Second-generation antihistamine (H1 antagonist) Pregnancy: Prospectively collected data do not suggest maternal or foetal/embryonic toxicity above background rates; animal studies show no harmful effects. Caution should be exercised when prescribing to pregnant women. Cetirizine passes into breast milk (25-90% of plasma concentrations) — a risk of side effects in breastfed infants cannot be excluded; caution in lactating women.

Cetirizine

Brand names: Zirtek, Benadryl Allergy

Cetirizine is an oral second-generation antihistamine used for allergic rhinitis, allergic conjunctivitis and chronic urticaria.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 10 mg (1 tablet)

Route: oral

Frequency: once daily

Adults and adolescents over 12 years: 10 mg once daily; if drowsiness occurs the tablet can be taken in the evening. Duration of treatment varies with symptoms. Elderly: no dose reduction needed provided renal function is normal. PAEDIATRIC (UK SPC): the tablet formulation should not be used in children under 6 years (does not allow dose adjustment) — use a paediatric formulation; children 6-12 years 5 mg twice daily (half a tablet twice daily); adolescents over 12 years 10 mg once daily.

Dose adjustments

Renal

Adjust dosing interval by renal function. Normal (eGFR >=90) and mildly decreased (60-90): 10 mg once daily. Moderately decreased (30-60): 5 mg once daily. Severely decreased (15-30, not on dialysis): 5 mg once every 2 days. End-stage renal disease (<15) requiring dialysis: contraindicated. In patients with combined hepatic and renal impairment, adjust dose as for renal impairment.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance, to any of the excipients, to hydroxyzine or to any piperazine derivatives
End-stage renal disease with eGFR below 15 ml/min

Side effects

Somnolence
Fatigue
Dizziness
Headache
Dry mouth

Interactions

No clinically significant interactions expected (pharmacokinetic/pharmacodynamic/tolerance profile)
No significant interaction reported with pseudoephedrine or theophylline (400 mg/day)
Alcohol / other CNS depressants — concurrent use may cause additional reductions in alertness and impairment of performance in sensitive patients (cetirizine does not potentiate alcohol at 0.5 g/L)

Clinical monograph

How it works

It is a selective peripheral histamine H1-receptor antagonist that blocks histamine-mediated allergic symptoms with relatively little central nervous system penetration.

Prescribing in practice

Although classed as non-sedating, cetirizine causes drowsiness in some people, who should avoid driving or skilled tasks until they know how it affects them, and additive sedation with alcohol or CNS depressants should be avoided.
The dose should be reduced in renal impairment because it is largely eliminated unchanged by the kidneys.
Onset of relief is rapid, making it suitable for both regular and as-needed use in allergic rhinitis.

Monitoring

No routine monitoring is required; review symptom control and any sedation, with dose adjustment in significant renal impairment.

Counselling the patient

Find out how it affects you before driving, as it can cause drowsiness in some people.
Avoid alcohol if it makes you sleepy.
It can be taken regularly or as needed for allergy symptoms.

Evidence & guidelines

Second-generation antihistamines such as cetirizine are recommended first-line for allergic rhinitis and chronic urticaria in NICE and allergy guidelines.

Reference: BSACI Urticaria Guidelines; ARIA Guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways