Cholinergic Agonists Overview
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Questions and Answers

Which of the following is a direct-acting cholinomimetic?

  • Physostigmine
  • Edrophonium
  • Bethanechol (correct)
  • Pyridostigmine

Pilocarpine is classified as a choline ester.

False (B)

What is the main clinical application of Bethanechol?

Treatment of paralytic ileus

_________ is a synthetic choline ester that acts on the GIT and urinary bladder.

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

Match the following cholinergic drugs to their classifications:

<p>Bethanechol = Choline ester Pilocarpine = Alkaloid Methacholine = Diagnostic tool Physostigmine = Reversible inhibitor</p> Signup and view all the answers

Which of the following cholinergic drugs cannot cross the blood-brain barrier (BBB)?

<p>Bethanechol (C)</p> Signup and view all the answers

Indirect-acting cholinergic agonists enhance the effect of acetylcholine in the body.

<p>True (A)</p> Signup and view all the answers

What is the significance of methacholine in clinical practice?

<p>It is used as a diagnostic tool.</p> Signup and view all the answers

What medication is used to treat non-obstructive urinary retention?

<p>Bethanechol (D)</p> Signup and view all the answers

Pilocarpine can cross the blood-brain barrier.

<p>True (A)</p> Signup and view all the answers

What is the primary feature of Sjögren's syndrome?

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

Bethanechol stimulates __________ receptors to promote the tone of the detrusor urinae muscle.

<p>muscarinic acetylcholine</p> Signup and view all the answers

Match the following clinical applications with the corresponding medication:

<p>Bethanechol = Paralytic ileus Pilocarpine = Glaucoma</p> Signup and view all the answers

Which medication is primarily used to treat glaucoma?

<p>Pilocarpine (C)</p> Signup and view all the answers

Sjögren's syndrome primarily affects the liver.

<p>False (B)</p> Signup and view all the answers

The main action of pilocarpine in treating xerostomia is to stimulate __________ secretions.

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

What is the primary mechanism of action (MOA) of Bethanechol in treating non-obstructive urinary retention?

<p>Stimulates muscarinic acetylcholine receptors (D)</p> Signup and view all the answers

Bethanechol can cross the blood-brain barrier (BBB).

<p>False (B)</p> Signup and view all the answers

What condition is characterized by the obstruction of the intestine due to paralysis of intestinal muscle?

<p>Paralytic ileus</p> Signup and view all the answers

Bethanechol has a __________ duration of action compared to acetylcholine (Ach).

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

Match the conditions with their relevant causes:

<p>Abdominal surgery = Causes paralytic ileus Certain drugs = Causes paralytic ileus Spinal injuries = Causes paralytic ileus Inflammation within abdomen = Causes paralytic ileus Disease of intestinal muscle = Causes paralytic ileus</p> Signup and view all the answers

Which of the following clinical applications of Bethanechol is correct?

<p>Treatment of paralytic ileus (C)</p> Signup and view all the answers

Bethanechol has a selective action on the urinary bladder and gastrointestinal tract.

<p>True (A)</p> Signup and view all the answers

The activation of muscarinic acetylcholine receptors (mAChR) by Bethanechol __________ gastric motility.

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

What receptor does pilocarpine primarily act on?

<p>M3 (A)</p> Signup and view all the answers

Dry mouth can be treated with cevimeline in patients with Sjögren's syndrome.

<p>True (A)</p> Signup and view all the answers

What is the primary clinical application of carbachol?

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

Pilocarpine facilitates outflow of aqueous humor through the canal of __________.

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

Match the following drugs with their clinical uses:

<p>Pilocarpine = Dry mouth Cevimeline = Glaucoma Carbachol = Miotic agent Bethanechol = Urinary retention</p> Signup and view all the answers

Which of the following adverse effects is NOT associated with muscarinic agonists?

<p>Hypertension (D)</p> Signup and view all the answers

Carbachol is not metabolized by cholinesterase.

<p>True (A)</p> Signup and view all the answers

Name a soluble drug that has CNS effects among anticholinesterases.

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

Overdosage of muscarinic agonists can lead to __________.

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

What is the mechanism of action of pilocarpine in treating glaucoma?

<p>Contraction of ciliary muscle (D)</p> Signup and view all the answers

What is a clinical use of Physostigmine?

<p>Glaucoma (D)</p> Signup and view all the answers

Echothiophate is an irreversible anticholinesterase used for the treatment of glaucoma.

<p>True (A)</p> Signup and view all the answers

Name one symptom of organophosphate toxicity.

<p>Severe bradycardia</p> Signup and view all the answers

Organophosphate agents are categorized as _____ soluble, with the exception of echothiophate.

<p>highly lipid</p> Signup and view all the answers

Match the drug with its clinical use:

<p>Edrophonium = Diagnosis of Myasthenia gravis Neostigmine = Urinary retention Atropine = Block muscarinic actions Pralidoxime = Reactivation of cholinesterase</p> Signup and view all the answers

What class of conditions does Myasthenia gravis predominantly relate to?

