Second-generation H1 antihistamine (piperazine)
Cetirizine is a second-generation antihistamine used to relieve the symptoms of respiratory allergies (allergic rhinitis) and urticaria: sneezing, runny and itchy nose, watery eyes and itching. It is less sedating than older antihistamines and can therefore be taken during the day.
Also known as: Zyrtec, cetirizina, cetirizine, Zirtin
Cetirizine + ritonavir: possible increased cetirizine exposure.
Cetirizine is predominantly eliminated renally, with minimal hepatic metabolism, so the pharmacokinetic interaction with ritonavir is limited; the clinical risk is additive sedation — the cetirizine label warns about drowsiness and the increased effect with alcohol, sedatives and tranquillisers, and ritonavir also causes fatigue and CNS symptoms. In patients with renal or hepatic impairment (in whom cetirizine accumulates and the dose should be reduced — the label recommends asking a doctor) and in the elderly, the combination requires vigilance: monitor drowsiness, dizziness and driving ability, and use the lowest effective cetirizine dose.
Cetirizine + ritonavir: additive risk of sedation/drowsiness. Monitor, especially with renal or hepatic impairment.
Ritonavir may raise cetirizine concentrations (pharmacokinetic interaction described in the label).
Sedative effects and tolerance to therapy.
Marked drowsiness, dry mouth, confusion.
Watch for excessive drowsiness and antihistamine adverse effects.
DailyMed (FDA) — approved Cetirizine label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=b92d959d-dd35-b2a3-e053-2995a90af3ff ; approved Ritonavir label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=d2f8c6ba-5e06-4b03-8ca5-b4fd7e5a8925 — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Food does not significantly alter cetirizine absorption.
May take with or without food.
EMC-UK (MHRA) — approved Cetirizine SmPC: https://www.medicines.org.uk/emc/product/3217/smpc
Alcohol may potentiate cetirizine-induced drowsiness.
Limit alcohol, especially when driving or operating machinery.
EMC-UK (MHRA) — approved Cetirizine SmPC: https://www.medicines.org.uk/emc/product/3217/smpc
Cetirizine is renally excreted; in severe impairment the dose must be reduced.
Reduce the dose (e.g. 5 mg/day) in severe renal impairment.
EMC-UK (MHRA) — approved Cetirizine SmPC: https://www.medicines.org.uk/emc/product/3217/smpc
Cetirizine is one of the preferred antihistamines in pregnancy; available studies show no teratogenicity.
Can be used in all trimesters when indicated, at the lowest effective dose.
Excreted into breast milk in small amounts; compatible with breastfeeding.
No specific additional contraception.
EMC-UK (MHRA) — approved Cetirizine SmPC: https://www.medicines.org.uk/emc/product/3217/smpc
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Second-generation H1 antihistamine (active metabolite of hydroxyzine) with minimal CNS penetration — less sedation and anticholinergic effects than first-generation H1 antihistamines; onset ~1 h and duration ≥24 h with once-daily dosing.
Selective peripheral antagonist of histamine H1 receptors, blocking the allergic response (vasodilation, increased capillary permeability, pruritus, sneezing) without significant cholinergic or serotonergic antagonism.
Well absorbed orally; plasma peak ~1 h; ~93% protein binding; absorption is not relevantly affected by food; Tmax ~0.5-1 h.
Minimal hepatic metabolism (cetirizine is largely excreted unchanged); no relevant additional active metabolite; predominantly renal excretion (~60-70% unchanged) and faecal.
Elimination half-life ~8.3 h (146 healthy volunteers); prolonged in renal impairment and the elderly (adjust the dose); half-life ~6 h in children 6-12 years.
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
