Cetirizine
Cetirizine is a second-generation H1 antihistamine used in adults and children for allergic rhinitis, conjunctivitis and chronic urticaria. It blocks peripheral H1 histamine receptors with limited central penetration and modest sedation.
- Chemical formula
- C21H25ClN2O3
- CAS number
- 83881-51-0
- ATC code
- R06AE07
- Molecular weight
- 388.89 g/mol
- Drug class
- Second-generation H1 antihistamine
- Also known as
- UCB 25991, Cetirizina
What is it?
Cetirizine is the active metabolite of hydroxyzine and was approved in the early 1990s. It is supplied as oral tablets, oral solution and orodispersible tablets and is dispensed both with and without prescription depending on the market. Cetirizine has a more favourable safety profile than first-generation antihistamines, with limited blood-brain barrier penetration and reduced anticholinergic effects, although mild sedation can still occur in some patients.
Mechanism of action
Cetirizine selectively blocks peripheral H1 histamine receptors, antagonising the effects of histamine released by mast cells during allergic responses. The result is reduced vasodilation, decreased capillary permeability, suppression of pruritus and limitation of urticarial responses. The drug also has a small mast-cell stabilising effect at higher doses. Limited central nervous system penetration explains the lower incidence of sedation compared with classical antihistamines.
Pharmacokinetics
Cetirizine is rapidly absorbed orally, with peak plasma concentrations reached after one hour. Bioavailability is high. Plasma protein binding is approximately 93%. The drug is excreted predominantly unchanged in urine, with limited hepatic metabolism. The terminal half-life is approximately 8 to 10 hours, supporting once-daily dosing. Dose adjustment is required in moderate to severe renal impairment and in elderly patients with reduced renal function.
Indications
Cetirizine is approved in adults and children for the treatment of allergic rhinitis, including seasonal and perennial forms, allergic conjunctivitis and chronic idiopathic urticaria. According to international guidelines, it is one of the recommended second-generation antihistamines for first-line treatment of these conditions. Cetirizine is not the first-line treatment for severe asthma or anaphylaxis and is used cautiously in young children, with weight-based dosing.
Safety profile
Cetirizine is generally well tolerated. The most common adverse effects are mild somnolence, dry mouth, headache and gastrointestinal symptoms. Sedation is more common at higher doses than with loratadine or fexofenadine. Rare reports of severe pruritus on abrupt discontinuation after long-term use have been documented. According to the prescribing information, dose adjustment is needed in renal impairment and caution is required in the elderly.
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Frequently asked questions
Is cetirizine sedating? ▾
Cetirizine has a more favourable sedation profile than first-generation antihistamines such as diphenhydramine, but mild somnolence is still reported in some patients, particularly at higher doses or when combined with alcohol. According to the prescribing information, patients should be cautious about driving or operating machinery until they know how the medication affects them, especially during the first days of treatment.
Can cetirizine be taken every day? ▾
Yes. Cetirizine is approved for daily use in chronic allergic rhinitis and chronic urticaria. According to the prescribing information, daily dosing is well tolerated for prolonged periods. Periodic reassessment with the prescriber is still recommended, particularly when symptoms change or other treatments are added. Sudden discontinuation after very long-term use has been associated with rare cases of severe rebound pruritus.
Does cetirizine interact with other medications? ▾
Cetirizine has limited drug interactions because it is excreted predominantly unchanged in urine without major cytochrome P450 metabolism. Combination with alcohol or other CNS depressants may potentiate sedation. The combination with other antihistamines is generally avoided. According to the prescribing information, patients should disclose all concomitant medications and chronic conditions to the prescriber, especially renal disease.
Can children take cetirizine? ▾
Yes, in age- and weight-based dosing. Cetirizine is approved in children from age six months in some markets, with a graduated dose schedule defined in the prescribing information. Liquid formulations facilitate accurate dosing. According to clinical guidelines, paediatric prescribing should be discussed with a paediatrician or pharmacist, particularly in chronic conditions or in young children with renal impairment.
What are the main contraindications for cetirizine? ▾
Cetirizine is contraindicated in known hypersensitivity to the molecule, to hydroxyzine or to piperazine derivatives, and in severe renal impairment with creatinine clearance below the threshold defined in the prescribing information. Caution is required in the elderly, in epilepsy and during pregnancy and breastfeeding. According to the prescribing information, the medical history must be reviewed by a clinician before any prescription.
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