Updated: 12/16/2018

Cholinomimetic Agents

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Direct agonists
  • Most direct agonists are resistant to acetylcholinesterase (AChE)  
    • thereby prevents breakdown of agonist
    • increases cholinergic effect
Direct Agonists Uses Mechanism of Action
Methacholine • Challenge test for bronchial airway hyperactivity/asthma 
• Rapid onset of contraction of smooth muscles in the airways and increases tracheobronchial secretions
• Slightly resistant to acetylcholine-esterase (AChE)
Pilocarpine • Management of glaucoma
• Contracts the pupillary sphincter (miosis) and ciliary muscle (improved accommodation)
• Lowers intraocular pressure by reducing resistance to aqueous humor outflow
• Resistant to AChE
Bethanechol  • Acute postoperative and postpartum urinary retention
• Neurogenic ileus
• Causes bladder contractions which initiates urination
• stimulates gastric motility and tone restoring peristalsis
• Resistant to AChE
Carbachol • Lowers intraocular pressure treating glaucoma
• Pupillary contraction
• Stimulates muscarinic receptors causing miosis 
• Resistant to AChE

 

Indirect Agonists (Cholinesterase Inhibitors)
  • Mechanism of action
    • all work by inhibiting ACHE 
    • thereby preventing the degradation of ACH prolonging its effects
Indirect Agonist
Uses
Notes

Physostigmine 

• Glaucoma
• Atropine overdose or Atropa belladonna (deadly nightshade) ingestion
• CNS penetration
• Absorbs well on all bodily surfaces 
Neostigmine • Postoperative and neurogenic ileus and urinary retention
• Myasthenia gravis
• Reversal of neuromuscular junction blockade (postoperative)

• No CNS penetration
Pyridostigmine  • Myasthenia gravis
• No CNS penetration
Edrophonium • Diagnosis of myasthenia gravis 
• Ileus
• Arrhythmias
• Extremely short lived (5 - 15 min)
Echothiophate • Glaucoma
• Long-lasting (100 hours)
• No CNS penetration
• Insecticides: malathion is safe in humans but parathion is harmful and both can penetrate the CNS
 
Cholinesterase Inhibitor Poisoning
  • Cholinesterase poisoning symptoms 
    • due to ingestion of parathion or cholinesterase inhibitors
    • symptoms result from the overstimulation of systemic cholinergic receptors
      • Glands: sweating, salivation, and lacrimation
      • GI and GU: diarrhea, abdominal cramping, urination
      • Heart: bradycardia
      • Respiratory: bronchospasm
      • Musculoskeletal: skeletal muscle overexcitation
      • Eye: miosis
    • Mnemonic: Diarrhea, Urination, Miosis, Bradycardia, Emesis, Lacrimation, Lethargy, and Salivation
  • Treatment
    • atropine: blocks muscarinic receptors
    • pralidoxime: regenerated AChE
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(M1.PH.14.218) A 16 year-old female is being evaluated for shortness of breath. For the last year she has had shortness of breath and subjective wheezing with exercise and intermittent coughing at night. She reports waking up from sleep coughing 1-2 times per month. She now skips gym class because of her symptoms. She denies any coughing, chest tightness, or shortness of breath on the day of her visit. On exam, her lungs are clear to auscultation bilaterally, with normal inspiratory to expiratory duration ratio. Her pulmonary function tests (PFTs) show normal FEV1 and FVC based on her age, gender, and height. She is told to inhale a medication, and her PFTs are repeated, now showing a FEV1 79% of her previous reading. The patient is diagnosed with asthma. Which of the following medications was used to diagnose the patient? Tested Concept

QID: 101884
1

Methacholine

84%

(113/135)

2

Pilocarpine

1%

(1/135)

3

Bethanechol

8%

(11/135)

4

Carbachol

2%

(3/135)

5

Physostigmine

4%

(5/135)

M 2 E

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