5. Nausea and labyrinth disorders

Question 1

List of antiemetics

Answer 1

Dopamine-receptor antagonist
domperidone
metoclopramide

Antihistamines
cinnarizine
cyclizine
promethazine

5-HT3 receptor antagonist
ondansetron

Antimuscarinic
hyoscine

Antipsychotics
Prochlorperazine
Droperidol
Haloperidol

Chemoreceptor trigger zone is outside the blood brain barrier

Question 2

Antiemetics and pregnancy

Answer 2

Morning sickness usually common in 1st trimester. Recommend rest, change diet, drink fluids.

If symptoms persist:
antiemetic should be offered e.g promethazine, metoclopramide, prochlorperazine

Switch to a different class, if symptoms last longer than 24 hrs.
Seek specialist opinion, if symptoms last longer than 48 hours.

Question 3

Treatment of post-operative nausea and vomiting

Answer 3

antiemetic combination therapy

combination of 2 or more antiemetics from different drug classes;

• dexamethasone
• domperidone
• prochlorperazine, droperdol, haloperido
• cyclizine

Question 4

Before operation, an assesement is conducted for those at high risk for post-operative nausea and vomiting. Who are those groups?

Answer 4

• Female
• Non-smoker
• History
• Motion sickness
• Opioids
• Anaesthetic
• Surgery type
• Surgery Duration

Question 5

Metoclopramide mechanism of action

Answer 5

A dopamine receptor antagonist and blocks D2 receptors in the chemoreceptor trigger zone.
Blocks dopamine receptors in the gut and promotes gastric emptying

Question 6

Metoclopramide dose

Answer 6

10mg TDS for 5 days
Licensed for 18 years+

Question 7

metoclopramide side effects

Answer 7

Acute dystonic reactions
- uncontrolled movements in the face, skeletal muscles and eyes
Metoclopramide enters the brain to cause this side effect

Common in young females/elderly

As metoclopramide blocks D2 receptors in the brain which regulates movem

As metoclopramide blocks D2 receptors in the brain which regulates movement. The same happens for antipsychotics.

Question 8

Metoclopramide interactions

Answer 8

Increased risk of extrapyramidal symptoms if taken at the same time as antipsychotics

Metoclopramide should never ben given to a patient with Parkinson’s disease, as this antagonises their treatment.

Question 9

Domperidone mechanism of action

Answer 9

works similarly to metoclopramide. It blocks dopamine-2, dopamine-3 receptors in the chemoreceptor trigger zone and in the gut

Question 10

Domperidone and parkinson’s disease

Answer 10

Domperidone can be used in parkinson’s disease, as it does not cause extrapyrimidal symptoms due it not entering the brain

Question 11

Domperidone dose

Answer 11

10mg TDS for 1 weeks
Licensed for 12 years

Lack of efficacy in those less than 12 years or those who weigh less than 35kg

Question 12

Domperidone side effects

Answer 12

Can prolong QT interval.
Patients must report signs of fainting, palpitations.

Question 13

Domperidone interactions

Answer 13

Interacts with drugs that also prolong the QT interval –> arrhythmias
Antipsychotic, anti-arrhythmic drugs, citalopram, escitalopram, clarithromycin, erythromycin, hydroxyzine, lithium, methadone, quinolones, onadensetron

Domperidone is metabolised by CYP3A4 enzymes. Therefore it interacts with CYP3Z4 inhibitors:
amiodarone, azole antinfungals: fluconaozle, ketoconazole, clarithromycin, erythromycin, diltiazem and verapamil

Question 14

5-HT3 receptor antagonists mechanism of action

Answer 14

Blocks 5-HT3 receptors in the chemoreceptor trigger zone and GI tract

Question 15

5-HT3 receptor antagonists side effect

Answer 15

Prolonged QT interval

Question 16

5-HT3 receptor antagonists and pregnancy

Answer 16

Teratogenic
Increased risk of cleft lip, when used in the first trimester

Question 17

5-HT3 receptor antagonists interactions

Answer 17

Interacts with drugs that also prolong the QT interval = arrhythmias
Antipsychotic, anti-arrhythmic drugs (amiodarone, sotalol) clomipramine, citalopram, escitalopram, clarithromycin, erythromcyin, domperidone, hydroxzine, lithoum, methadone, quinolones

Hypokalaemia increases the risk of a prolonged QT interval, therefore domperidone interacts with drugs that cause hypokalaemia:
beta agonists, corticosteroids, loop and thiazide diuretics, theophylline

Hypokalaemic drugs taken with drugs that prolong QT interval = increases risk of torsades de pointes

5-HT3 drugs are serotonergic (even tho they are antagonist, no clear reason)
Interacts with drugs that also increase serotonin = increasing risk of serotonin syndrome
antidepressants (TCA’s SSRI’s MAOI), amfetamine, lithium, MAO-B inhibitor, methadone, ST john’s wort, tramadol 5-HT1 agonists e.g sumatriptan