Cetirizine
H1 antihistamines
H1 antihistamines
A second-generation antihistamine for hay fever and hives; it acts fast and is the most likely of its group to cause some drowsiness.
Quick facts
- Group
- H1 antihistamines
- Target
- Histamine H1 receptor
- Used for
- Allergic rhinitis · Urticaria
- Key effects
- Drowsiness and tiredness · Dry mouth · Headache
- Monitor
- Symptom relief · Drowsiness
- ATC
- R06AE07
No doses: the clinician sets them by the current guideline.
Mechanism of action
The figure shows desloratadine bound to the human histamine H1 receptor (cryo-electron microscopy); cetirizine binds the same site.
Cetirizine is the carboxylic-acid metabolite of hydroxyzine. As a selective peripheral H1 inverse agonist it blocks histamine effects on nerves, vessels and glands of the nose, eyes and skin. It penetrates the brain more than loratadine or fexofenadine, which explains why a minority of patients feel drowsy.
- Cetirizine binds peripheral H1 receptors
- The receptors stay in their inactive form
- Histamine itch, sneezing and wheals are blocked
- A little enters the brain: some people feel drowsy
Indications
- Allergic rhinitis Allergic rhinitis →
- Urticaria (hives) Urticaria and angioedema →
- Itch of allergic skin conditions such as atopic eczema Atopic dermatitis →
Adverse effects
Common
- Drowsiness and tiredness
- Dry mouth
- Headache
- Sore throat
Contraindications
- Hypersensitivity to cetirizine, levocetirizine or hydroxyzine
- Caution and lower exposure in kidney disease
Key interactions
- Alcohol, benzodiazepines, opioids and other CNS depressants
- Additive sedation and slowed breathing
What is monitored
- Symptom relief
- Drowsiness
- Kidney function in older adults
Administration and safety
- Oral tablets, chewable tablets or syrup; with or without food
- Eye-drop and injectable forms exist in some countries
- Levocetirizine is its active enantiomer, not a different drug: they are not combined
Pregnancy and breastfeeding
Cetirizine has a large body of pregnancy experience without a clear signal of harm; use is decided with the clinician.
Nursing care
- Teach not to drive or operate machinery until the effect is known, and to avoid alcohol
- Check kidney function in older or renally impaired patients
- Ask about previous reactions to hydroxyzine (cross-sensitivity)
Pharmacokinetics
- Absorption
- Rapidly absorbed by mouth
- Metabolism
- Very little metabolism
- Elimination
- Mostly unchanged in the urine, so it builds up in kidney failure
- Onset and duration
- Within about an hour, lasting about a day
Test yourself
Think of the answer, then tap the question to see it.
Which first-generation antihistamine is cetirizine derived from?
Hydroxyzine; cetirizine is its metabolite.
Among second-generation antihistamines, which is most likely to cause drowsiness?
Cetirizine.
Why does cetirizine accumulate in kidney failure?
It is excreted largely unchanged in the urine.
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: Cetirizine: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); Cetirizine: antihistamine that relieves allergy symptoms - NHS (NHS, 2026); DailyMed - HYDROXYZINE HYDROCHLORIDE tablet, film coated (DailyMed (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.