Drugs, Emesis, & Gastric Motility
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Questions and Answers

What is the primary mechanism of action of hyoscine in preventing motion sickness?

  • Histamine H1 antagonism
  • Dopamine receptor antagonism
  • Calcium channel antagonism
  • Muscarinic cholinergic antagonism (correct)

Which of the following is a common side effect of antihistamines used to treat motion sickness?

  • Dry mouth
  • Blurred vision
  • Drowsiness (correct)
  • All of the above

What is the function of hyoscine hydrobromide in preventing motion sickness?

  • To treat established symptoms of motion sickness
  • To inhibit vomiting (correct)
  • To reduce sedation
  • To prevent stomach irritants

Which of the following is NOT a form of hyoscine?

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

What is the primary advantage of using hyoscine over antihistamines in preventing motion sickness?

<p>Sedation is less of a problem with hyoscine (D)</p> Signup and view all the answers

Which of the following is a therapeutic use of promethazine?

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

What is the additional mechanism of action of cinnarizine besides being an antihistamine?

<p>Calcium channel block (C)</p> Signup and view all the answers

What is the form of hyoscine used to prevent motion sickness?

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

What is the mechanism of action of phenothiazines as antiemetics?

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

Which of the following dopamine antagonists does not cross the blood-brain barrier?

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

What is the site of action of ondansetron in the peripheral circulation?

<p>Visceral afferent fibers (B)</p> Signup and view all the answers

What is a common adverse effect of 5-HT3 antagonists such as ondansetron?

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

Which of the following is NOT a therapeutic use of 5-HT3 antagonists?

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

What is the advantage of domperidone over metoclopramide?

<p>Fewer CNS adverse effects (D)</p> Signup and view all the answers

What is the mechanism of dopamine antagonists in reducing nausea and vomiting?

<p>Blockade of the dopamine receptor involved in the vomiting reflex (C)</p> Signup and view all the answers

Which of the following is a pharmacological class that has been developed specifically for the treatment of nausea and vomiting?

<p>5-HT3 antagonists (B)</p> Signup and view all the answers

What is the primary location of the vomiting centre?

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

Which of the following neurotransmitters is NOT involved in the transmission of vestibular stimuli?

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

What is the name of the receptor antagonists that have been introduced as a major advance in the treatment of nausea and vomiting?

<p>5HT3 receptor antagonists (B)</p> Signup and view all the answers

Which of the following antiemetic drugs is used to treat motion sickness?

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

What is the class of substance P, an 11 amino acid peptide?

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

Why is the chemoreceptor trigger zone (CTZ) an important location for anti-emetic drug access?

<p>It is outside the blood-brain barrier (B)</p> Signup and view all the answers

What is a common unwanted effect of cholinergic muscarinic antagonists, such as hyoscine?

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

Which of the following antiemetic drugs does not involve antagonism of neurotransmitter receptors?

<p>None of the above (D)</p> Signup and view all the answers

Flashcards

Hyoscine

A type of motion sickness medication that works by blocking the cholinergic system, specifically the muscarinic receptors. It is effective in preventing travel sickness.

Hyoscine Patch

A medication used to target motion sickness, categorized as a muscarinic cholinergic antagonist. It is available in both tablet and patch forms, with the patches being placed behind the ear for absorption.

Hyoscine Hydrobromide

A specific form of hyoscine known for its high lipid solubility. It is commonly used to inhibit vomiting at lower doses compared to its other form.

Hyoscine Butylbromide

A form of hyoscine that is less lipid-soluble compared to hyoscine hydrobromide. It has different mechanisms of action and is not primarily used for vomiting.

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Anticholinergic Side Effects of Hyoscine

Side effects associated with hyoscine, which include dryness of the mouth and blurred vision. Sedation is less pronounced compared to antihistamines.

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Histamine (H1) Antagonists

A medication used to treat motion sickness by blocking the effects of histamine. They also have additional mechanisms of action, such as calcium channel block and muscarinic antagonism.

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Common Antihistamines as Antiemetics

Antihistamines commonly used as antiemetics, which include cinnarizine, cyclizine, and promethazine. They have several mechanisms of action, including calcium channel block and muscarinic antagonism.

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Drowsiness and Sedation from Antihistamines

A potential side effect of antihistamine use, which may include drowsiness and sedation.

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Phenothiazines

A class of drugs that were introduced in the 1950s. They act as dopamine antagonists and may also have activity at other neurotransmitter receptors, but can lead to movement disorders.

