CETIRIZINE HYDROCHLORIDE ALLERGY
Clinical safety rating: safe
No significant drug interactions at recommended doses May cause somnolence although less than first-generation antihistamines.
Cetirizine hydrochloride is a second-generation histamine H1-receptor antagonist. It acts by selectively and reversibly blocking histamine H1 receptors on effector cells (e.g., smooth muscle, endothelial cells, mucous glands), thereby inhibiting histamine-mediated allergic responses such as vasodilation, increased vascular permeability, bronchoconstriction, and itching. It does not prevent histamine release but antagonizes its effects.
| Metabolism | Cetirizine is a carboxylated metabolite of hydroxyzine and undergoes minimal hepatic metabolism. Approximately 60% of a dose is excreted unchanged in urine via glomerular filtration and active tubular secretion. The remaining fraction is metabolized in the liver by oxidative O-dealkylation mediated by CYP3A4, forming inactive metabolites. A small portion (about 10%) is metabolized via other pathways including glucuronidation. |
| Excretion | Renal: approximately 70% (60% as unchanged drug, 10% as metabolites); Fecal: approximately 10%; Biliary: negligible |
| Half-life | Terminal elimination half-life: approximately 8-11 hours in healthy adults; increases to ~18-20 hours in elderly (due to decreased renal function); prolonged in renal impairment (CrCl <31 mL/min: up to 20-30 hours) |
| Protein binding | Approximately 93% bound to plasma proteins (primarily albumin) |
| Volume of Distribution | 0.3-0.5 L/kg (approximately 30-50 L in adults), indicating distribution into total body water |
| Bioavailability | Oral: approximately 70% (bioequivalent for tablet, capsule, and syrup formulations) |
| Onset of Action | Oral: 1-2 hours for symptom relief; 2-4 hours for peak effect |
| Duration of Action | 24 hours (supports once-daily dosing); antihistamine effects persist for at least 24 hours |
| Molecular Weight | 461.82 |
| Action Class | Second-generation antihistamine |
5-10 mg orally once daily; maximum 10 mg/day.
| Dosage form | TABLET |
| Renal impairment | GFR 10-30 mL/min: 5 mg once daily. GFR <10 mL/min or on dialysis: contraindicated. |
| Liver impairment | Child-Pugh A: no adjustment. Child-Pugh B or C: 5 mg once daily. |
| Pediatric use | 6-12 months: 2.5 mg once daily. 12 months-2 years: 2.5 mg twice daily. 2-6 years: 2.5 mg twice daily or 5 mg once daily. 6-12 years: 5-10 mg once daily. Weight-based: 0.25 mg/kg twice daily (if <6 years). |
| Geriatric use | Initiate 5 mg once daily; increase to 10 mg if needed based on renal function; monitor for CNS effects. |
| 1st trimester | Generally considered safe; no increased risk of major malformations in human studies. |
| 2nd trimester | No evidence of fetal harm; used when benefit outweighs risk. |
| 3rd trimester | Avoid near term due to potential for withdrawal symptoms or respiratory depression in neonates. |
Clinical note
No significant drug interactions at recommended doses May cause somnolence although less than first-generation antihistamines.
| FDA category | Animal |
| Placental transfer | Cetirizine crosses the placenta; fetal concentrations are similar to maternal plasma. |
| Breastfeeding | Cetirizine is excreted into breast milk in low amounts; unlikely to cause adverse effects in infants. Monitor for drowsiness or irritability. |
■ FDA Black Box Warning
None
| Common Effects | urticaria |
| Serious Effects | Anaphylaxis, Angioedema, Severe hypotension, Seizures, Hepatotoxicity, Thrombocytopenia |
Severe renal impairment (CrCl <10 mL/min)Known hypersensitivity to cetirizine or any excipient
| Precautions | Renal impairment: Dose adjustment required for creatinine clearance < 31 mL/min or in end-stage renal disease (not recommended for hemodialysis patients)., Hepatic impairment: No dose adjustment in mild-to-moderate hepatic impairment; caution in severe hepatic disease., CNS depression: May cause drowsiness, fatigue, or dizziness; caution when driving or operating heavy machinery., Urinary retention: Use with caution in patients with predisposing factors (e.g., bladder neck obstruction, prostatic hyperplasia)., Elderly patients: Increased risk of sedation and dizziness; monitor for falls., Pregnancy: Category B; use only if clearly needed., Lactation: Excreted in breast milk; avoid use in nursing mothers. |
Loading safety data…
| Lactation Rating | L2 (Probably Compatible) |
| Teratogenic Risk | FDA Pregnancy Category B. First trimester: no evidence of teratogenicity in animal studies; limited human data show no increased risk of major malformations. Second and third trimesters: no known fetal risks; however, use only if clearly needed. |
| Fetal Monitoring | No specific maternal-fetal monitoring required. Clinical monitoring for maternal adverse effects (e.g., sedation, dry mouth) and fetal growth if used chronically. |
| Fertility Effects | No evidence of impaired fertility in animal studies. Human data insufficient; theoretical possibility of anticholinergic effects on cervical mucus, but unlikely at clinical doses. |
| Food/Dietary |
| No significant food interactions. Grapefruit juice not known to interact. |
| Clinical Pearls | Onset of action within 1 hour; duration ~24 hours. Minimal anticholinergic effects. Dose adjust in renal impairment (CrCl <30 mL/min: 5 mg daily). Can cause drowsiness in some patients. Not recommended in pregnancy unless benefit outweighs risk. |
| Patient Advice | Take once daily with or without food. · Avoid alcohol or other CNS depressants. · May cause drowsiness; use caution when driving. · Do not exceed recommended dose. · Store at room temperature, protect from light. |