====== Fexofenadine ======

===== Classification =====
  * Second-Generation H1 Antihistamine
  * Selective peripheral H1 receptor inverse agonist
  * Active metabolite of terfenadine

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

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

Fexofenadine selectively blocks peripheral H1 receptors.

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

Key Feature:
  * Minimal penetration of the blood-brain barrier
  * Essentially non-sedating at therapeutic doses

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===== Pharmacologic Background =====

Fexofenadine is the active metabolite of terfenadine.

Terfenadine was removed from the market due to QT prolongation and torsades risk (CYP3A4 inhibition interactions).

Fexofenadine:
  * Does not significantly prolong QT interval
  * Does not rely on hepatic metabolism for activation

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===== Pharmacokinetics =====

  * Oral administration
  * Onset: ~1 hour
  * Duration: ~24 hours
  * Primarily eliminated unchanged in feces and urine
  * Minimal hepatic metabolism

Absorption reduced by:
  * Aluminum/magnesium antacids
  * Fruit juices (apple, orange, grapefruit)

Separate dosing from antacids by at least 2 hours.

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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) =====

  * 60 mg PO twice daily
  * OR 180 mg PO once daily

Dose adjustment in renal impairment.

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

Generally very well tolerated.

Possible:
  * Headache
  * Mild nausea
  * Rare dizziness

Sedation:
  * Minimal to none
  * Lowest sedation risk among common 2nd-generation H1 blockers

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

  * Renal impairment (dose adjust)
  * Hypersensitivity

Caution:
  * Avoid coadministration with fruit juice
  * Separate from antacids

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

  * Aluminum/magnesium antacids ↓ absorption
  * Fruit juice ↓ bioavailability
  * Minimal CYP interaction
  * No meaningful QT risk at therapeutic doses

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

  * Least sedating of the second-generation H1 blockers.
  * Preferred in patients requiring full daytime alertness.
  * Safe cardiovascular profile compared to its predecessor (terfenadine).
  * Does not significantly impair cognition or psychomotor function.
  * Not effective for nasal congestion as monotherapy.

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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 | Slightly more sedating |
| [[allergy:drugs:levocetirizine|Levocetirizine]] | Low | Renal | R-enantiomer refinement |
| [[allergy:drugs:fexofenadine|Fexofenadine]] | Minimal | Renal/Fecal | Least sedating; safe QT profile |

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

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