Anti-emetics Flashcards
What is emesis?
An emetic is an agent that causes vomiting.
Stages of emesis are nausea, retching and vomiting.
What causes emesis?
Disease states- migraine, bacterial and viral infections.
Physiological status- pregnancy.
Unwanted side effects- CINV and PONV, opioids.
What are the components of the vomiting reflux?
Regulated in the medulla.
The Chemoreceptor trigger zone. This is the main site of action for antiemetic drugs.
Vagal pathway (sensory input)
Vestibular pathway (affected by disorientated motions).
What are the actions of antiemetics?
Neurotransmitter antagonists- block neurotransmitters preventing triggering of emetic response.
List the different anti-emetics that block neurotransmitter release. (6)
5HT3 block serotonin H1 block histamine M block ACH D2 blocks dopamine NK1 blocks substance P. Enkephalin.
What are the most commonly used anti-emetic drugs?
5HT3- Serotonin
M- ACH
H- Histamine.
What anti-emetic target the vomiting centre?
M
H
NK1
5HT3
What anti-emetics block the vestibular pathway?
M
H1
What anti-emetics block the vagal pathway?
5HT3
What antiemetic blocks the chemoreceptor trigger zone?
D2
5HT3
NK1
What are the actions of H1 antagonists?
They target the vestibular pathway. Are used to treat motion sickness, vestibular disease and GI irritants.
The side effects include drowsiness and sedation.
What are examples of H1 antagonists
Cyclizine- used to treat motion sickness.
Cinnarizine- Morning sickness.
What are the actions of H3 agonists?
Activate H-receptors in the blood vessels of the inner ear.
Reverses the underlying problems of endolymphatic hydrops causing vasodilator and increased permeability.
What are the side effects of H3 agonists?
GI disturbances, headache, rash, pruritus.
What are examples of H3 agonists?
Betahistamine
Hydrochloride (anti-vertigo drug).
Explain anti-emetic Muscuarinic receptor (ACH) antagonists.
A good general purpose drug due to its non selective features
The drug of choice for motion sickness.
Targets vestibular pathway
What are the side effects of muscuarinic receptor antagonists
Dry mouth and blurred vision- however less sedative effects than histamine antagonists.
What are examples of anti-emetic ACH drugs?
Hyscoine and scopolamine.
Explain D2 receptor antagonists
Strong representation in the CTZ.
Most powerful anti-emetic drug.
Used to treat uraemia, opiod induced emesis, CINV, GI disorders and viral gastroentritis.
What are phenothiazamines?
D2 receptor antagonists that are the drug of choice for morning sickness.
Side effects include sedation, hypotension, dystonia, dyskineasia.
What is metoclopramide?
D2 receptor antagonist.
Penetrated blood barrier.
Acts on GIT to increase gut motility.
Side effects include movement disorders, spasmodic torticolitis and menstrual disturbances.
What is domperidone?
D2 receptor antagonist.
Does not penetrate blood barrier so therefore has less central effectiveness however has fewer side effects.
Used to treat migraines, CINV and sickness due to emergency contraception.
What are anti-emetic serotonin receptor antagonists?
Work on the vagal, CTZ and vomiting centre.
Used to treat CINV and PONV and radiation induced vomiting.
What is ondansteron?
5HT3 antagonist. Drug of choice for CINV and PONV. Side effects include headache and GI disturbances. Strands of drug end in steron. Granisteron Palonosteron.
What are NK1 antagonists?
They become active at the late phase of emesis with cytotoxic drugs.
Substance P antagonists that work on the CTZ and vomiting centre.
What is aprepitant?
A type of NK1 antagonist.
Used for CINV and PONV.
Strands inlcude fosaprepitant.
Drugs that end in pitant.
Explain the anti-emetic effects of cannabionoids?
Act as agonists of CB (brain stem) and CTZ.
E.g Nabilone and Marinol
Explain the steroid effects of anti-emetics.
Dexamethasone.
Used to treat CINV in conjunction with D2 or 5HT3
List some therapeutic uses of emetics
Syrup of ipecac and Apomorphine stimulate CTZ>
Where does 5HT3 target
Vomiting centre, vagal pathway, CTZ
Where do M target?
Vomiting centre, vestibular pathway
Where do NK1 target?
Vomiting centre and the CTZ
Where do D2 target?
CTZ
Where do H target?
Vestibular pathway and the vomiting centre