peripheral histamine H1 receptors, producing sedative, anxiolytic and antipruritic effects, with additional antimuscarinic activity.

Prescribing in practice

  • Hydroxyzine prolongs the QT interval and is contraindicated where there is known prolongation or significant risk factors, so avoid in cardiac risk, use the lowest effective dose for the shortest time, and avoid other QT-prolonging drugs.
  • Its antimuscarinic and sedative effects warrant caution in the elderly, in urinary retention, glaucoma and prostatic enlargement.
  • It potentiates alcohol and other central nervous system depressants and can impair driving and skilled tasks.

Monitoring

Monitor for excessive sedation, antimuscarinic effects and, where cardiac risk exists, QT-related concerns, with attention to the elderly.

Counselling the patient

  • Expect drowsiness and avoid driving or operating machinery if affected.
  • Avoid alcohol while taking this medicine.
  • Report palpitations or fainting, and use only for the short term as advised.

Evidence & guidelines

MHRA guidance restricting hydroxyzine to the lowest effective dose and shortest duration reflects its recognised risk of QT prolongation.

Reference: MHRA Drug Safety Update; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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