Levocetirizine is a second-generation antihistamine and the active enantiomer of cetirizine. It selectively antagonizes peripheral H₁ histamine receptors, blocking histamine-mediated allergic responses. Key features include:

1. Peripheral Selectivity: Minimizes central nervous system (CNS) penetration, reducing sedation (Lippincott).
2. Potency: As the R-enantiomer of cetirizine, it offers enhanced binding affinity to H₁ receptors, allowing lower therapeutic doses.
3. Anti-inflammatory Effects: Inhibits eosinophil chemotaxis and adhesion molecule expression, reducing late-phase allergic reactions.

Levocetirizine is indicated for:

1. Allergic Rhinitis:
   • Seasonal (hay fever) and perennial allergic rhinitis.
2. Chronic Spontaneous Urticaria:
   • Reduces pruritus, wheals, and flares.
3. Off-Label Uses:
   • Atopic dermatitis, allergic conjunctivitis (as adjunct therapy).

Adults and Adolescents (≥12 years):

• Oral: 5 mg once daily.

Children:

• 6–11 years: 2.5 mg once daily (BNF).
• 2–5 years: 1.25 mg once daily (use oral drops if available).

Renal Impairment:

• Creatinine Clearance (CrCl) 30–50 mL/min: 5 mg every other day.
• CrCl 10–30 mL/min: 5 mg twice weekly.
• CrCl <10 mL/min: Contraindicated (BNF).

Hepatic Impairment:

• No dose adjustment required unless combined with renal impairment.

Administration:

Take with or without food; avoid alcohol (may enhance drowsiness

• Common (1–10%): Headache, dry mouth, fatigue, somnolence.
• Rare (<1%):
  • Dizziness, nausea, diarrhea.
  • Hypersensitivity reactions (angioedema, rash).
  • Isolated reports of urinary retention or blurred vision (anticholinergic effects).

1. Contraindications:
   • Severe renal impairment (CrCl <10 mL/min).
   • Hypersensitivity to levocetirizine, cetirizine, or hydroxyzine.
2. Pregnancy/Lactation:
   • BNF Category: Use only if benefits outweigh risks (limited human data).
   • Excreted in breast milk; avoid during lactation.
3. Elderly: Monitor for dizziness or falls.
4. Activities Requiring Alertness: Caution when driving or operating machinery.

Levocetirizine has minimal metabolic interactions (excreted largely unchanged in urine). Notable considerations:

• CNS Depressants: Alcohol, benzodiazepines, opioids—may enhance sedation.
• P-glycoprotein Inhibitors: Limited evidence, but drugs like ritonavir may theoretically increase plasma levels.
• Theophylline: No significant interaction observed (Lange).

• Generic: Levocetirizine dihydrochloride.
• Brand Names:
  • UK: Xyzal®, Levrix®.
  • US: Xyzal®.
  • Others: Triz® (India), Vozet® (Europe).