Anti-emetics Flashcards
Define emesis.
Physical event; forceful evacuation of gastric contents through the mouth. A protective mechanism in response to something harmful being ingested.
What are the stages of emesis?
Feeling of nausea, retching, vomiting.
What can emesis be caused by?
Disease states such as migraine, bacterial and viral infections. Pregnancy, motion sickness. Side effects of drugs such as chemotherapy and post-op.
What is the vomiting reflux regulated by?
CNS (medulla). “Brainstem emetic control center”
What are the 3 inputs of the emetic control center?
The Chemorecpetor Trigger Zone, The Vagal Pathway, The Vestibular Pathway.
What is the chemoreceptor trigger zone?
Associated with substances, toxins and drugs - sensitive to chemicals. Main site of action of antiemetic drugs.
What is the vagal pathway?
Associated with sensory input (pain, smell, sight, thought). Stimuli from the pharynx and GI tract.
What is the vestibular pathway?
Disorientating motion.
List the neurotransmitters involved in the blockade during the the emesis response.
serotonin, ACh, dopamine, substance P, histamine, enkephalin.
What are H1 antagonists?
Act on vomiting centre and the vestibular pathway, act on histamine. Used in emesis caused by motion sickness, vestibular disease and Gi irritants.
Name the H1 antagonists?
Cyclizine, Cinnarizine, Promethazine
What are the side effects of H1 antagonists?
Drowsiness and sedation
What are histamine receptor agonists?
H3 agonists. E.g Betahistine Hydrochloride. Used for vertigo. Activates H-receptors on blood vessels in the inner ear.
What are muscarinic receptor antagonists?
General purpose anti-emetics. Used in motion sickness. Act on Vomiting centre and vestibular pathway.
What are the types of muscarinic receptor antagonists?
Hycosine and Scopolaimine.
What are the side effects of hycosine and scopolaimine?
Dry mouth, blurred vision
What do dopamine receptor antagonists act on?
Act on D2 receptors in the chemoreceptor trigger zone. Can treat emesis caused by uraemia, opioids, Gi disorders, viral infections.
What is Phenothiazines?
D2 receptor antagonist/ Used in severe morning sickness. Iv, oral or suppository.
What are the side effects of phenothiazines?
Sedative, hypotension, dystonia
What is metoclopramide?
D2 receptor antagonist. Increases GI motility. Oral/IM/IV.
Side effects of metoclopramide?
Movement disorders, fatigue, motor restlessness, mentruation disorders
What is Domperidone?
D2 antagonist. Has reduced central effectiveness but less side effects. Used for migraine and cytotoxic therapy induced emesis.
What do serotonin receptor antagonists act on?
5HT3 antagonists - serotonin. Act on chemoreceptor trigger zone and vagal pathway. Treat emesis caused by chemo, anaesthetics, and radiation.
What is the serotonin antagonist of choice?
Ondansetron. Side effects = headache an GI disturbances.
What are NK1R antagonists?
Act on substance P receptors. Active in late phase emesis with cytotoxic drugs.
Name a NK1R antagonist drug.
Aprepitant.
Side effects of aprepitant?
fatigue, constipation/diarrhoea, loss of appetite, hiccups. dizziness, dyspepsia, anorexia.
Which corticosteroid can treat emesis caused by chemotherapy?
Dexamethasone.