<p>Neuromuscular disorders (B)</p> Signup and view all the answers

Pralidoxime can reactivate cholinesterase if given after aging occurs.

<p>False (B)</p> Signup and view all the answers

What is one effect of organophosphate poisoning on skeletal muscles?

<p>Muscle weakness and paralysis</p> Signup and view all the answers

Symptoms of sarin exposure can appear within _____ seconds after exposure to vapor form.

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

Which of the following is NOT a symptom of organophosphate toxicity?

<p>Hypertension (C)</p> Signup and view all the answers

Flashcards

Cholinergic Agonists

Drugs that mimic the effects of acetylcholine, a neurotransmitter that activates the parasympathetic nervous system.

Direct-acting cholinergic agonists

Drugs that directly bind to and activate cholinergic receptors.

Bethanechol

A synthetic cholinergic agonist that selectively targets the gastrointestinal tract and urinary bladder.

Paralytic ileus

Condition where the bowel muscles stop moving after surgery.

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Treatment of paralytic ileus (following surgery)

Using Bethanechol to restore impaired rhythmic peristalsis, and increase gastric motility/tone.

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Cholinergic receptors

Specific receptors in the body that are activated by acetylcholine.

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Muscarinic receptors

Cholinergic receptors that are stimulated by Bethanechol.

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Methacholine

A cholinergic agonist used to diagnose asthma.

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Urinary retention

Inability to completely empty the bladder.

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Causes of Urinary Retention

Acute, postoperative, postpartum, non-obstructive, neurogenic atony of the bladder

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Bethanechol MOA (Urinary Retention)

Activates muscarinic acetylcholine receptors, increasing the tone of the detrusor urinae muscle, causing contraction for micturition (urination).

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Pilocarpine Target

Targets eye and exocrine glands, mainly M3 receptors.

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Pilocarpine Clinical Uses

Treats dry mouth (xerostomia) and glaucoma.

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Xerostomia

Dry mouth.

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Sjӧgrens syndrome

Autoimmune disorder attacking lacrimal and salivary glands, causing dry eyes and dry mouth.

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Pilocarpine MOA (Dry Mouth)

Stimulates salivary secretions.

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Paralytic ileus cause

Paralytic ileus is caused by the interruption of intestinal muscle contractions due to a variety of factors, including abdominal surgery, drugs, spinal injuries, abdominal inflammation, or intestinal muscle disease.

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Bethanechol MOA (paralytic ileus)

Bethanechol activates muscarinic receptors in the GI tract, specifically M3 receptors, increasing gastric motility and tone to restore normal peristalsis.

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Bethanechol's selectivity

Bethanechol primarily affects the gastrointestinal tract (GIT) and urinary bladder; it has a limited effect on other organs.

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Bethanechol duration

Bethanechol lasts longer than the naturally occurring acetylcholine (Ach) it mimics.

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Bethanechol's BBB crossing

Bethanechol does not cross the blood-brain barrier (BBB).

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Paralytic ileus treatment

Bethanechol is used to treat paralytic ileus by stimulating the smooth muscles in the gut to restore normal contractions.

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Non-obstructive urinary retention treatment

Bethanechol treats non-obstructive urinary retention by targeting muscles in the bladder to contract and release urine.

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What are the therapeutic uses of irreversible anticholinesterases?

Irreversible anticholinesterases are used therapeutically in the treatment of glaucoma (e.g., Echothiophate) and as nerve agents (e.g., Tabun, Sarin, Soman, VX).

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How do organophosphate insecticides work?

Organophosphate insecticides inhibit acetylcholinesterase by forming a strong covalent bond, leading to prolonged inhibition of the enzyme.

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What is the mechanism of action of pralidoxime in organophosphate poisoning?

Pralidoxime regenerates recently inhibited cholinesterase by reactivating the enzyme, effectively reversing the effects of organophosphates.

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What are the symptoms of organophosphate toxicity?

Organophosphate toxicity manifests with a range of symptoms including bradycardia, hypotension, bronchospasm, increased GI motility, muscle weakness, convulsions, and coma.

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How does atropine work in the treatment of organophosphate poisoning?

Atropine is a muscarinic antagonist that blocks the effects of acetylcholine at muscarinic receptors, counteracting the cholinergic overstimulation caused by organophosphates.

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Why is atropine less effective in organophosphate poisoning after aging?

After aging, the organophosphate forms an extremely stable bond with acetylcholinesterase, making reactivators like pralidoxime less effective. Atropine still blocks muscarinic effects, but cannot reactivate the enzyme.

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What is the effect of organophosphate aging on acetylcholinesterase?

Aging refers to the process where the organophosphate forms an extremely stable bond with acetylcholinesterase, making enzyme reactivation almost impossible.

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How are organophosphates absorbed?

Organophosphates are readily absorbed through the skin, lungs, gastrointestinal tract, and conjunctiva.

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Muscarinic Effects

Effects of organophosphates on muscarinic receptors, resulting in symptoms like bradycardia, hypotension, bronchospasm, and increased GI motility.

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Nicotinic Effects

Effects of organophosphates on nicotinic receptors, leading to initial skeletal muscle twitching, progressing to weakness and paralysis.

