Atropine (Homatropine and Tropicamide)

Summary

Atropine and its derivatives, homatropine and tropicamide, are muscarinic antagonists used commonly to treat bradycardia. At the heart, atropine inhibits M2 muscarinic receptors induce an increase in heart rate. In an ophthalmic setting, atropine and related drugs are used to induce pupil dilation or mydriasis, as well as cycloplegia for eye exams. Atropine toxicity can be reversed by administering the drug physostigmine.

Key Points

• Atropine (Homatropine, Tropicamide)
  • Mechanism
    • Muscarinic antagonist
  • Clinical Use
    • Mydriasis (dilation) and cycloplegia (loss of accommodation, lens adjustments)
      • Used for ophthalmic procedures
    • Treats Bradycardia
    • Treats acetylcholinesterase toxicity
    • Occasionally used before procedures to dilate smooth muscle (bronchoscopy) and decrease secretions (mucus)
  • Adverse Effects
    • Flushing
      • Pathogenesis is unknown
    • Anticholinergic effects
      • Decreased sweating increases body temperature (fever), blurry vision due to cycloplegia and mydriasis, tachycardia and flushing, constipation, dry mouth, urinary retention
    • Often memorized using mnemonic: "hot as a hare, dry as a bone, red as a beet, blind as a bat, mad as a hatter, the bowel and bladder loser their tone, and the heart runs alone”
  • Reversal
    • Physostigmine reverses atropine overdose