ZYRTEC ALLERGY
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ZYRTEC ALLERGY (ZYRTEC ALLERGY).
Selective peripheral histamine H1-receptor antagonist; inhibits histamine release from mast cells and basophils.
| Metabolism | Primarily metabolized by CYP3A4 to its active metabolite cetirizine; also undergoes some metabolism by CYP2D6. |
| Excretion | Renal excretion of unchanged drug accounts for approximately 70% of elimination; approximately 10% is excreted in feces via biliary route. Total renal excretion includes both parent drug and metabolites, with cetirizine largely unchanged. |
| Half-life | Terminal elimination half-life is approximately 8.3 hours (range 6–10 hours) in healthy adults, prolonged to 20–25 hours in patients with renal impairment (CrCl < 40 mL/min). No significant difference in elderly vs. young adults with normal renal function. |
| Protein binding | Approximately 93% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | Volume of distribution is approximately 0.3–0.4 L/kg, indicating distribution primarily into extracellular fluid and limited tissue penetration. |
| Bioavailability | Oral bioavailability is approximately 100% (well absorbed); no significant first-pass metabolism. Bioavailability is unaffected by food. |
| Onset of Action | Oral: Onset of antihistaminic effect occurs within 1 hour; peak effect at approximately 4–6 hours. Symptom relief may begin as early as 20–30 minutes in some individuals. |
| Duration of Action | Duration of action is approximately 24 hours, supporting once-daily dosing. Clinical effect persists for at least 24 hours after a single dose, with sustained suppression of histamine-induced wheal-and-flare response. |
| Molecular Weight | 461.84 |
5–10 mg orally once daily; maximum dose 10 mg/day.
| Dosage form | TABLET, ORALLY DISINTEGRATING |
| Renal impairment | CrCl 30–49 mL/min: 5 mg once daily; CrCl 10–29 mL/min: 5 mg every other day; CrCl <10 mL/min or hemodialysis: contraindicated. |
| Liver impairment | Child-Pugh Class A: no adjustment; Class B or C: 5 mg once daily. |
| Pediatric use | 6–12 years: 5–10 mg once daily; 2–5 years: 2.5 mg once daily; 6–23 months: 2.5 mg once daily (off-label but commonly used). |
| Geriatric use | Initiate at 5 mg once daily; increase to 10 mg if response insufficient, considering increased susceptibility to sedation. |
| 1st trimester | Generally considered safe; no increased risk of major malformations in human studies. |
| 2nd trimester | No known fetal risk; preferred antihistamine during pregnancy. |
| 3rd trimester | Use with caution near term; may cause irritability or sedation in neonate. |
Clinical note
Comprehensive clinical and safety monograph for ZYRTEC ALLERGY (ZYRTEC ALLERGY).
| Placental transfer | Crosses placenta; low levels in fetal circulation relative to maternal plasma. |
| Breastfeeding | Cetirizine is excreted into breast milk in low concentrations; considered compatible with breastfeeding. Monitor infant for drowsiness. |
| Lactation Rating |
■ FDA Black Box Warning
None
| Common Effects | Sleepiness Fatigue Vomiting Dryness in mouth Headache Constipation |
| Serious Effects |
Hypersensitivity to cetirizine or any componentSevere renal impairment (CrCl <10 mL/min)
| Precautions | Use with caution in patients with hepatic or renal impairment, May cause CNS depression; avoid concurrent use with alcohol or other CNS depressants |
| Food/Dietary | No significant food interactions. Alcohol may increase CNS depression and drowsiness; avoid or limit alcohol consumption. |
Loading safety data…
| L2 (Probably Compatible) |
| Teratogenic Risk | FDA Pregnancy Category B. No evidence of teratogenicity in animal studies; inadequate human studies. First trimester: minimal risk based on limited data; no increased major malformations. Second and third trimesters: no known fetal harm; use only if clearly needed. |
| Fetal Monitoring | No specific monitoring required. Routine prenatal care. Observe for maternal sedation, especially when used with other CNS depressants. |
| Fertility Effects | No significant effects on fertility reported in animal studies. Human data limited; no known adverse impact on male or female fertility. |
| Clinical Pearls | Zyrtec Allergy (cetirizine) is a second-generation antihistamine with faster onset (1 hour) and longer duration (24 hours) than first-generation agents. It is renally eliminated, so dose adjustment is required in renal impairment (CrCl <30 mL/min: 5 mg daily). It does not cause significant sedation at recommended doses but may cause drowsiness in some patients. Avoid concurrent use with CNS depressants. |
| Patient Advice | Take one 10 mg tablet once daily with or without food. · Do not exceed the recommended dose; taking more does not improve allergy relief and increases side effects. · Avoid driving or operating heavy machinery until you know how this medication affects you, as it may cause drowsiness in some people. · If you have kidney problems, consult your doctor for dose adjustment. · Inform your doctor if you are pregnant, planning to become pregnant, or breastfeeding. · Store at room temperature away from moisture and heat. · Do not use if you have liver disease without doctor approval. |