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Dopamine Antagonists

Drugs that block the effects of dopamine, specifically the D2 receptor subtype. These are used to manage nausea and vomiting by interfering with the vomiting reflex.

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Metoclopramide

A selective dopamine antagonist used to manage nausea and vomiting. It has specific action on the D2 receptor subtype involved in the vomiting reflex.

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Domperidone

A dopamine antagonist that primarily acts on the D2 receptor subtype involved in nausea and vomiting. Unlike many other dopamine antagonists, it does not cross the blood-brain barrier.

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5-Hydroxytryptamine (5-HT3) Antagonists

A class of drugs that block the activity of 5-hydroxytryptamine (5-HT), also known as serotonin. They have both peripheral and central mechanisms of action.

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Ondansetron

A specific 5-HT3 antagonist that blocks the effects of serotonin on peripheral visceral afferent fibers and centrally on the chemoreceptor trigger zone.

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Therapeutic Uses of Ondansetron

The use of ondansetron to manage vomiting associated with surgery, radiation therapy, and chemotherapy.

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Adverse Effects of Ondansetron

Potential side effects associated with the use of ondansetron, which include constipation, headache, and flushing.

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Vomiting Centre

The area of the brain that is responsible for triggering vomiting, often targeted by anti-emetic drugs.

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Chemoreceptor Trigger Zone

A specific area located outside the blood-brain barrier responsible for detecting toxins and triggering the vomiting reflex. It is directly accessible to certain drugs.

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GI Tract

The gastrointestinal tract, which is a target site for anti-emetic drugs. It is involved in various stages of the nausea and vomiting process.

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Antiemetic Drugs

Medications designed to reduce or prevent nausea and vomiting. They act by targeting specific neurotransmitter receptors in various areas of the body.

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Significance of 5-HT3 Receptor Antagonists

The development of 5-HT3 receptor antagonists marked a significant advancement in the treatment of nausea and vomiting, particularly for cases related to chemotherapy and surgery.

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Five Groups of Antiemetic Drugs

The 5 main categories of anti-emetic drugs, all of which involve blocking the activity of neurotransmitter receptors.

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Study Notes

Motion Sickness Treatment

  • Scopolamine's comparative effectiveness with other agents like antihistamines and calcium channel antagonists is unknown due to a lack of randomized controlled trials.
  • Hyoscine, a muscarinic cholinergic antagonist, is an effective preventive measure for travel sickness and is available in tablet and patch forms, with the patches placed behind the ear.

Hyoscine

  • Two major forms of hyoscine exist: hyoscine hydrobromide, which is more lipid-soluble and used to inhibit vomiting at lower doses, and hyoscine butylbromide.
  • Anticholinergic side effects of hyoscine include dry mouth and blurred vision, but sedation is less of a problem compared to antihistamines.

Histamine (H1) Antagonists

  • Commonly used antihistamines as antiemetics include cinnarizine, cyclizine, and promethazine, which also have additional mechanisms of action, such as calcium channel block and muscarinic antagonism.
  • These drugs may induce drowsiness and sedation as adverse effects.
  • Phenothiazines, introduced in the 1950s, act as dopamine antagonists and may also be histamine (H1) and cholinergic (M) antagonists, but can cause movement disorders like tardive dyskinesia.

Dopamine Antagonists

  • Metoclopramide and domperidone are more selective dopamine antagonists, acting on the D2 receptor subtype involved in the vomiting reflex.
  • Domperidone does not cross the blood-brain barrier, resulting in fewer CNS adverse effects.

5-Hydroxytryptamine (5-HT3) Antagonists

  • Ondansetron blocks the effect of 5-HT on visceral afferent fibers peripherally and on the chemoreceptor trigger zone centrally.
  • Therapeutic uses include post-operative and radiotherapy-induced vomiting, as well as vomiting caused by cytotoxic drugs like cisplatin.
  • Adverse effects of ondansetron include constipation, headache, and flushing.

Antiemetics Overview

  • Anti-emetic drugs work at three potential sites: the vomiting centre, the chemoreceptor trigger zone, and the GI tract.
  • These drugs can be divided into five groups, all of which involve antagonism of neurotransmitter receptors.
  • The chemoreceptor trigger zone is outside the blood-brain barrier, making it accessible to certain drugs.
  • The introduction of 5-HT3 receptor antagonists was a significant advance in the development of anti-emetic drugs.

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GI Tract 1 Powerpoint Lecture.pptx

Description

This quiz covers the prevention and treatment of motion sickness, including the effectiveness of scopolamine and other agents. It discusses the use of hyoscine, a muscarinic cholinergic antagonist, in preventing travel sickness.

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