Anti-emetics (H1 receptor antagonists, dopamine antagonists and 5HT3 receptor antagonists)

Question 1

Name examples of H1 receptor antagonists/antihistamines.

Answer 1

cyclizine, promethazine, cinnarizine

Question 2

What are the indications of H1 receptor antagonists/antihistamines?

Answer 2

nausea, vomiting, vertigo, motion sickness, labyrinthine disorders, nausea and vomiting/relief of symptoms associated with vestibular disorders and palliative care.

Question 3

What are the contraindications of H1 receptor antagonists?

Answer 3

acute porphyrias

Question 4

What is the mechanism of action of H1 receptor antagonists?

Answer 4

Antihistamines’ antiemetic mechanism of action is not fully understood. However it is thought likely that they act on receptors in the vestibular system and vomiting centre of the medulla oblongata, such as the 5-hydroxytyptamine and muscarinic receptors.

Question 5

What are the very common/common unwanted side effects of H1 receptor antagonists?

Answer 5

drowsiness, sedation

Question 6

What is the patient/carer advice for H1 receptor antagonists?

Answer 6

Advise patients of effects of drowsiness on driving, skilled tasks, operating machinery etc. Also that they enhance the effects of alcohol.

Question 7

Name examples of dopamine antagonists.

Answer 7

domperidone, droperidol, metoclopramide, prochlorperazine.

Question 8

What are the indications of dopamine antagonists?

Answer 8

relief of nausea and vomiting, prevention and treatment of postoperative nausea and vomiting, prevention of nausea and vomiting caused by opioid analgesics in post-operative PCA, nausea and vomiting associated with migraine/radiotherapy/chemotherapy/palliative care, (metoclopramide), GI pain in palliative care (domperidone), prevention of nausea and vomiting (prochlorperazine), labyrinthine disorders (prochlorperazine), nausea and vomiting in previously diagnosed migraine (prochlorperazine).

Question 9

What are the contraindications of dopamine antagonists?

Answer 9

CNS depression, comatose states, phaeochromocytoma, cardiac disease (domperidone), conditions where cardiac conduction is/could be impaired (domperidone), GI haemorrhage, if increased GI motility is harmful (domperidone), GI obstruction/perforation, prolactinoma (domperidone), 3-4 days after GI surgery (metoclopramide), bradycardia (droperidol), hypokalaemia (droperidol), hypomagnesaemia (droperidol), QT-interval prolongation (droperidol).

Question 10

What is the mechanism of action of dopamine antagonists?

Answer 10

Dopamine antagonists block the dopamine receptors in the chemoreceptor trigger zone. This means that the vomiting centre in the oblongata medulla, that is responsible for triggering nausea and vomiting, does not receive stimulating signals and so nausea and vomiting is reduced.

Question 11

What are the common/very common side effects of dopamine antagonists?

Answer 11

drowsiness, dry mouth, malaise, extrapyramidal effects, galactorrhoea, gynaecomastia, hyperprolactinaemia, hypotension, menstrual changes.

Question 12

What are the monitoring requirements of droperidol?

Answer 12

Continuous pulse oximetry for 30 mins post-administration if there is a risk of ventricular arrhythmia.

Question 13

What is the patient/carer advice of dopamine antagonists?

Answer 13

Advise patients how to administer buccal tablets. Patients/carers should be told how to recognise signs/symptoms of arrhythmia such as palpitations and syncope and to seek medical attention if this develops (domperidone). Counselling on use of pipette with oral solution.

Question 14

Name examples of 5HT3 receptor antagonists.

Answer 14

granisetron, ondansetron, palonosetron

Question 15

What are the indications of 5HT3 receptor antagonists?

Answer 15

nausea and vomiting induced by chemotherapy, prevention/treatment of postoperative nausea and vomiting.

Question 16

What are the contraindications of ondansetron?

Answer 16

congenital long QT syndrome

Question 17

State the mechanism of action of 5HT3 receptor antagonists.

Answer 17

Serotonin (5HT3) is part of the chemotrigger zone that is responsible for sending signals to the vomiting centre if activated by toxins. When activated, the CTZ activates the vomiting centre of the medulla oblongata and triggers vomiting. 5HT3 receptor antagonists block 5HT3 (serotonin) receptors in the GI tract and CNS and inhibit this process.

Question 18

What are the common/very common side effects of 5HT3 receptor antagonists?

Answer 18

constipation, diarrhoea, dizziness, flushing, headache, injection site reactions, insomnia.

Question 19

What is the patient/carer advice for 5HT3 receptor antagonists?

Answer 19

Advise patients to not expose site of the patch to sunlight during use and for 10 days after removal with transdermal use (granisetron). Advise patients how to administer orodispersible films and lypophilisates (ondansetron). Advise of effects of dizziness/drowsiness on driving/skilled/tasks/operating machinery etc.