====== Levocetirizine ======

===== Classification =====
  * Second-Generation H1 Antihistamine
  * Selective peripheral H1 receptor inverse agonist
  * R-enantiomer of [[allergy:drugs:cetirizine|Cetirizine]]

Parent class: [[allergy:histamine|Histamine & Antihistamines]]

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===== Mechanism of Action =====

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.

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===== Pharmacologic Concept – Enantiomers =====

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.

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===== Pharmacokinetics =====

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

Dose adjustment required in renal impairment.

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===== Indications =====

  * [[allergy:clinical:allergic_rhinitis|Allergic Rhinitis]]
  * Chronic idiopathic urticaria
  * Seasonal allergies

Effective for:
  * Sneezing
  * Itching
  * Rhinorrhea

Less effective for:
  * Nasal congestion (intranasal steroids preferred)

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===== Dosing (Adult) =====

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

Note:
  * Lower milligram dose than cetirizine (10 mg) due to purified active isomer.

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===== Adverse Effects =====

Generally well tolerated.

Possible:
  * Mild drowsiness
  * Fatigue
  * Headache

Sedation risk:
  * Similar to or slightly less than cetirizine
  * Still greater than loratadine or fexofenadine

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===== Contraindications / Cautions =====

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

Use caution:
  * Elderly
  * Concomitant CNS depressants

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===== Drug Interactions =====

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

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===== Clinical Pearls =====

  * 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.

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===== Comparison Within Class =====

^ Drug ^ Sedation Risk ^ Elimination ^ Unique Feature ^
| [[allergy:drugs:loratadine|Loratadine]] | Very low | Hepatic | Active metabolite = desloratadine |
| [[allergy:drugs:cetirizine|Cetirizine]] | Low | Renal | Racemic mixture |
| [[allergy:drugs:levocetirizine|Levocetirizine]] | Low | Renal | Purified R-enantiomer |
| [[allergy:drugs:fexofenadine|Fexofenadine]] | Minimal | Renal | Least sedating |

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===== Related Pages =====

  * [[allergy:drugs:cetirizine|Cetirizine]]
  * [[allergy:drugs:hydroxyzine|Hydroxyzine]]
  * [[allergy:histamine|Histamine & Antihistamines]]
  * [[allergy:clinical:allergic_rhinitis|Allergic Rhinitis – Stepwise Therapy]]