ZYRTEC
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ZYRTEC (ZYRTEC).
Selective histamine H1-receptor antagonist; inhibits histamine release from mast cells and basophils.
| Metabolism | Hepatic via CYP3A4 and CYP2D6 to inactive metabolites; minimal first-pass metabolism. |
| Excretion | Cetirizine is primarily excreted unchanged in urine (approximately 70% renal elimination) and feces (about 10%). |
| Half-life | Terminal elimination half-life is approximately 8-11 hours in healthy adults, prolonged in renal impairment (e.g., up to 20 hours in moderate renal failure). |
| Protein binding | 93% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | Volume of distribution is 0.5-0.8 L/kg, indicating distribution into total body water and extravascular tissues. |
| Bioavailability | Oral bioavailability is 70-85% (approximately 100% after correcting for renal excretion of absorbed dose). |
| Onset of Action | Oral: clinical effect (pruritus relief) within 1-2 hours; peak effect at 6-8 hours. |
| Duration of Action | Duration of action for antihistamine effect is approximately 24 hours, supporting once-daily dosing. Suppression of histamine-induced wheal and flare persists beyond 24 hours. |
| Molecular Weight | 388.9 |
| Action Class | H1 Antihistaminics (second Generation) |
| Brand Substitutes | Cetrilix 5mg Syrup, Cetmac 5mg/5ml Syrup, Ralcet 5mg/5ml Syrup, Mast 1 Syrup, Ezin Syrup, Elgnil 10mg Tablet, Dio 1 10mg Tablet, Citrazan 10mg Tablet, Cetrizine Tablet, Cetcip Tablet |
5-10 mg orally once daily; maximum 10 mg/day.
| Dosage form | SOLUTION |
| Renal impairment | CrCl 11-31 mL/min: 5 mg orally once daily; CrCl <11 mL/min or hemodialysis: 5 mg orally every other day. |
| Liver impairment | No adjustment required for mild to moderate impairment; not studied in severe impairment. |
| Pediatric use | 6-11 months: 2.5 mg orally once daily; 12-23 months: 2.5 mg orally once daily; 2-5 years: 2.5-5 mg orally once daily; 6-11 years: 5-10 mg orally once daily. |
| Geriatric use | Initiate at 5 mg orally once daily; monitor for sedation and dizziness; no specific dose adjustment based on age alone. |
| 1st trimester | Generally considered safe; no increased risk of major malformations in human studies. Limited data; avoid unnecessary use. |
| 2nd trimester | No known harm; minimal systemic exposure expected. Avoid excessive doses. |
| 3rd trimester | No known harm; minimal systemic exposure. Not associated with neonatal adverse effects. |
Clinical note
Comprehensive clinical and safety monograph for ZYRTEC (ZYRTEC).
| Placental transfer | Cetirizine crosses the placenta; cord blood concentrations are approximately 25-50% of maternal plasma concentrations. Limited data; no evidence of fetal harm. |
| Breastfeeding | Cetirizine is excreted into breast milk in low concentrations (estimated infant dose <4% of maternal weight-adjusted dose). No adverse effects reported in infants. Caution in preterm or neonates due to immature drug elimination. Monitor for drowsiness or irritability. |
■ FDA Black Box Warning
None.
| Serious Effects |
Hypersensitivity to cetirizine or any of its excipientsSevere renal impairment (CrCl <10 mL/min) for extended release formulations
| Precautions | Avoid use in patients with severe hepatic impairment, Use with caution in renal impairment (CrCl < 10 mL/min), May cause drowsiness; avoid driving or operating machinery |
| Food/Dietary | No significant food interactions. Take with or without food; food delays absorption slightly but does not affect overall bioavailability. Avoid concomitant grapefruit juice as it may reduce drug efficacy (weak interaction). |
| Clinical Pearls |
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| Lactation Rating | L2 (Safer) |
| Teratogenic Risk | Pregnancy Category B. Animal studies show no evidence of teratogenicity. In humans, first trimester exposure does not increase major malformations. Second and third trimester use is not associated with fetal harm. Caution in third trimester due to potential for uterine contractions (rare). |
| Fetal Monitoring | No specific monitoring required. Observe for maternal sedation or anticholinergic effects. |
| Fertility Effects | No adverse effects on fertility in animal studies. In humans, no known impact on male or female fertility. |
| Cetirizine is a second-generation antihistamine with minimal anticholinergic effects; it is less sedating than first-generation antihistamines but more sedating than loratadine or fexofenadine. Onset of action is within 1 hour. Renal dose adjustment is required (CrCl <31 mL/min: 5 mg daily). Avoid in patients with galactose intolerance, Lapp lactase deficiency, or glucose-galactose malabsorption due to lactose content. |
| Patient Advice | Take the medication exactly as prescribed; do not exceed the recommended dose. · May cause drowsiness; avoid driving or operating heavy machinery until you know how you react. · Avoid alcohol and other CNS depressants as they may increase drowsiness. · Use caution in elderly patients due to increased risk of dizziness and falls. · Report any signs of allergic reaction (rash, itching, swelling) to your healthcare provider. · Store at room temperature away from moisture and heat. |