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What is the primary mechanism of action of hyoscine in preventing motion sickness?
What is the primary mechanism of action of hyoscine in preventing motion sickness?
Which of the following is a common side effect of antihistamines used to treat motion sickness?
Which of the following is a common side effect of antihistamines used to treat motion sickness?
What is the function of hyoscine hydrobromide in preventing motion sickness?
What is the function of hyoscine hydrobromide in preventing motion sickness?
Which of the following is NOT a form of hyoscine?
Which of the following is NOT a form of hyoscine?
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What is the primary advantage of using hyoscine over antihistamines in preventing motion sickness?
What is the primary advantage of using hyoscine over antihistamines in preventing motion sickness?
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Which of the following is a therapeutic use of promethazine?
Which of the following is a therapeutic use of promethazine?
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What is the additional mechanism of action of cinnarizine besides being an antihistamine?
What is the additional mechanism of action of cinnarizine besides being an antihistamine?
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What is the form of hyoscine used to prevent motion sickness?
What is the form of hyoscine used to prevent motion sickness?
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What is the mechanism of action of phenothiazines as antiemetics?
What is the mechanism of action of phenothiazines as antiemetics?
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Which of the following dopamine antagonists does not cross the blood-brain barrier?
Which of the following dopamine antagonists does not cross the blood-brain barrier?
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What is the site of action of ondansetron in the peripheral circulation?
What is the site of action of ondansetron in the peripheral circulation?
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What is a common adverse effect of 5-HT3 antagonists such as ondansetron?
What is a common adverse effect of 5-HT3 antagonists such as ondansetron?
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Which of the following is NOT a therapeutic use of 5-HT3 antagonists?
Which of the following is NOT a therapeutic use of 5-HT3 antagonists?
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What is the advantage of domperidone over metoclopramide?
What is the advantage of domperidone over metoclopramide?
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What is the mechanism of dopamine antagonists in reducing nausea and vomiting?
What is the mechanism of dopamine antagonists in reducing nausea and vomiting?
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Which of the following is a pharmacological class that has been developed specifically for the treatment of nausea and vomiting?
Which of the following is a pharmacological class that has been developed specifically for the treatment of nausea and vomiting?
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What is the primary location of the vomiting centre?
What is the primary location of the vomiting centre?
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Which of the following neurotransmitters is NOT involved in the transmission of vestibular stimuli?
Which of the following neurotransmitters is NOT involved in the transmission of vestibular stimuli?
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What is the name of the receptor antagonists that have been introduced as a major advance in the treatment of nausea and vomiting?
What is the name of the receptor antagonists that have been introduced as a major advance in the treatment of nausea and vomiting?
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Which of the following antiemetic drugs is used to treat motion sickness?
Which of the following antiemetic drugs is used to treat motion sickness?
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What is the class of substance P, an 11 amino acid peptide?
What is the class of substance P, an 11 amino acid peptide?
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Why is the chemoreceptor trigger zone (CTZ) an important location for anti-emetic drug access?
Why is the chemoreceptor trigger zone (CTZ) an important location for anti-emetic drug access?
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What is a common unwanted effect of cholinergic muscarinic antagonists, such as hyoscine?
What is a common unwanted effect of cholinergic muscarinic antagonists, such as hyoscine?
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Which of the following antiemetic drugs does not involve antagonism of neurotransmitter receptors?
Which of the following antiemetic drugs does not involve antagonism 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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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.
