Levocetirizine

• Second-Generation H1 Antihistamine
• Selective peripheral H1 receptor inverse agonist
• R-enantiomer of Cetirizine

Parent class: Histamine & Antihistamines

Levocetirizine selectively blocks peripheral H1 receptors.

Effects:

• ↓ Histamine-mediated vasodilation
• ↓ Capillary permeability
• ↓ Pruritus
• ↓ Sneezing and rhinorrhea

As the active R-enantiomer of cetirizine:

• Greater receptor affinity
• Similar efficacy at lower milligram dose

Minimal blood-brain barrier penetration, but mild sedation can still occur.

Cetirizine is a racemic mixture (R + S forms). Levocetirizine is the purified R-enantiomer (active isomer).

Theoretical advantages:

• More selective binding
• Reduced inactive compound exposure
• Potential for fewer adverse effects

Clinically:

• Efficacy and safety are very similar to cetirizine.

• Oral administration
• Rapid onset (~1 hour)
• Duration: ~24 hours
• Primarily renally eliminated
• Minimal hepatic metabolism

Dose adjustment required in renal impairment.

• Allergic Rhinitis
• Chronic idiopathic urticaria
• Seasonal allergies

Effective for:

• Sneezing
• Itching
• Rhinorrhea

Less effective for:

• Nasal congestion (intranasal steroids preferred)

• 5 mg PO once daily
• Reduce dose in renal impairment

Note:

• Lower milligram dose than cetirizine (10 mg) due to purified active isomer.

Generally well tolerated.

Possible:

• Mild drowsiness
• Fatigue
• Headache

Sedation risk:

• Similar to or slightly less than cetirizine
• Still greater than loratadine or fexofenadine

• Severe renal impairment (dose adjust)
• Hypersensitivity to cetirizine or hydroxyzine

Use caution:

• Elderly
• Concomitant CNS depressants

• Minimal CYP involvement
• Additive sedation with alcohol or CNS depressants

• Essentially the active half of cetirizine.
• Similar clinical efficacy to cetirizine.
• Renally cleared — adjust dose accordingly.
• Good for chronic urticaria management.
• Not superior to intranasal corticosteroids for congestion.

• Cetirizine
• Hydroxyzine
• Histamine & Antihistamines
• Allergic Rhinitis – Stepwise Therapy