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# Cetirizine (ctz)
## Overview
Second-generation, peripherally-selective H1-receptor antagonist. Rapid-acting, non-sedating (though dose-dependent somnolence can occur). Primarily renally eliminated.
## Primary Indications
- Seasonal/perennial allergic rhinitis
- Chronic idiopathic urticaria
## Adult Dosing
- **Usual:** 5–10 mg once daily
- **Maximum:** 10 mg/day
## Pediatric Dosing
Dosing varies by age and local protocols; verify product labeling.
- **6–12 months:** 2.5 mg once daily (if approved locally)
- **12 months – 6 years:** 2.5 mg twice daily **OR** 5 mg once daily
- **6–12 years:** 5–10 mg once daily
- **≥12 years:** same as adult
**Maximum pediatric daily dose:** 10 mg.
## Dose Adjustments
- **Renal impairment (CrCl <30 mL/min):** 5 mg once daily (adult/pediatric ≥6 years).
- **Severe hepatic impairment:** reduce dose to 5 mg once daily if concurrent renal impairment; otherwise no standard adjustment—use caution.
- **Hemodialysis:** avoid use (minimally dialyzable).
## Contraindications
- Hypersensitivity to cetirizine, hydroxyzine, or any excipients.
- End-stage renal disease (CrCl <10 mL/min) — not studied.
## Adverse Effects
- Somnolence, fatigue, dry mouth (less than first-generation antihistamines).
- Headache, pharyngitis, dizziness (relatively infrequent).
- Children: paradoxical excitation possible.
## Key Drug Interactions
- **CNS depressants (e.g., alcohol, benzodiazepines, opioids):** additive sedation.
- **Theophylline (400 mg/day):** may decrease clearance of cetirizine (minor, clinical relevance uncertain).
## Monitoring
- Symptom control (rhinitis, urticaria)
- Sedation or CNS side effects, especially in patients operating machinery.
- Renal function before initiating in older adults or those with renal disease.
## Clinical Pearls
- Faster onset (~1 hour) vs. loratadine (~2–3 hours).
- Pregnancy category B (epidemiologic data reassuring); avoid first trimester if possible.
- Sedation is dose-dependent — start at 5 mg if patient is sensitive.
- Syrup and chewable tablets available for pediatric use.
- Do not switch between different salt forms (cetirizine HCl vs. cetirizine free base) without checking bioavailability.
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*Educational disclaimer: This information is for educational purposes and does not replace current prescribing information. Always verify dosing, approvals, and local guidelines before clinical use.*
