Anti-emetics Flashcards
what are the different classes of anti-emetics
H1 receptor antagonists
D2 receptor antagonists
5HT3 receptor antagonists
Antimuscarinics
Antipsychotics
- phenothiazines
- butyriphenone
most common SE of H1 receptor antagonists
drowsiness
which is the least sedating H1 receptor antgaonist
Cyclizine
side effects H1 receptor antagonists
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
what pts should avoid H1 receptor antagonists
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
patient safety, what do you need to consider when prescribing h1 receptor antgaonist
driving
?too sedated to drive
interactions H1 receptor antagonists
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
what types of causes of n&V are d2 antagonists useful for?
They are effective in N&v due to CTZ stimulation (e.g. drugs) AND reduced gut motility e.g.
opiods or diabetic gastro paresis)
most common SE D2 antgaonists
Diarrhoea
diff between metoclopramide and domperidone
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
who should avoid prokinetics
EPSE are more common in children + young adults so avoid in this group. As pro kinetic - contraindicated in al obstruction + perforation
ppl taking antimuscarinics
what drugs should you not give concurrently with prokinetics
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.
when is ondansetron used
nausea and vomiting, particularly in the context of general anaesthesia and chemotherapy
what should you check before prescribing ondansetron
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
risk pregancy ondansetron
risk of cleft lip/palate if used in first trimester of pregnancy
anti-emetic choice pregancy
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
what are Phenothiazines
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
how do phenothiazines work
block D2 in CTZ and gut. Also block H2 and Ach in vomiting centre and vestibular system.
adverse effects phenothiazines
drowsiness, postural hypotension, EPSE eg acute dystonia (due to D2 blocking), prolong QT interval
who should avoid phenothiazines
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
interactions phenothiazines
use BNF as lots, avoid with drugs that prolong QT eg other antipsychotics, amiodarone, ciprofloxacin, macrolides, quinine, SSRIs
Butyrophenone antipsychotics
exmple?
Haloperidol
what is haloperidol particualrly used for
Used in chemical causes of nausea & vomiting (N&V) e.g. opioids
adverse effects haloperidol
extrapyramidal symptoms, sedation, QT-prolongation, Depression. At the low dose required for N&V, it causes few SE
name antimuscarinics used in palliative care? uses?
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.
how do antimuscarinics work antiemetic
bind to muscarinic receptors antagonistically- block effect of parasympathetic rest and digest
adverse effect of hyoscines
anticholinergic side effects : dry mouth, tachycardia, urinary retention, blurred vision, confusion, drowsiness
what pts shouldnt have antimuscarinics
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
Difference between hyoscine hydrobromide and hyoscine butylbromide
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.
how does dexamethasone work as an antiemetic
the inhibition of prostaglandin synthesis, by showing anti-inflammatory efficacy and by causing a decrease in the release of endogenous opiates
what is safe bet for antiemetic choices when you’re not sure
- cyclizine (can cause fluid retention)
- metoclopramide if heart failure
- ondansetron if nauseated still
