N+V and antiemetics Flashcards
When does vomiting occur
when vomiting centre in brain activated by input from the chemoreceptor trigger zone
When are antiemetics given
generally only when cause of vomiting known because otherwise they can delay diagnosis, esp in children
how do anti emetics work
by blocking receptors in CTZ, chosen according to the aetiology of the vomiting
metoclopramide - MOA
dopamine receptor antagonist
activity closely resembles phenothiazines
acts directly on gastric smooth muscle, simulating gastric emptying
thus may be superior to phenothiazines for emesis associated with GI and biliary disease
which one for emesis associated with GI and biliary disease and why?
metoclopramide because it acts directly on gastric smooth muscle and stimulates gastric emptying
what is the antiemetic of choice in PD and why
domperidone because it does not cross BBB so is less likely to cause central effects e.g. sedation and dystonic reactions
use low dose in PD to treat nausea caused by dopaminergic drugs
MOA domperidone
acts at CRZ and is a dopamine antagonist that does NOT cross BBB
phenothiazine antipsychotics how do they work
centrally at CTZ and are dopamine antagonists
severe dystonic reactions can sometimes occur, esp in children
antihistamines MOA
e.g. cinnarizine, cyclizine, promethazine
they are dopamine antagonists
duration of action and antimuscarinic effects will differ between which one is used
which antihistamine is the most effective in motion sickness
hyoscine hydrobromide
hyoscine hydrobromide or butylbormide - which is most effective in motion sickness
hydrobromide
this antiemetic closely resembles the action of phenothiazines
metoclopramide
name the 3 5-HT3 receptor antagonists for chemotherapy or post op n+v
granisetron, ondansetron, palonosetron
this CC has antiemetic effects and is used in the management of cancer chemo, post op, and can be used alone or in combination with other antiemetics
dexamethasone
nabilone is a synthetic cannabinoid. discuss its use as an antiemetic
used in chemo n+v that is unresponsive to other anti emetics
consider as add on treatment for chemo induced n+v that is unresponsive to optimised conventional antiemetics
NK1R antagonists e.g. aprepitant, fosprepitant and rolapritant are used to prevent chemo therapy associated n+v. they are usually given in combination with ….
dexamethasone + 5HT3 antagonist e.g. ondansetron, polonoserton, granisetron
does metoclopramide have a pro kinetic effect (promotes movement)
yes. acts directly on gut to promote gastric emptying.
thus useful in gasproduodenal, hepatic and biliary disease
restrictions to use - metoclopramide MHRA due to risk of neurological adverse effects
- in adults 18 and above only use for prevention of PONV, radio-therapy induced NV, delayed (but not acute) chemo induced NV, symptomatic treatment of NV, including that associated with acute migraine (where it may also be used to improve absorption of oral analgesics)
- max 5 days
- does not apply to unlicensed uses e.g. palliative care
metoclopramide dose
10mg TDS
max daily dose 500mcg/kg
CI metoclopramide
3–4 days after gastrointestinal surgery; epilepsy; gastro-intestinal haemorrhage; gastro-intestinal obstruction; gastro-intestinal perforation; phaeochromocytoma
true or false - acute dystonic reactions from metoclopramide are more common in young, esp girls and young females, and the elderly
true
this anti Parkinsonism drug is used to abort dystonic reactions e.g. caused by metoclopramide
procyclidine
does metoclopramide interact with antipsychotics
yes increased extrapyramidal SE
is domperidone pro kinetic
yes because it acts directly on gut to promote gastric emptying - prokinetic effect
MHRA advice on domperidone - lack of efficacy in children and reminder of CI in adults and teens
- ineffective in people under 12 or under 35kg
- max duration of treatment should not usually exceed 1 week
- risk of cardiac effects e.g. arrhythmia, it prolongs QT interval
CI for domperidone
Cardiac disease; conditions where cardiac conduction is, or could be, impaired; gastro-intestinal haemorrhage; gastro-intestinal mechanical obstruction; gastro-intestinal mechanical perforation; if increased gastro-intestinal motility harmful; prolactinoma
interactions with domperidone
Potent CYP3A4 inhibitor e.g. amiodarone, ketoconazole, erythromycin
Drugs causing QT prolong e.g. amiodarone, SSRIs, quinolone
Important interactions of 5HT2R antagonists (e.g. ondansetron) are to do with the following (3)
increased risk of serotonin syndrome
increased risk of TDP with HYPOkalaemia
increased risk of QT interval prolongations
what are dystonic reactions/dystonia
Dystonia is a neurological movement disorder. People with dystonia experience involuntary muscle spasms and contractions. Movements are often repetitive and cause unusual, awkward and sometimes painful postures
