Hydroxyzine
H1 antihistamines
H1 antihistaminesPregnancy: contraindicated
Hydroxyzine is contraindicated in early pregnancy because animal studies showed fetal abnormalities and human data are inadequate.
A sedating antihistamine used for itch, anxiety and sedation before surgery; it can prolong the QT interval.
Quick facts
- Group
- H1 antihistamines
- Target
- Histamine H1 receptor
- Used for
- Anxiety and tension · Sedation before
- Key effects
- Drowsiness and slowed reactions · Dry mouth
- Monitor
- ECG in patients with heart disease · Skin
- ATC
- N05BB01
No doses: the clinician sets them by the current guideline.
Mechanism of action
The figure shows doxepin, a tricyclic first-generation H1 blocker, in the human H1 receptor; hydroxyzine binds the same site.
Hydroxyzine is a piperazine first-generation H1 inverse agonist. It suppresses histamine-driven itch and wheals and, by entering the brain, calms anxiety and causes sedation without being a benzodiazepine. It is converted in the liver to cetirizine. It can block cardiac potassium channels and prolong the QT interval, especially with other QT-prolonging drugs.
- Hydroxyzine blocks H1 receptors in the skin: less itch
- It enters the brain: calm and sedation
- The liver turns it into cetirizine, also active
- Cardiac potassium-channel block can lengthen the QT
Indications
- Itch from allergic skin conditions such as urticaria and atopic dermatitis Urticaria and angioedema →
- Anxiety and tension (short term) Generalized anxiety disorder →
- Sedation before and after general anaesthesia
Adverse effects
Common
- Drowsiness and slowed reactions
- Dry mouth, blurred vision and constipation
- Urinary retention, especially with an enlarged prostate
- Dizziness and poor coordination
Contraindications
- Prolonged QT interval
- Early pregnancy
- Hypersensitivity to hydroxyzine, cetirizine or levocetirizine
Key interactions
- Other drugs known to prolong the QT interval
- Additive QT prolongation and risk of torsades de pointes
- Alcohol, benzodiazepines, opioids and other CNS depressants
- Additive sedation and slowed breathing
- Other anticholinergic drugs (tricyclic antidepressants, oxybutynin, antipsychotics)
- Additive dry mouth, urinary retention, constipation and confusion
What is monitored
- ECG in patients with heart disease, low potassium or magnesium, or other QT drugs
- Sedation and fall risk
- Skin: stop at the first sign of a pustular rash
Administration and safety
- Oral tablets, capsules or syrup; intramuscular injection exists (deep muscle, never intravenous, subcutaneous or intra-arterial)
- Its salts (hydrochloride, pamoate) are the same drug: not combined
Pregnancy and breastfeeding
Hydroxyzine is contraindicated in early pregnancy because animal studies showed fetal abnormalities and human data are inadequate.
Nursing care
- Check the ECG and electrolytes when there are QT risk factors
- Assess sedation and help with walking
- Ask about pregnancy before starting
- Teach not to drive or operate machinery until the effect is known, and to avoid alcohol
Pharmacokinetics
- Absorption
- Rapidly absorbed by mouth
- Metabolism
- Liver, partly to cetirizine
- Elimination
- Urine and faeces as metabolites
- Onset and duration
- Calming and antipruritic effect within an hour
Test yourself
Think of the answer, then tap the question to see it.
Which ECG finding is a contraindication to hydroxyzine?
A prolonged QT interval.
Which second-generation antihistamine is a metabolite of hydroxyzine?
Cetirizine.
What are three uses of hydroxyzine?
Allergic itch, short-term anxiety and sedation around surgery.
Connections
← Back to the class: H1 antihistamines
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - HYDROXYZINE HYDROCHLORIDE tablet, film coated (DailyMed (U.S. National Library of Medicine), 2026); Hydroxyzine: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.