Anti-Nausea Flashcards
How is nausea triggered?
Triggered by:
- sensory afferents from via the midbrain (eg. when you see something gross)
- vestibular nuclei (eg. imbalance)
- direct triggers (eg. drugs)
- visceral afferents from gut
They all act on the chemoreceptor trigger zone to cause nausea. (CTZ)
What are 2 drugs that work on the vestibular nuclei? What kind of drugs are they?
Hyoscine hydrobromide (muscarinic ACh receptor antagonist)
and cyclizine (H1 receptor antagonist from vestibular system to CTZ)
What are the indications and side effects of hyoscine hydrobromide
Indications:
- motion sickness
- bowel obstruction
- don’t like tablets
SE:
- sedation
- glaucoma
- dry mouth and constipation
- memory problems
What are the indications and side effects of cyclizine
Indications:
- motion sickness
- morning sickness (promethazine usually used)
SE:
- sedation
- excitation
- antimuscarinic = dry mouth, constipation, urinary retention
- cardiac toxicity (long QT)
What are two drugs that act on the visceral afferents in the gut and what are their mechanisms?
Ondansetron (5HT3 receptor antagonists. serotonin is parasympathetic and increases contractions in the gut.)
Metacloperamide (D2 receptor antagonists)
How does ondansetron work and what are its SE?
- reduces GI motility
- reduces GI secretions
SE: (uncommon)
- constipation
- headache
- elevated LFTs
- long QT
How does metacloperamide work?
increases ACh at muscarinic receptors in the gut
promotes gastric emptying by :
- increasing tone at LOSphincter so it closes
- increasing tone of gastric contractions
- decreasing tone of pylorus so it opens
- increases peristalsis
When is metacloperamide indicated and what are its SE
Good for:
- GORD
- ileus (lack of bowel movements)
SE:
- galactorrhoea via prolactin release
- extra-pyramidal effects eg. dystonia, parkinsonism
Name 3 drugs that work on the chemoreceptor trigger zone (CTZ) and their mechanisms.
Metacloperamide, Haloperidol, etc (D2 receptor antagonist)
Dexmethasone (Corticosteroids)
Aprepitant (Neurokinin 1 receptor antagonist)
When is haloperidol indicated?
An antipsychotic.
Chemotherapy and palliation
When is dexmethasone indicated and what are some SE?
- perioperative nausea
- chemo
- palliation (useful in low appetite)
SE:
- insomnia
- increased appetite and blood sugar
When is apprepitant indicated and some side effects?
- increases 5HT3 receptor antagonists effects
- has anxiolytic and antidepressant properties
- good for chemo eg. delayed emesis
SE:
- headache
- diarrhoea/constipation
- Steven-Johnson syndrome
