Anti-emetics

Question 1

what are the different classes of anti-emetics

Answer 1

H1 receptor antagonists

D2 receptor antagonists

5HT3 receptor antagonists

Antimuscarinics

Antipsychotics
- phenothiazines
- butyriphenone

Question 2

most common SE of H1 receptor antagonists

Answer 2

drowsiness

Question 3

which is the least sedating H1 receptor antgaonist

Answer 3

Cyclizine

Question 4

side effects H1 receptor antagonists

Answer 4

most common-drowsiness. Cyclizine is the least sedating. Due to anticholinergic effects they may cause dry mouth + throat (may be useful in Pts with oral secretions. After IV inj - may cause transient tachycardia + palpitations

Question 5

what pts should avoid H1 receptor antagonists

Answer 5

avoid in pts at risk of hepatic encephalopathy due to sedating effect. Also should be avoided in pts susceptible to anticholinergic effects e.g. prostatic hypertrophy (who may develop urinary retention

Question 6

patient safety, what do you need to consider when prescribing h1 receptor antgaonist

Answer 6

driving

?too sedated to drive

Question 7

interactions H1 receptor antagonists

Answer 7

sedation may be greater when combined with other sedating drugs e.g. benzodiazepines, opioids.
Anticholinergic effects may be greater in pts taking ipratropium or tiotropium

Question 8

what types of causes of n&V are d2 antagonists useful for?

Answer 8

They are effective in N&v due to CTZ stimulation (e.g. drugs) AND reduced gut motility e.g.
opiods or diabetic gastro paresis)

Question 9

most common SE D2 antgaonists

Answer 9

Diarrhoea

Question 10

diff between metoclopramide and domperidone

Answer 10

metoclopramide can induce extrapyramidal side effects via the same mechanisms as antipsychotics. e.g. acute dystonia reaction. and hyperprolactinaemia. Domperidone tends not to cause EPSE as it doesn’t cross the blood brain barrier

Question 11

who should avoid prokinetics

Answer 11

EPSE are more common in children + young adults so avoid in this group. As pro kinetic - contraindicated in al obstruction + perforation

ppl taking antimuscarinics

Question 12

what drugs should you not give concurrently with prokinetics

Answer 12

Do not give prokinetics concurrently with drugs with antimuscarinic activity (for example cyclizine and hyoscine).

stops them working properly (doing opposite things)

antimuscarinic drugs competitively block the action of prokinetics.

Question 13

when is ondansetron used

Answer 13

nausea and vomiting, particularly in the context of general anaesthesia and chemotherapy

Question 14

what should you check before prescribing ondansetron

Answer 14

if prolonged QT or on drugs that prolong QT

as ondansetron can prolong the QT interval although usually only evident at high doses eg >16mg ondansetron. Avoid in pts with prolonged QT, if in doubt, ECG before prescribing

Question 15

risk pregancy ondansetron

Answer 15

risk of cleft lip/palate if used in first trimester of pregnancy

Question 16

anti-emetic choice pregancy

Answer 16

first line
- antihistamines: oral cyclizine or promethazine
- phenothiazines: oral prochlorperazine or chlorpromazine

second line
- oral ondansetron: ondansetron during the first trimester is associated with a small increased risk of the baby having a cleft lip/palate.
- oral metoclopramide or domperidone: metoclopramide may cause extrapyramidal side effects. It should therefore not be used for more than 5 days

Question 17

what are Phenothiazines

Answer 17

Examples: prochlorperazine, chlorpromazine

Indications:
Nausea and vomiting, particularly if due to vertigo, however due to SE profile other classes used first
Psychotic disorders where they are used as a first generation (typical) antipsychotic

Question 18

how do phenothiazines work

Answer 18

block D2 in CTZ and gut. Also block H2 and Ach in vomiting centre and vestibular system.

Question 19

adverse effects phenothiazines

Answer 19

drowsiness, postural hypotension, EPSE eg acute dystonia (due to D2 blocking), prolong QT interval

Question 20

who should avoid phenothiazines

Answer 20

can cause hepatotoxicity and drowsiness = avoid in severe liver disease, avoid in pts susceptible to anticholinergic SE such as ppl w prostatic hypertrophy - may cause urinary retention

Question 21

interactions phenothiazines

Answer 21

use BNF as lots, avoid with drugs that prolong QT eg other antipsychotics, amiodarone, ciprofloxacin, macrolides, quinine, SSRIs

Question 22

Butyrophenone antipsychotics
exmple?

Answer 22

Haloperidol

Question 23

what is haloperidol particualrly used for

Answer 23

Used in chemical causes of nausea & vomiting (N&V) e.g. opioids

Question 24

adverse effects haloperidol

Answer 24

extrapyramidal symptoms, sedation, QT-prolongation, Depression. At the low dose required for N&V, it causes few SE

Question 25

name antimuscarinics used in palliative care? uses?

Answer 25

Hyoscine hydrobromide and hyoscine butylbromide

Palliative care uses: antiemetic and reducing copious respiratory secretions
Other uses:BUSCOPAN is the trade name for “hyoscine butylbromide”. This belongs to a group of medicines called “antispasmodics” - used in IBS.

Question 26

how do antimuscarinics work antiemetic

Answer 26

bind to muscarinic receptors antagonistically- block effect of parasympathetic rest and digest

Question 27

adverse effect of hyoscines

Answer 27

anticholinergic side effects : dry mouth, tachycardia, urinary retention, blurred vision, confusion, drowsiness

Question 28

what pts shouldnt have antimuscarinics

Answer 28

use with caution in pts with ?acute angle glaucoma - can ppt a dangerous increase in intraocular pressure. Avoid in pts at risk of arrhythmias, unless indication for use is bradycardia

Question 29

Difference between hyoscine hydrobromide and hyoscine butylbromide

Answer 29

Unlike hyoscine hydrobromide, hyoscine butylbromide does not cross the blood-brain barrier and therefore does not cause drowsiness or have a central anti-emetic action.

Question 30

how does dexamethasone work as an antiemetic

Answer 30

the inhibition of prostaglandin synthesis, by showing anti-inflammatory efficacy and by causing a decrease in the release of endogenous opiates

Question 31

what is safe bet for antiemetic choices when you’re not sure

Answer 31

1. cyclizine (can cause fluid retention)
2. metoclopramide if heart failure
3. ondansetron if nauseated still