Cholinergic Antagonists
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Questions and Answers

What is the general term for agents that bind to cholinoceptors and prevent the effects of acetylcholine (ACh) and other cholinergic agonists?

  • Nicotinic receptor antagonist
  • Cholinergic agonist
  • Muscarinic receptor blocker
  • Cholinergic antagonist (correct)

    • What is the most clinically useful type of cholinergic antagonist?

  • Selective blockers of muscarinic receptors (correct)
  • Neuromuscular-blocking agents
  • Ganglionic blockers
  • Nicotinic receptor antagonists

    • What is a therapeutic use of atropine in the eye?

  • To treat glaucoma
  • To treat myopia
  • To measure refractive errors (correct)
  • To treat conjunctivitis

    • What is another term for anticholinergic agents?

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

    What is atropine used as in the treatment of gastrointestinal issues?

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

    What is the primary mechanism of action of atropine?

    <p>Competitive binding to muscarinic receptors</p> Signup and view all the answers

    What is the effect of anticholinergic drugs on sympathetic neurons?

    <p>Inhibition of only cholinergic sympathetic neurons</p> Signup and view all the answers

    Why is atropine used in cardiovascular issues?

    <p>To treat bradycardia</p> Signup and view all the answers

    What is the primary use of neuromuscular-blocking agents?

    <p>Skeletal muscle relaxation in surgical anesthesia</p> Signup and view all the answers

    What is atropine used for in respiratory tract issues?

    <p>As an antisecretory agent</p> Signup and view all the answers

    What is the effect of anticholinergic drugs on skeletal neuromuscular junctions (NMJs)?

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

    What is atropine used to treat?

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

    How is atropine eliminated from the body?

    <p>Primarily through urine</p> Signup and view all the answers

    What is the structure of atropine?

    <p>Tertiary amine</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

    What happens to the receptor during Phase I?

    <p>It opens the sodium channel.</p> Signup and view all the answers

    What is the effect of the depolarizing agent on the receptor?

    <p>It opens the sodium channel.</p> Signup and view all the answers

    What occurs in Phase I?

    <p>The receptor is depolarized.</p> Signup and view all the answers

    What is the result of the depolarization of the receptor?

    <p>A transient twitch of the muscle.</p> Signup and view all the answers

    What is the relationship between the nicotinic receptor and the sodium channel?

    <p>The nicotinic receptor opens the sodium channel.</p> Signup and view all the answers

    What happens to the receptor after Phase I?

    <p>It becomes desensitized to acetylcholine.</p> Signup and view all the answers

    What is the effect of Succinylcholine on the nicotinic receptor?

    <p>It desensitizes the receptor.</p> Signup and view all the answers

    What happens to the membrane during Phase II?

    <p>It repolarizes.</p> Signup and view all the answers

    What is the effect of a miotic drug on the pupil?

    <p>It constricts the pupil</p> Signup and view all the answers

    What happens to the receptor during the action of depolarizing neuromuscular-blocking drugs?

    <p>It becomes incapable of transmitting further impulses</p> Signup and view all the answers

    What is the effect of continuous depolarization of the receptor?

    <p>It causes gradual dilation of the pupil</p> Signup and view all the answers

    What type of drugs contract the circular muscles of the iris?

    <p>Muscarinic agonists</p> Signup and view all the answers

    What is the mechanism of action of depolarizing neuromuscular-blocking drugs?

    <p>They depolarize the receptor continuously</p> Signup and view all the answers

    What is the effect of muscarinic agonists on the pupil?

    <p>They constrict the pupil</p> Signup and view all the answers

    What happens to the receptor after depolarization by depolarizing neuromuscular-blocking drugs?

    <p>It remains depolarized</p> Signup and view all the answers

    What is the effect of a depolarizing neuromuscular-blocking drug on muscle contraction?

    <p>It causes muscle relaxation</p> Signup and view all the answers

    What is the primary way oxybutynin and tolterodine are metabolized?

