Cetirizine
A second-generation antihistamine, a metabolite of hydroxyzine, for hay fever, year-round allergic rhinitis and chronic hives.
Drug card
- How it works
- Blocking peripheral H1 receptors while largely staying out of the brain
- Used for
- Seasonal and year-round allergic rhinitis
- Chronic hives (chronic idiopathic urticaria)
- Known for
- Drowsiness
- Its name
- -izine means a piperazine H1 antihistamine (cyclizine type)
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does cetirizine work?
A human metabolite of hydroxyzine that selectively blocks peripheral H1 receptors and shows no measurable binding to other receptors. Little enters the brain, so sedation is mild, and it also limits the late-phase arrival of eosinophils in allergic skin and eyes. It is excreted mainly by the kidneys.
Like other second-generation antihistamines: Second-generation antihistamines selectively block peripheral H1 receptors, so histamine can no longer make small vessels leak and swell or trigger itching, sneezing and a runny nose. They pass poorly into the brain and have little affinity for other receptors, so at usual doses they cause little drowsiness and almost no anticholinergic effect, and one dose lasts about a day.
Uses
What is cetirizine used for?
- Seasonal and year-round allergic rhinitis
- Chronic hives (chronic idiopathic urticaria)
Side effects
Side effects of cetirizine
- DrowsinessKnown for
- Tiredness
- Headache
- Dizziness
- Dry mouth
- Abdominal pain and nausea
- Agitation; rarely aggression or hallucinations
- Difficulty passing urine (rare)
- Liver function changes or hepatitis (rare)Serious
- Seizures (rare)Serious
- Intense itching or hives after stopping
- Anaphylaxis (very rare)Serious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Mainly cleared by the kidneys: lower doses in kidney impairment; contraindicated in end-stage kidney disease.
- Allergy to hydroxyzine or other piperazine drugs is a contraindication.
- Alcohol and other CNS depressants can add to drowsiness in sensitive people.
- Care in epilepsy and in conditions that predispose to urinary retention.
Good to know: Drowsiness is its commonest side effect (about 10% vs 5% on placebo in trials), a larger excess than reported for loratadine or fexofenadine.
Remember it
A way to remember it
The second generation stays out of your head.
Newer antihistamines barely cross the blood-brain barrier and ignore muscarinic receptors, so they ease allergy with little drowsiness or dry mouth; cetirizine is the one most likely to make people sleepy.
Written for biofideX
Its name
-izine means piperazine H1 antihistamine (cyclizine type)
Cetirizine, hydroxyzine and cyclizine share it; cetirizine is a metabolite of hydroxyzine. Promethazine, a phenothiazine antihistamine, ends in -azine instead.
- Every drug name stem
Its class
Second-generation antihistamines
Other second-generation antihistamines with a card:
Easily mixed up with first-generation antihistamines, H2 receptor antagonists and leukotriene receptor antagonists.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Cetirizine hydrochloride oral solution: label (DailyMed)
- Cetirizine tablets: SmPC (emc)
- Cetirizine (NCI Thesaurus)
- Cetirizine (NHS)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Lungs and allergy
Cetirizine is one of 16 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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