Cetirizine

# Cetirizine ## Overview - **Classification**: Second-generation antihistamine, H1-receptor antagonist - **Mechanism**: Selectively antagonizes peripheral H1-receptors, blocking histamine release and reducing allergic symptoms like itching, sneezing, and rhinorrhea. ## Primary Indications 1. **Seasonal Allergic Rhinitis (SAR)** - Relief of nasal and non-nasal symptoms caused by seasonal allergens. 2. **Perennial Allergic Rhinitis (PAR)** - Relief of nasal and non-nasal symptoms caused by perennial allergens. 3. **Chronic Idiopathic Urticaria (CIU)** - Treatment of uncomplicated skin manifestations of chronic idiopathic urticaria. ## Adult Dosing ### Standard Dosing **Seasonal/Perennial Allergic Rhinitis & Chronic Idiopathic Urticaria** - **Dose**: **5 mg** or **10 mg** - **Frequency**: Once daily - **Route**: Oral - **Maximum Dose**: **10 mg** per day ### Dose Adjustments - **Renal Impairment**: - **CrCl 31-50 mL/min**: **5 mg** once daily - **CrCl 11-30 mL/min**: **5 mg** every other day - **CrCl <10 mL/min or Dialysis**: Contraindicated - **Hepatic Impairment**: **5 mg** once daily - **Elderly Patients**: Consider **5 mg** once daily initially due to potential decreased renal function. ## Pediatric Dosing ### Neonates (0-28 days) - **Dose**: Not recommended - **Special Notes**: Limited data; risk of increased CNS effects. Consult a specialist if use is considered. ### Infants (6-12 months) - **Dose**: **2.5 mg** - **Frequency**: Once daily - **Route**: Oral solution - **Maximum**: **2.5 mg** per day - **Special Notes**: Safety and efficacy not established in infants < 6 months. ### Children (1-5 years) - **Dose**: **2.5 mg** - **Frequency**: Once daily; may increase to **2.5 mg** BID (total **5 mg/day**) if needed. - **Route**: Oral solution or chewable tablet - **Maximum**: **5 mg** per day - **Special Notes**: Start with lower dose and titrate as needed. ### Children (6-12 years) - **Dose**: **5 mg** or **10 mg** - **Frequency**: Once daily - **Route**: Oral (tablet, chewable, solution) - **Maximum**: **10 mg** per day - **Special Notes**: Lower dose **(5 mg)** recommended initially. ### Adolescents (13-18 years) - **Dose**: **5 mg** or **10 mg** - **Frequency**: Once daily - **Route**: Oral - **Maximum**: **10 mg** per day - **Special Notes**: Follow adult dosing recommendations. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to cetirizine, hydroxyzine, or any piperazine derivative. - **Absolute**: End-stage renal disease (CrCl < 10 mL/min). ### Common Adverse Effects - **Common (1-10%)**: Drowsiness, fatigue, dry mouth, headache, dizziness. - **Serious but Rare**: Angioedema, hepatotoxicity (very rare), severe hypersensitivity reactions. ### Key Drug Interactions - **CNS Depressants (e.g., alcohol, sedatives)**: Increased CNS depression (drowsiness, impaired performance). Avoid concurrent use. - **Theophylline (high doses >400 mg daily)**: Decreased cetirizine clearance, potential for increased cetirizine effects. ## Monitoring & Follow-up - **Before Treatment**: No specific baseline tests required. Assess renal/hepatic function if indicated. - **During Treatment**: Monitor for symptom relief and adverse effects (e.g., drowsiness, dry mouth). - **Clinical Signs**: Watch for excessive sedation or paradoxical excitation in children. ## Clinical Pearls - 💡 **Timing**: May be taken in the evening if sedation is bothersome, as effects are generally sustained for 24 hours. - 💡 **Onset of Action**: Typically provides symptom relief within 1 hour. - 💡 **Food Impact**: Can be taken with or without food. - 💡 **Sedation**: While considered "non-drowsy" for most, individual responses vary; caution patients, especially with driving/operating machinery. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.