Cholinergic Antagonists
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What is the primary function of cholinergic antagonists?

  • To bind to cholinoceptors and enhance the effects of acetylcholine
  • To stimulate muscarinic receptors
  • To bind to cholinoceptors and prevent the effects of acetylcholine (correct)
  • To increase the production of acetylcholine

    • What type of receptors do antimuscarinic agents block?

  • Nicotinic receptors
  • Muscarinic receptors (correct)
  • Adrenergic receptors
  • Dopaminergic receptors

    • What is the effect of atropine on the eye?

  • Miosis (constriction of the pupil)
  • Mydriasis (dilation of the pupil) (correct)
  • Photophobia (sensitivity to light)
  • Hyperemia (increased blood flow)

    • What is the duration of action of atropine?

    <p>Lasts for hours</p> Signup and view all the answers

    What is the effect of atropine on sweat glands?

    <p>Inhibition of sweat glands</p> Signup and view all the answers

    What type of antagonists are used as skeletal muscle relaxant adjuvants?

    <p>Neuromuscular-blocking agents</p> Signup and view all the answers

    What is the effect of anticholinergic drugs on skeletal muscle?

    <p>No effect on skeletal muscle</p> Signup and view all the answers

    Which of the following acts on muscarinic receptors?

    <p>Both A and B</p> Signup and view all the answers

    What is the action of atropine on the brain?

    <p>Both central and peripheral inhibition</p> Signup and view all the answers

    What is atropine used to treat in terms of cardiovascular health?

    <p>Bradycardia</p> Signup and view all the answers

    What is atropine used as in respiratory tracts prior to surgery?

    <p>Antisecretory agent</p> Signup and view all the answers

    What type of poisoning can atropine be used to treat?

    <p>All of the above</p> Signup and view all the answers

    What is the primary route of elimination for atropine?

    <p>Urine</p> Signup and view all the answers

    What is a common adverse effect of atropine?

    <p>Dry mouth</p> Signup and view all the answers

    What can be used to overcome atropine toxicity?

    <p>Physostigmine</p> Signup and view all the answers

    Why is atropine dangerous in children?

    <p>They are more sensitive to its effects</p> Signup and view all the answers

    What is a difference between atropine and scopolamine?

    <p>Scopolamine has a longer duration of action</p> Signup and view all the answers

    What is a characteristic of scopolamine compared to atropine?

    <p>It has a stronger CNS effect</p> Signup and view all the answers

    What is the primary use of benztropine and trihexyphenidyl?

    <p>Managing Parkinson's disease and other parkinsonian syndromes</p> Signup and view all the answers

    What is the mechanism of action of oxybutynin and other antimuscarinic agents?

    <p>Competitive blockade of muscarinic (M3) receptors</p> Signup and view all the answers

    Which of the following is a common side effect of antimuscarinic agents?

    <p>Dry mouth</p> Signup and view all the answers

    What is the therapeutic use of darifenacin and solifenacin?

    <p>Management of overactive bladder and urinary incontinence</p> Signup and view all the answers

    What is the primary route of metabolism for most antimuscarinic agents?

    <p>Hepatic metabolism by the cytochrome P450 system</p> Signup and view all the answers

    What is unique about trospium compared to other antimuscarinic agents?

    <p>It undergoes ester hydrolysis</p> Signup and view all the answers

    What is the benefit of extended-release formulations of oxybutynin and tolterodine?

    <p>Once-daily dosing</p> Signup and view all the answers

    What is the advantage of darifenacin and solifenacin over other antimuscarinic agents?

    <p>They are more selective M3 muscarinic receptor antagonists</p> Signup and view all the answers

    What is a common adverse effect of antimuscarinic agents that affects the eye?

    <p>Blurred vision</p> Signup and view all the answers

    What is the primary therapeutic use of succinylcholine?

    <p>Rapid endotracheal intubation during anesthesia induction</p> Signup and view all the answers

    What is the primary mechanism of succinylcholine's short duration of action?

    <p>Rapid hydrolysis by plasma pseudocholinesterase</p> Signup and view all the answers

    What is the purpose of administering a small dose of nondepolarizing neuromuscular blocker prior to succinylcholine?

    <p>To prevent the adverse effects of succinylcholine</p> Signup and view all the answers

    What is a potential complication of succinylcholine in patients with electrolyte imbalances?

    <p>Prolonged apnea</p> Signup and view all the answers

    What is the effect of succinylcholine on potassium levels?

    <p>Increases potassium release from intracellular stores</p> Signup and view all the answers

    Why is succinylcholine used cautiously in burn patients?

    <p>Because of the risk of hyperkalemia</p> Signup and view all the answers

    What is the route of administration of succinylcholine?

    <p>Intravenous</p> Signup and view all the answers

    What is the effect of discontinuing succinylcholine?

    <p>The effects of succinylcholine rapidly disappear</p> Signup and view all the answers

    What is another therapeutic use of succinylcholine?

    <p>Electroconvulsive shock treatment</p> Signup and view all the answers

    What is scopolamine used for therapeutically?

    <p>Preventing motion sickness and postoperative nausea and vomiting</p> Signup and view all the answers

    What is a unique effect of scopolamine?

    <p>Blocking short-term memory</p> Signup and view all the answers

    What is a potential problem with scopolamine?

    <p>It can produce excitement at higher doses</p> Signup and view all the answers

    How does scopolamine differ from atropine?

