Cetirizine
Zyrtec | Reactine | Alerid
Overview
Second-generation antihistamine used for allergic rhinitis and chronic urticaria with minimal sedation.
Indications
- Seasonal allergic rhinitis
- Perennial allergic rhinitis
- Chronic idiopathic urticaria
Contraindications
- Hypersensitivity to cetirizine, hydroxyzine, or levocetirizine
- Severe renal impairment (CrCl <10 mL/min) on dialysis
Classification
Mechanism of Action
Selective peripheral H1-receptor antagonist. Metabolite of hydroxyzine with reduced CNS penetration and less sedation.
Pharmacodynamics
Inhibits histamine-mediated early-phase allergic response. Also reduces eosinophil chemotaxis and late-phase allergic inflammation.
Pharmacokinetics
- Absorption
- Rapidly absorbed. Onset 20-60 minutes. Not affected by food.
- Distribution
- Does not significantly cross blood-brain barrier (less sedation vs first-gen).
- Metabolism
- Minimal hepatic metabolism. Primarily excreted unchanged.
- Excretion
- Renal (70% unchanged), fecal (10%).
- Half-life
- 8-9 hours (adults); 6 hours (children)
- Bioavailability
- >70%
- Protein Binding
- 93%
Dosage
Typical dosage: 5-10mg once daily
Available Forms
- Tablet
- Chewable tablet
- Oral solution
- Liquid gel capsule
Side Effects
Common
- Somnolence (14%)
- Fatigue
- Dry mouth
- Headache
- Pharyngitis
Serious
- Anaphylaxis (rare)
- Orofacial dyskinesia (rare)
- Seizures (rare)
Rare
- Hepatitis
- Glomerulonephritis
- Hallucinations
Drug Interactions
May enhance CNS depression despite being a second-generation antihistamine.
Theophylline may slightly decrease cetirizine clearance. Usually not clinically significant.
Warnings
Pregnancy
Category B
Toxicity
LD50 >2000 mg/kg (oral, mouse)
Overdose
Symptoms: somnolence. Treatment: supportive care. Not removed by dialysis.
References
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