Promethazine is a first-generation antihistamine used to treat N/V, cough, and insomnia by blocking histamine and cholinergic signaling. Its anticholinergic properties can cause side effects like dry mouth, constipation, urine retention, and hyperglycemia. Promethazine is contraindicated in pediatric patients < 2 years because of potentially life-threatening respiratory depression.

Key Points

  • Promethazine [proe METH a zeen] (Phenergan)
    • Mechanism of Action
      • Antagonist at H1 histamine receptors
        • blocks histamine receptors in brain
    • Clinical Use
      • Antiemetic
        • N/V associated with hyperemesis gravidarum and gallstones (cholelithiasis/cholecystitis)
      • Antitussive (cough suppressant)
      • Sedation
        • Used with analgesics in anesthesia
    • Side Effects and Adverse Reactions
      • Anticholinergic effects (sedation, dry mouth, flushing, constipation, respiratory depression, etc.)
      • Contraindicated in patients < 2 years of age (respiratory depression)