    <p>Scopolamine produces sedation, while atropine does not</p> Signup and view all the answers

    What is the pharmacokinetics of scopolamine similar to?

    <p>Atropine</p> Signup and view all the answers

    What is ipratropium classified as?

    <p>Short-acting muscarinic antagonist (SAMA)</p> Signup and view all the answers

    What is the route of administration for ipratropium and tiotropium?

    <p>Inhalation</p> Signup and view all the answers

    What is the effect of the positive charge on these drugs?

    <p>They do not enter the systemic circulation or the CNS</p> Signup and view all the answers

    What is the duration of action of tropicamide?

    <p>6 hours</p> Signup and view all the answers

    Study Notes

    Cholinergic Antagonists

    • Cholinergic antagonists bind to cholinoceptors and prevent the effects of acetylcholine (ACh) and other cholinergic agonists.
    • There are three types of cholinergic antagonists:
      • Antimuscarinic agents (e.g., atropine, scopolamine)
      • Ganglionic blockers (e.g., nicotinic receptors of sympathetic and parasympathetic ganglia)
      • Neuromuscular-blocking agents (e.g., nicotinic antagonists, used as skeletal muscle relaxant adjuvants in anesthesia)

    Antimuscarinic Agents

    • Antimuscarinic agents block muscarinic receptors, causing inhibition of muscarinic functions.
    • Examples: atropine, scopolamine, and some antihistamines and antidepressants (mainly tricyclic antidepressants).
    • Atropine:
      • Tertiary amine belladonna alkaloid with high affinity for muscarinic receptors.
      • Acts both centrally and peripherally.
      • General actions last about 4 hours, except when placed topically in the eye, where the action may last for days.
      • Neuroeffector organs have varying sensitivity to atropine.
      • Greatest inhibitory effects are on bronchial tissue and the secretion of sweat and saliva.
    • Actions of atropine:
      • Eye: blocks muscarinic activity in the eye, resulting in mydriasis, unresponsiveness to light, and cycloplegia.
      • Cardiovascular: used to treat bradycardia of varying etiologies.
      • Antisecretory: used to block secretions in the upper and lower respiratory tracts prior to surgery.
      • Antidote for cholinergic agonists: used to treat organophosphate poisoning, overdose of anticholinesterases, and some types of mushroom poisoning.

    Pharmacokinetics and Adverse Effects of Atropine

    • Atropine is readily absorbed, partially metabolized by the liver, and eliminated primarily in urine.
    • Half-life is about 4 hours.
    • Adverse effects:
      • Dry mouth
      • Blurred vision
      • "Sandy eyes"
      • Tachycardia
      • Urinary retention
      • Constipation
      • Effects on the CNS include restlessness, confusion, hallucinations, and delirium.

    Scopolamine

    • Scopolamine is a tertiary amine plant alkaloid with peripheral effects similar to those of atropine.
    • Greater action on the CNS (unlike atropine, CNS effects are observed at therapeutic doses).
    • Longer duration of action as compared to atropine.
    • Actions:
      • Blocks short-term memory.
      • Produces sedation, but at higher doses, can produce excitement.
      • May produce euphoria and is susceptible to abuse.
    • Therapeutic uses:
      • Prevention of motion sickness.
      • Postoperative nausea and vomiting.

    Other Antimuscarinic Agents

    • Ipratropium, tiotropium, aclidinium, and glycopyrrolate:
      • Quaternary derivatives of atropine or synthetic quaternary compounds.
      • Used as bronchodilators for maintenance treatment of bronchospasm associated with chronic obstructive pulmonary disease (COPD).
      • Delivered via inhalation.
    • Tropicamide and cyclopentolate:
      • Used as ophthalmic solutions for mydriasis and cycloplegia.
      • Duration of action is shorter than that of atropine.
    • Benztropine and trihexyphenidyl:
      • Used as adjuncts with other antiparkinsonian agents to treat Parkinson's disease and other types of parkinsonian syndromes.
    • Oxybutynin and other antimuscarinic agents for overactive bladder:
      • Synthetic atropine-like drugs with antimuscarinic actions.
      • Actions:
        • Competitively block muscarinic (M3) receptors in the bladder, lowering intravesical pressure, increasing bladder capacity, and reducing the frequency of bladder contractions.
        • May cause adverse effects, including dry mouth, constipation, and blurred vision.

    Succinylcholine

    • Neuromuscular-blocking agent (nicotinic antagonist).
    • Used in anesthesia to provide rapid muscle relaxation.
    • Therapeutic uses:
      • Rapid endotracheal intubation during the induction of anesthesia.
      • Electroconvulsive shock treatment.
    • Pharmacokinetics:
      • Administered intravenously.
      • Brief duration of action results from redistribution and rapid hydrolysis by plasma pseudocholinesterase.
      • Continuous infusion can be used to maintain a longer duration of effect.
    • Adverse effects:
      • Hyperthermia (malignant hyperthermia in susceptible patients).
      • Apnea (prolonged apnea due to paralysis of the diaphragm, especially in patients with electrolyte imbalances).
      • Hyperkalemia (rapid release of potassium from intracellular stores, particularly dangerous in burn patients and patients with massive tissue damage).

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    Description

    This quiz covers the pharmacology of cholinergic antagonists, including their effects on muscarinic and nicotinic receptors.

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