Introduction
Levocetirizine is a second-generation antihistamine that is used to treat symptoms associated with chronic allergic rhinitis and uncomplicated cases of chronic idiopathic urticaria. It is the R enantiomer of cetirizine and has a greater affinity for the histamine H1 receptor than cetirizine. Levocetirizine was granted FDA approval in 19951.
Mechanism of Action
Levocetirizine is an antihistamine that selectively competes with histamine for H1-receptor sites on effector cells in the gastrointestinal tract, blood vessels, and respiratory tract. Levocetirizine, the active enantiomer of cetirizine, has twice the binding affinity at the H1-receptor compared to cetirizine2. This action prevents histamine from activating this receptor and causing effects like smooth muscle contraction, increased permeability of vascular endothelium, histidine uptake in basophils, stimulation of cough receptors, and stimulation of flare responses in the nervous system1.
Pharmacokinetics
Following a 5mg oral dose of levocetirizine, a Cmax of 0.27±0.04µg/mL with a Tmax of 0.75±0.50h is observed. The AUC of levocetirizine is 2.31±0.50µg*h/mL. Taking levocetirizine with food does not affect the AUC but delays Tmax by 1.25 hours and lowers Cmax by 36%1. Levocetirizine is minimally metabolized (<14%) via aromatic oxidation, N and O-dealkylation (via CYPA4), and taurine conjugation. It is excreted in the urine (85.4%) and feces (12.9%)2.
Indications
Levocetirizine is indicated to treat symptoms of perennial allergic rhinitis and uncomplicated skin manifestations of chronic idiopathic urticaria. It is also used over the counter for a variety of mild allergy symptoms1.
Adverse Effects
Patients are cautioned to avoid tasks that require complete alertness, as levocetirizine may cause somnolence in susceptible individuals. Use caution in patients with factors predisposing to urinary retention1.
Conclusion
Levocetirizine is a potent and selective antagonist of peripheral H1-receptors. The pharmacokinetic profile of levocetirizine makes it suitable for once-daily administration. It is generally well tolerated, with the most common side effects being somnolence, nasopharyngitis, fatigue, dry mouth, and pharyngitis. Levocetirizine does not significantly interact with other drugs and is not significantly metabolized in humans. It is a suitable choice for the treatment of allergic rhinitis and chronic idiopathic urticaria.