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What is the MOA of Pilocarpine in treating Glaucoma?

Pilocarpine, a muscarinic agonist, acts on M3 receptors, causing contraction of the iris sphincter muscle, reducing pupil size (miosis). This contraction also opens the trabecular network, facilitating aqueous humor outflow through the canal of Schlemm, thereby reducing intraocular pressure.

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How does Pilocarpine differ from Cevimeline?

While both Pilocarpine and Cevimeline are muscarinic agonists, Cevimeline exhibits greater selectivity for M3 receptors, primarily targeting exocrine glands. Pilocarpine, on the other hand, acts on both eye and exocrine gland M3 receptors.

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What are the common adverse effects of Muscarinic Agonists?

Muscarinic agonists can cause excessive salivation, lacrimation, urination, sweating (diaphoresis), gastrointestinal effects, and even vomiting.

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Carbachol

Carbachol is a choline ester that functions as a muscarinic agonist, with both nicotinic and muscarinic activity. It's commonly used in the treatment of glaucoma as a miotic agent.

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What is the role of Anticholinesterases in cholinergic transmission?

Anticholinesterases act by inhibiting the enzyme cholinesterase, which breaks down acetylcholine. This leads to an accumulation of acetylcholine at the synapse, amplifying cholinergic transmission.

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What is the effect of anticholinesterases on the central nervous system?

Only water-soluble anticholinesterases can cross the blood-brain barrier and exert their effects on the central nervous system. This can lead to various CNS side effects.

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Cevimeline

Cevimeline, a muscarinic agonist, acts predominantly on M3 receptors. This selectivity makes it particularly useful in treating the symptoms of dry mouth associated with Sjogren's Syndrome.

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Pilocarpine and its CNS effects.

Pilocarpine, unlike some other muscarinic agonists, can cross the blood-brain barrier, leading to potential central nervous system effects.

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What is the significance of water-soluble anticholinesterases in managing glaucoma?

Water-soluble anticholinesterases can cross the blood-brain barrier, which may not be desirable in the treatment of glaucoma. This contrasts with the preferred use of lipid-soluble anticholinesterases acting more locally in the eye

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Study Notes

Cholinergic Agonists (Parasympathomimetic Agents)

  • Cholinergic agonists mimic the effects of acetylcholine, a neurotransmitter in the parasympathetic nervous system.
  • Learning outcomes include understanding the major cholinergic drug groups and their mechanisms of action, how direct-acting and indirect-acting agonists affect the parasympathetic nervous system, and the therapeutic applications and risks associated with cholinergic drugs.
  • Key groups of cholinoceptor stimulants include choline esters (e.g., pilocarpine, methacholine) and alkaloids (e.g., physostigmine).
  • Direct-acting drugs bind directly to muscarinic and nicotinic receptors.
  • Indirect-acting drugs inhibit acetylcholinesterase, increasing the amount of acetylcholine at the synapse.
  • Clinically used cholinergic agonists include choline esters (bethanecol, carbachol, cevimeline, methacholine - diagnostic tool) and alkaloids (pilocarpine). Acetylcholine itself, however, is generally not used clinically due to its widespread effects.
  • Bethanecol: a synthetic ester, selective for the GI tract and urinary bladder, with a longer duration of action than acetylcholine, and doesn't cross the blood-brain barrier. Used to treat paralytic ileus (post-surgery) and non-obstructive urinary retention.
  • Pilocarpine: a plant alkaloid, targets exocrine glands (primarily M3) and the eye, and crosses the blood-brain barrier. Used for xerostomia (dry mouth), related to head and neck radiation or Sjögren's syndrome, and glaucoma (eye drops).
  • Cevimeline: a more selective muscarinic agonist, primarily acting on M3 receptors in exocrine glands. Used to treat symptoms of dry mouth in Sjögren's syndrome.
  • Carbachol is a direct acting cholinomimetic drug used as a miotic agent (pupil constriction) and in treating glaucoma.
  • Adverse effects of muscarinic agonists can include overdosage, miosis, bradycardia, arrhythmias, hypotension and bronchoconstriction.
  • Anticholinesterases: (indirect-acting) increase acetylcholine levels by inhibiting the enzyme acetylcholinesterase used in treatment for myasthenia gravis. There are reversible and irreversible types with different durations of action.
  • Irreversible anticholinesterases, like organophosphates, include nerve agents (e.g. Sarin, VX) and insecticides, and can result in more serious effects, like respiratory and cardiac failure. Their effects are often long-lasting due to their irreversible nature.
  • Treatment for organophosphate toxicity involves atropine (muscarinic antagonist) and cholinesterase reactivators to regenerate the inhibited enzyme; especially if given before the aging process of the organophosphate occurs.

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Lecture Note_Cholinergic Agonists PDF

Description

Explore the key concepts of cholinergic agonists, their mechanisms of action, and therapeutic applications. This quiz covers direct-acting and indirect-acting agents, along with major drug groups like choline esters and alkaloids. Assess your understanding of how these agents affect the parasympathetic nervous system.

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