cetirizine
Second-generation antihistamine· Brands: Zyrtec, Reactine, AllertekPO
Mechanism of action
Cetirizine is a selective peripheral H1 receptor antagonist. It blocks histamine binding at H1 receptors, preventing the allergic response. It has a low affinity for central nervous system H1 receptors, leading to reduced sedation compared with first-generation antihistamines. It also inhibits the release of mediators from mast cells and basophils, though its primary action is via H1 blockade.
Pharmacokinetics
Cetirizine is rapidly and extensively absorbed after oral administration, with peak plasma concentrations occurring within about 1 hour. Bioavailability is approximately 70% and is not affected by food. It has a plasma half-life of around 8 to 10 hours. It is minimally metabolised in the liver, and the majority of the dose is excreted unchanged in the urine. In patients with renal impairment, doses may need adjustment. It crosses the placenta and is present in breast milk.
Indications & dosing
Allergic rhinitis (seasonal and perennial)
For adults and adolescents 12 years and over. Reduce dose in renal impairment.
- adult · PO: 10 mg once daily · For adults and adolescents 12 years and over. Reduce dose in renal impairment.
Allergic rhinitis (seasonal and perennial)
Child 1-2 years. Reduce dose in renal impairment.
- pediatric · PO: 2.5 mg twice daily · Child 1-2 years. Reduce dose in renal impairment.
Allergic rhinitis (seasonal and perennial)
Child 2-6 years: 2.5 mg twice daily or 5 mg once daily. Reduce dose in renal impairment.
- pediatric · PO: 2.5–5 mg once or twice daily · Child 2-6 years: 2.5 mg twice daily or 5 mg once daily. Reduce dose in renal impairment.
Allergic rhinitis (seasonal and perennial)
Child 6-12 years: 5 mg twice daily or 10 mg once daily. Reduce dose in renal impairment.
- pediatric · PO: 5–10 mg once or twice daily · Child 6-12 years: 5 mg twice daily or 10 mg once daily. Reduce dose in renal impairment.
Chronic urticaria
For adults and adolescents 12 years and over. Reduce dose in renal impairment.
- adult · PO: 10 mg once daily · For adults and adolescents 12 years and over. Reduce dose in renal impairment.
Chronic urticaria
Child 1-2 years. Reduce dose in renal impairment.
- pediatric · PO: 2.5 mg twice daily · Child 1-2 years. Reduce dose in renal impairment.
Chronic urticaria
Child 2-6 years: 2.5 mg twice daily or 5 mg once daily. Reduce dose in renal impairment.
- pediatric · PO: 2.5–5 mg once or twice daily · Child 2-6 years: 2.5 mg twice daily or 5 mg once daily. Reduce dose in renal impairment.
Chronic urticaria
Child 6-12 years: 5 mg twice daily or 10 mg once daily. Reduce dose in renal impairment.
- pediatric · PO: 5–10 mg once or twice daily · Child 6-12 years: 5 mg twice daily or 10 mg once daily. Reduce dose in renal impairment.
Contraindications & precautions
- Hypersensitivity to cetirizine, hydroxyzine, or piperazine derivatives · Cross-sensitivity between these agents may occur.
- Severe renal impairment (creatinine clearance <10 mL/min) · Clearance is reduced; alternative antihistamine may be needed.
- Patients on haemodialysis · Not recommended because of poor clearance.
- Reduce dose in moderate renal impairment (creatinine clearance 10-49 mL/min) and in hepatic impairment.
- Use with caution in patients with epilepsy or conditions that lower the seizure threshold.
- Caution in patients with urinary retention or a history of bladder outlet obstruction.
- Avoid concurrent use of alcohol or other central nervous system depressants.
- Caution in elderly patients, as they may be more susceptible to adverse effects.
- Caution during pregnancy and breastfeeding; weigh benefits against risks.
Adverse effects
- Somnolence
- Headache
- Dry mouth
- Fatigue
- Dizziness
- Nausea
- Angioedemaserious
- Anaphylaxisserious
- Severe skin reactions (e.g. Stevens-Johnson syndrome, toxic epidermal necrolysis)serious
- Hepatic dysfunctionserious
Renal & hepatic adjustment
- eGFR 30–50: Reduce dose to 5 mg once daily
- eGFR 10–29: Reduce dose to 5 mg every 48 hours
- eGFR 0–9: Reduce dose to 5 mg every 72 hours; use with caution
Monitoring, pregnancy & toxicity
- Clinical response to treatment (symptom relief) · On initiation and at follow-up
- Adverse effects: sedation, fatigue, dizziness, gastrointestinal disturbances · At each review
- Renal function (eGFR/CrCl) · At baseline and periodically in patients with renal impairment
- Pregnancy: Cetirizine is considered safe to use in pregnancy when clinically indicated. It is a second-generation antihistamine with a low risk of congenital malformations. Prefer it over first-generation antihistamines because it is less sedating. However, use continuously only if necessary.
- Toxicity: Sedation, drowsiness, dizziness, headache, dry mouth · Supportive care; monitor vital signs; administer activated charcoal if recent ingestion.
- Toxicity: Tachycardia, hypotension, and rare cardiac arrhythmias · Cardiac monitoring; treat arrhythmias per ACLS guidelines; obtain ECG.
- Toxicity: Agitation, irritability, or paradoxical excitation (more common in children) · Symptomatic; ensure safety; monitoring in a controlled environment.
Clinical notes
Cetirizine is indicated for allergic rhinitis, chronic idiopathic urticaria, and other allergic skin conditions. It is generally well tolerated, with the most common adverse effects being mild sedation, fatigue, and dry mouth. Children and elderly patients may experience paradoxical stimulation. Because it is excreted renally, use caution in renal impairment. Cetirizine is not to be confused with levocetirizine, its active enantiomer. It should be used with caution in patients predisposed to urinary retention or glaucoma. It has a lower sedative potential than first-generation antihistamines, but patients should be warned of possible drowsiness.
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BNF; local formulary