====== Second-Generation H1 Antihistamines ======

These agents are selective peripheral H1 receptor inverse agonists with minimal central nervous system penetration.

Primary use:
  * [[allergy:clinical:allergic_rhinitis|Allergic Rhinitis]]
  * Chronic urticaria
  * Pruritus

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===== Side-by-Side Comparison =====

^ Drug ^ Usual Adult Dose ^ Sedation Risk ^ Elimination ^ Unique Feature ^
| [[allergy:drugs:loratadine|Loratadine]] | 10 mg daily | Very low | Hepatic (CYP3A4) | Prodrug |
| [[allergy:drugs:desloratadine|Desloratadine]] | 5 mg daily | Very low | Hepatic | Active metabolite |
| [[allergy:drugs:cetirizine|Cetirizine]] | 10 mg daily | Low | Renal | Active metabolite of hydroxyzine |
| [[allergy:drugs:levocetirizine|Levocetirizine]] | 5 mg daily | Low | Renal | R-enantiomer refinement |
| [[allergy:drugs:fexofenadine|Fexofenadine]] | 180 mg daily | Minimal | Renal/Fecal | Least sedating |

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===== Sedation Spectrum (Low → Higher) =====

  * [[allergy:drugs:fexofenadine|Fexofenadine]]
  * [[allergy:drugs:loratadine|Loratadine]]
  * [[allergy:drugs:desloratadine|Desloratadine]]
  * [[allergy:drugs:cetirizine|Cetirizine]]
  * [[allergy:drugs:levocetirizine|Levocetirizine]]

(Note: All far less sedating than first-generation agents.)

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===== Clinical Selection Guide =====

If daytime alertness is critical:
[[allergy:drugs:fexofenadine|Fexofenadine]]

If patient has hepatic impairment:
[[allergy:drugs:cetirizine|Cetirizine]] or [[allergy:drugs:levocetirizine|Levocetirizine]]

If patient has renal impairment:
[[allergy:drugs:loratadine|Loratadine]] or [[allergy:drugs:desloratadine|Desloratadine]]

If chronic urticaria:
[[allergy:drugs:cetirizine|Cetirizine]] commonly effective

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===== Key Board Pearls =====

  * Second-generation agents have minimal anticholinergic effects.
  * Intranasal corticosteroids are superior for nasal congestion.
  * Sedation varies within the class.
  * Fexofenadine has the cleanest CNS profile.
  * Cetirizine and levocetirizine require renal dose adjustment.