Second-generation H1 antihistamine (active cetirizine enantiomer)
Levocetirizine 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 the active enantiomer of cetirizine, with less sedation.
Also known as: Xyzal, levocetirizina, levocetirizine
Levocetirizine + ritonavir: possible increased levocetirizine exposure.
Levocetirizine is predominantly eliminated renally (without significant hepatic metabolism), so the pharmacokinetic interaction with ritonavir is limited; the clinical risk is additive sedation — the levocetirizine 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 levocetirizine accumulates and the dose should be reduced) and in the elderly, the combination requires vigilance: monitor drowsiness, dizziness and driving ability, and use the lowest effective levocetirizine dose.
Levocetirizine + ritonavir: additive risk of sedation/drowsiness. Monitor, especially with renal or hepatic impairment.
Ritonavir may reduce levocetirizine clearance.
Sedative effects and tolerance.
Drowsiness, fatigue, dry mouth.
Watch for sedation and adverse effects.
DailyMed (FDA) — approved Levocetirizine label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1f722b84-08de-7e6a-41ac-2c9d9bb9fb43 ; 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)
Alcohol may potentiate drowsiness and impair psychomotor performance.
Avoid alcohol during treatment, especially when driving.
EMC-UK (MHRA) — approved Levocetirizine SmPC: https://www.medicines.org.uk/emc/product/9917/smpc
Levocetirizine is renally excreted; the dose must be adjusted.
Adjust the dose according to creatinine clearance.
EMC-UK (MHRA) — approved Levocetirizine SmPC: https://www.medicines.org.uk/emc/product/9917/smpc
Limited data in pregnancy; active cetirizine enantiomer.
Use only if benefit justifies risk; prefer cetirizine when available.
Limited data; prefer to avoid during breastfeeding.
No specific additional contraception.
EMC-UK (MHRA) — approved Levocetirizine SmPC: https://www.medicines.org.uk/emc/product/9917/smpc
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Active (R) enantiomer of cetirizine, a second-generation H1 antihistamine with twice the H1 receptor affinity and minimal sedation; predominantly renal excretion (~85.8% unchanged) — adjust in renal impairment.
Selective peripheral antagonist of histamine H1 receptors (the R enantiomer is responsible for the activity of racemic cetirizine), blocking the allergic response without relevant anticholinergic or serotonergic effects.
Good oral absorption with high bioavailability (no significant first-pass effect); plasma peak ~0.9 h; food slightly reduces Cmax (without changing AUC); protein binding ~92%.
Minimal hepatic metabolism (~14% — N-oxidation and O-dealkylation, with an inactive metabolite); predominantly renal excretion: 85.8% of the oral dose excreted unchanged within 48 h (equivalent to ~95% of the total dose eliminated); no relevant CYP interactions.
Half-life ~7-8 h (7.3-7.6 h in adults); prolonged in renal impairment and the elderly (CrCl <50 mL/min: reduced or alternate-day dosing).
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