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

    What is the advantage of trospium in treating overactive bladder in patients with dementia?

    <p>It has fewer CNS effects</p> Signup and view all the answers

    What is the mechanism of action of ganglionic blockers?

    <p>They block the ion channels of the autonomic ganglia</p> Signup and view all the answers

    What is the effect of nicotine on autonomic ganglia?

    <p>It depolarizes autonomic ganglia, resulting in stimulation and then paralysis</p> Signup and view all the answers

    What is the therapeutic benefit of nicotine?

    <p>It has no therapeutic benefit</p> Signup and view all the answers

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

    <p>They allow for once-daily dosing</p> Signup and view all the answers

    What is the common side effect of oxybutynin and tolterodine?

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

    What is the metabolic pathway of trospium?

    <p>Ester hydrolysis</p> Signup and view all the answers

    Study Notes

    Cholinergic Antagonists

    • Cholinergic antagonists are agents that bind to cholinoceptors (muscarinic or nicotinic) and prevent the effects of acetylcholine (ACh) and other cholinergic agonists.
    • The most clinically useful of these agents are selective blockers of muscarinic receptors, also known as anticholinergic agents, antimuscarinic agents, or parasympatholytics.
    • A second group of drugs, the ganglionic blockers, shows a preference for the nicotinic receptors of the sympathetic and parasympathetic ganglia.
    • The third family of compounds, the neuromuscular-blocking agents, interfere with transmission of efferent impulses to skeletal muscles.

    Antimuscarinic Agents

    • Antimuscarinic agents block muscarinic receptors, causing inhibition of muscarinic functions.
    • They also block the few exceptional sympathetic neurons that are cholinergic, such as those innervating the salivary and sweat glands.
    • These drugs do not block nicotinic receptors and have little or no action at skeletal neuromuscular junctions (NMJs) or autonomic ganglia.

    Atropine

    • Atropine is a tertiary amine belladonna alkaloid with a high affinity for muscarinic receptors.
    • It binds competitively and prevents ACh from binding to those sites.
    • Atropine acts both centrally and peripherally.
    • Therapeutic uses include:
      • Ophthalmic: Topical atropine exerts both mydriatic and cycloplegic effects.
      • Antispasmodic: Atropine is used to relax the GI tract.
      • Cardiovascular: The drug is used to treat bradycardia of varying etiologies.
      • Antisecretory: Atropine is used to block secretions in the upper and lower respiratory tracts prior to surgery.
      • Antidote for cholinergic agonists: Atropine is used to treat organophosphate poisoning and overdose of clinically used anticholinesterases.

    Pharmacokinetics and Adverse Effects of Atropine

    • Atropine is readily absorbed, partially metabolized by the liver, and eliminated primarily in urine.
    • It has a half-life of about 4 hours.
    • Adverse effects include:
      • Dry mouth
      • Blurred vision
      • Tachycardia
      • Urinary retention
      • Constipation
      • Effects on the CNS include restlessness, confusion, hallucinations, and delirium, which may progress to depression, collapse of the circulatory and respiratory systems, and death.

    Ganglionic Blockers

    • Ganglionic blockers specifically act on the nicotinic receptors of both parasympathetic and sympathetic autonomic ganglia.
    • These drugs show no selectivity toward the parasympathetic or sympathetic ganglia and are not effective as neuromuscular antagonists.
    • They block the entire output of the autonomic nervous system at the nicotinic receptor.

    Nicotine

    • Nicotine is a poison with many undesirable actions and is deleterious to health.
    • It is without therapeutic benefit.
    • Depending on the dose, nicotine depolarizes autonomic ganglia, resulting first in stimulation and then in paralysis of all ganglia.
    • The stimulatory effects are complex and result from increased release of neurotransmitters, due to effects on both sympathetic and parasympathetic ganglia.

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    Learn about cholinergic antagonists, agents that bind to cholinoceptors and prevent the effects of acetylcholine, and their clinical uses.

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