Medicine & USMLE

Second Generation Antihistamines

In Progress
  1. Terbutaline
  2. Radioactive Iodine
  3. Ipratropium / Tiotropium
  4. Levothyroxine
  5. Second Generation Antihistamines
  6. First Generation Antihistamines (Diphenhydramine)
  7. Inhaled Steroids
  8. Antitussives
  9. Hypokalemia


Second generation antihistamines include the drugs loratadine, fexofenadine, and cetirizine. They are mainly used to treat seasonal allergies, but can also be used to treat mild allergic reactions, as well as nausea and vomiting. Second generation antihistamines do not cause drowsiness or anticholinergic side effects.

Key Points

  • Second Generation Antihistamines
    • Also called nonsedating antihistamines
    • Key Drugs
      • Loratadine (Claritin)
      • Fexofenadine (Allegra)
      • Cetirizine (Zyrtec)
      • Desloratadine
    • Mechanism
      • Antihistamine
        • Competes with histamine at the H-1 receptor sites to reduce the effects of histamine
    • Clinical Use
      • Allergies
        • Seasonal allergies (sneezing, nasal congestion, etc.)
        • May be used to treat mild allergic reactions, e.g. pruritus (itchiness), hives/rash
      • Nausea and vomiting
    • Side Effects and Adverse Reactions
      • Very few side effects compared to first generation antihistamines.
      • Do not cause drowsiness or anticholinergic effects