Cetirizine (ctz)

# Cetirizine (ctz) ## Overview Cetirizine is a second-generation, non-sedating (though potentially mildly sedating) histamine H1-receptor antagonist. It is a major metabolite of hydroxyzine and possesses high affinity for peripheral H1 receptors with minimal anticholinergic effects. ## Primary Indications * Seasonal and perennial allergic rhinitis. * Chronic idiopathic urticaria (hives). ## Adult Dosing * **Standard dose:** 5–10 mg orally once daily. * **Maximum dose:** 10 mg per 24 hours. ## Pediatric Dosing * **Children 6 to 11 years:** 5–10 mg once daily. * **Children 2 to 5 years:** 2.5 mg once daily; may increase to 5 mg once daily if clinically required. * **Children 6 months to <2 years:** 2.5 mg once daily. * *Note:* Dosing for children <6 months is not FDA-approved and requires specialist consultation. ## Dose Adjustments * **Renal Impairment:** Adjust dose in moderate-to-severe renal impairment (CrCl <50 mL/min). Generally, 5 mg once daily is recommended. * **Hepatic Impairment:** Dose reduction (5 mg once daily) may be required in patients with hepatic impairment. * **Elderly:** Start at the lowest effective dose (5 mg) due to potential for increased sensitivity and risk of sedation. ## Contraindications * Hypersensitivity to cetirizine, hydroxyzine, or levocetirizine. * Severe renal impairment (CrCl <10 mL/min) or patients on hemodialysis. ## Adverse Effects * **Common:** Somnolence, fatigue, headache, dizziness, dry mouth, and pharyngitis. * **Rare/Significant:** Paradoxical CNS stimulation (more common in children), urinary retention (rare), and severe withdrawal pruritus upon discontinuation (rare). ## Key Drug Interactions * **CNS Depressants:** Concomitant use with alcohol, benzodiazepines, or opioids may increase sedative effects. * **Theophylline:** May decrease the clearance of cetirizine, potentially increasing systemic exposure. * **Anticholinergics:** May theoretically add to the anticholinergic burden, though cetirizine has low affinity for muscarinic receptors. ## Monitoring * Monitor for excessive sedation or cognitive impairment, especially in elderly patients. * Assess symptom relief and treatment efficacy. ## Clinical Pearls * **Sedation Potential:** While classified as "non-sedating," cetirizine is more sedating than fexofenadine or loratadine; patients should be advised to monitor their response before operating machinery. * **Onset:** Typically begins working within 60 minutes. * **Duration:** Full effects generally persist for 24 hours. * **Dosing Timing:** May be taken with or without food. If sedation occurs, switching to evening administration is often effective. *** *Disclaimer: This information is for educational purposes and does not replace professional clinical judgment. Always verify current prescribing information, institutional protocols, and specific patient contraindications before prescribing or administering medication.*