Flashcards in Antiemetics Deck (22)
name 2 dopamine D2 receptor antaagonists
how do dopamine D2 receptor antagonists work?
domperidone = D2 receptor antagonist
Meoclopramide = D2 antagonist with antagonist activity at 5-HT3 and agonist activity at 5-HT4 receptors
what is the main difference between metocloparamide and domperidone?
domperidone doesn't cross the blood brain barrier
where are D2 receptors located and what do they do?
expressed in chemoreceptor trigger zone (CTZ) just outside of blood brain barrier
Important in detection of emetogenic substances in blood (e.g opiates)
Dopamine relaxes stomach and lower oesophageal sphincterand disrupts gastroduodenal coordination
indications for dopamine D2 receptor antagonists?
variety of nausea + vomiting (particularly where reduced gut motility)
Domperidone used in drug/chemo induced vomiting
GORD add on if no response to PPI +/- H2 receptor antagonists
side effects of dopamine D2 receptor antagonists?
metoclopramide = rarely extrapyramidal syndromes/disorders of movement
cautions for dopamine D2 receptor antagonists?
avoid is GI obstruction and perforation
metoclopramide best avoied in children/teens with common extrapyramidal effects
name 3 histamine H1 receptor antagonists
how do H1 receptor antagonists work?
competitive antagonism of H1 receptors in the vomiting centre and elsewhere in the CNS (causes sedation)
Blocks M1 Ach receptors in the vestibular apparatus (contributes to effectiveness)
indications for H1 receptor antagonists?
nausea + vomiting due to motion sickness and vertigo and post operative
side effects of H1 receptor antagonists?
drowsiness and sedation (avoid skilled tasks eg. driving)
reduced saliva/dry mouth (anti cholinergic action)
transient tachycardia if IV
cautions for H1 receptor antagonists?
avoid in prostatic hyperplasia
avoid if at risk of hepatic encephalopathy
name 2 phenothiazines
how to phenothiazines work?
competitive antagonism of dopamine D2, histamine H1 and muscarinic M1 receptors in vomiting centre, vestibular centre and peripherally in gut
indications for phenothiazines?
nausea + vomiting due to vertigo and sometimes chemo but not preferred
side effects of phenothiazines?
drowsiness and postural hypotension
extrapyramidal symptoms (same as D2)
QT interval prolongation
cautions for phenothiazines?
avoid in severe liver disease and prostatic hyperplasia
reduce dose in elderly
name a 5-HT3 receptor antagonist
how do 5-HT receptor antagonists work?
competitive antagonist of inotropic 5-HT receptors located in CTZ, NTS and peripherally on terminals of vagal afferents innervating GI tract.
CTZ senses emetogenic stimuli in blood, 5-HT released from enterochromaffin cells n the gut stimulates vagal afferents that via the NTS activate vomiting centre
indications for 5-HT3 receptor antagonists>
nausea + vomiting due to chemo and radiotherapy
post operative nausea and vomiting
side effects of 5-HT3 receptor antagonists?
diarrhoea and headaches can occur