====== Cetirizine ======

===== Classification =====
  * Second-Generation H1 Antihistamine
  * Peripheral H1 receptor inverse agonist
  * Active metabolite of hydroxyzine

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

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

Cetirizine selectively blocks peripheral H1 receptors.

Effects:
  * ↓ Histamine-mediated vasodilation
  * ↓ Capillary permeability
  * ↓ Pruritus
  * ↓ Sneezing and rhinorrhea

Compared to first-generation antihistamines:
  * Minimal anticholinergic activity
  * Limited blood-brain barrier penetration
  * Low but not zero sedation

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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
  * Pruritus

Effective for:
  * Sneezing
  * Itching
  * Rhinorrhea

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

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

  * 10 mg PO once daily
  * Consider 5 mg daily in renal impairment

Pediatric dosing based on age.

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

Generally well tolerated.

Possible:
  * Mild drowsiness (more than loratadine)
  * Fatigue
  * Dry mouth (rare)

Sedation risk:
  * Higher than loratadine
  * Lower than diphenhydramine

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

  * Severe renal impairment (dose adjust)
  * Hypersensitivity

Use caution:
  * Elderly
  * Concomitant CNS depressants

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

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

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

  * Slightly more effective for urticaria than loratadine.
  * Slightly more sedating than loratadine.
  * Good balance of potency and tolerability.
  * Renal clearance makes it safer in hepatic disease.

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

^ Drug ^ Sedation Risk ^ Elimination ^ Notes ^
| [[allergy:drugs:loratadine|Loratadine]] | Very low | Hepatic (CYP3A4) | Active metabolite = desloratadine |
| [[allergy:drugs:cetirizine|Cetirizine]] | Low | Renal | Active metabolite of hydroxyzine |
| [[allergy:drugs:fexofenadine|Fexofenadine]] | Minimal | Renal | Least sedating |

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

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