Notes on Cholinergic Drugs, Anticholinergic Drugs, and Anti-Parkinson's Drugs

Overview of the Autonomic Nervous System

  • The autonomic nervous system (ANS) controls involuntary bodily functions and is divided into two main branches:

    • Sympathetic Nervous System: Responsible for 'fight or flight' responses:

    • Accelerates heartbeat

    • Inhibits digestive activity

    • Stimulates glucose release

    • Stimulates secretion of epinephrine and norepinephrine

    • Dilates pupils

    • Parasympathetic Nervous System: Responsible for 'rest and digest' responses:

    • Slows heartbeat

    • Stimulates digestive activity

    • Contracts pupils

Cholinergic Drugs

  • Definition: Cholinergic drugs mimic the activity of acetylcholine, affecting both muscarinic and nicotinic receptors.
    • Cholinergic Agonists: Also known as parasympathomimetics, they enhance the functions of the parasympathetic nervous system:
    • Eye: Constrict pupils; increase accommodation
    • Lungs: Bronchial constriction; increase secretions
    • Cardiovascular: Decrease pulse and blood pressure through vasodilation; slow conduction of AV node
    • GI Tract: Increase tone, motility, and peristalsis; relax sphincter muscles
    • GU Tract: Increase ureter tone; contract bladder and relax sphincter muscles, stimulate urination
    • Glands: Enhance salivation, perspiration, and tears
    • Striated Muscle: Improve neuromuscular transmission; maintain muscle strength and tone

Direct-Acting Cholinergic Drugs

  • Focused on muscarinic receptors located in smooth muscles (heart, GI, GU, and glands):
    • Examples:
      • Metoclopramide: Increases gastric emptying
      • Pilocarpine: Constricts pupils
      • Bethanechol chloride: Contracts bladder

Bethanechol

  • Contraindications:
    • Bradycardia
    • Hypotension
    • Asthma and COPD
    • Peptic ulcer
    • Parkinsonism
  • Side Effects:
    • Blurred vision, miosis (pinpoint pupils), hypotension, bradycardia, sweating, increased salivation, nausea, vomiting, diarrhea, abdominal cramps, bronchoconstriction

Indirect-Acting Cholinergic Drugs

  • Function: Break down cholinesterase into choline and acetic acid, allowing acetylcholine to activate receptors.
    • Desired Therapeutic Effects:
    • Stimulate skeletal muscles; increase tone
    • Improve memory in Alzheimer's disease
  • Contraindications: Intestinal and urinary obstruction; caution in bradycardia, asthma, peptic ulcers
  • Side Effects:
    • Greater GI motility, bradycardia, miosis, bronchial constriction, promote urination

Cholinergic Crisis

  • Signs (DUMBELLS):
    • Diarrhea and diaphoresis
    • Urination
    • Miosis
    • Bradycardia or tachycardia
    • Emesis (nausea and vomiting)
    • Lacrimation
    • Lethargy
    • Salivation
  • Management: Anticholinergic agents like atropine may be used for treatment.

Cholinergic Antagonists

  • Definition: Cholinergic blocking drugs that inhibit acetylcholine at muscarinic receptors.
    • Effects:
    • Eye: Dilate pupils; decrease accommodation
    • Lungs: Bronchodilation; decrease secretions
    • Heart: Large doses can increase pulse
    • GI Tract: Relax smooth muscle; decrease motility and peristalsis
    • GU Tract: Relax detrusor muscle; increase sphincter constriction
    • Glands: Decrease salivation and perspiration
    • CNS: Decrease tremors and rigidity
  • Examples of Anticholinergic Drugs: Atropine, diphenhydramine, benztropine, tolterodine, ipratropium, scopolamine

Atropine Overdose Symptoms

  • Symptoms of toxicity are often summarized as:
    • "Mad as a hatter" (confusion)
    • "Dry as a bone" (dry mouth)
    • "Hot as a hare" (fever)
    • "Red as a beet" (flushed skin)
    • "Blind as a bat" (dilated pupils)

Anti-Parkinson Drugs

  • Drug Categories:

    • Monoamine Oxidase Type B Inhibitors (e.g., Selegiline):

    • Mechanism of Action: Inhibit breakdown of dopamine;

    • Side Effects: Headache, nausea, orthostatic hypotension;

    • Food Interactions: Avoid tyramine-rich foods to prevent severe hypertension.

    • Dopamine Receptor Agonists (e.g., Ropinirole): Stimulate dopamine receptors; used in various stages of Parkinson's disease.

    • Dopamine Replacement Drugs (e.g., Carbidopa/Levodopa):

    • Mechanism: Levodopa is converted to dopamine with the help of Carbidopa, which prevents premature breakdown.

    • Side Effects: Cardiac dysrhythmias, dyskinesia, nausea.

    • Caution with high protein diets as they can hinder absorption.

    • Anticholinergic Drugs (e.g., Benztropine): reduce tremors and rigidity associated with Parkinson's disease.

Nursing Process for Cholinergic and Anticholinergic Drugs

  • Key elements: Assessment, Diagnosis, Planning, Implementation, and Evaluation practices are essential in managing these medications effectively.

Practice Questions

  1. Patient assessment after atropine administration: What to assess? A. Nausea B. Tachycardia C. Rales D. Hypotension
  2. Evaluation of atropine effectiveness in a preoperative patient: Patient should state C. "My mouth feels dry."
  3. Administration protocol for cholinergic crisis: Medications A. atropine sulfate or C. edrophonium.
  4. Effectiveness of pyridostigmine in myasthenia gravis should show A. Increased muscle strength.