II. Mechanism: Muscarinic Antagonists

  1. M1, M4, M5 Receptor Antagonist (CNS Effects)
    1. Altered Mental Status
  2. M2 Receptor Antagonist (Cardiac Effects)
    1. Increased AV Nodal Conduction (Tachycardia, Arrhythmias)
  3. M3 Receptor Antagonist (Smooth Muscle and Exocrine Glands)
    1. Decreased gastrointestinal motility
    2. Decreased Salivation
    3. Decreased Bladder contractions and increased Urethral sphincter tone
    4. Bronchodilation and decreased Bronchial secretions
    5. Mydriasis
    6. Decreased Sweating

III. Mechanism: Nicotinic Antagonists

  1. Ganglionic Blocking Agents (act at Autonomic Nervous System)
    1. Sympathetic effects
      1. Vasodilation
    2. Parasympathetic effects
      1. Mydriasis
      2. Decreased gastrointestinal motility and Constipation
      3. Tachycardia
      4. Urinary Retention
  2. Neuromuscular Blocking Agents (act at Neuromuscular Junction)
    1. Background
      1. Acetylcholine acts at the Neuromuscular Junction (NMJ) with 2 of 5 receptor sites specific for Acetylcholine binding
      2. When both Acetylcholine receptors are bound, ion channels open allowing Sodium influx and Membrane Depolarization
      3. Resulting impulse triggers muscular contraction
    2. Nondepolarizing Neuromuscular Blocking Agent (Vecuronium, Rocuronium)
      1. Acetylcholine Competitive Receptor Antagonists
      2. Inhibited Muscle Contraction (Muscle relaxation, paralysis)
    3. Depolarizing Neuromuscular Blocking Agent (Succinylcholine)
      1. Competitive Cholingergic Agonist
      2. Succinylcholine is an Agonist that binds and blocks Acetylcholine from binding until it dissociates from receptor site
      3. Transient muscle Fasciculations and contractions (due to Agonist activity), followed by paralysis

IV. Medications: Muscarinic Antagonists

  1. Background
    1. Agents listed here are specifically indicated for their Anticholinergic activity
    2. Contrast with other agents with Anticholinergic activity as an adverse effect (e.g. Antihistamines, Tricyclic Antidepressants)
      1. See Anticholinergic Toxicity
  2. Belladona Alkaloids
    1. Atropine
      1. Prototypal CholinergicAntagonist against which other agents are compared
      2. Extracted from plants such as deadly nightshade (atropa belladona)
      3. Used in Unstable Bradycardia and Bladder spasms (e.g. B&O suppositories)
    2. Scopolamine
      1. Used in Motion Sickness and perioperative Nausea and Vomiting
    3. Hyoscyamine (Levsin)
      1. Used as a gastrointestinal antispasmodic agents
  3. Synthetic tertiary agents
    1. Gastrointestinal Antispasmodic Agents
      1. Dicyclomine (Bentyl)
      2. Mebeverine
      3. Oxyphencyclimine
      4. Trimebutine
    2. Bladder Antispasmodic
      1. Oxybutynin (Ditropan)
      2. Flavoxate (Urispas)
      3. Tolterodine (Detrol)
    3. Treatment of Parkinsonism, Extrapyramidal Side Effects and other Movement Disorders
      1. Trihexylphenidyl (Artane)
      2. Biperiden (Akineton)
      3. Procyclidine (Kemadrin)
      4. Benztropine (Cogentin)
    4. Ocular (Cycloplegic, Mydriatic)
      1. Homatropine
  4. Synthetic quaternary agents
    1. Gastrointestinal Antispasmodic Agents
      1. Methscopolamine Bromide (Pamine)
      2. Clidinium (Bromide)
      3. Glycopyrolate (Robinul)
      4. Isopropamide
      5. Methantheline
      6. Tridihexethyl

VI. Complications

  1. See Anticholinergic Toxicity
  2. Altered Level of Consciousness (esp. elderly)
    1. Delirium or confusion (may mimic Dementia)
    2. Memory Impairment
    3. Delirium
    4. Obtundation

VIII. References

  1. Olson (2020) Clinical Pharmacology, Medmaster, Miami, p. 28-9

Images: Related links to external sites (from Bing)

Related Studies