Anti Emetics Flashcards
What is emesis
Forceful evacuation of gastric contents
Protective physiological mechanism when something harmful is ingested
What region is referred to as the brain stem emetic control centre or the dorsal vagal complex
Brain stem in a neural network on the dorsal surface of the medulla oblongata
What are the three major inputs to the dorsal vagal complex causing vomiting?
Chemoreceptor
Vagal pathway
Vestibular pathway
Chemoreceptor trigger zone in emesis
Endogenous substances, toxins, drugs
Vagal pathway in emesis
Sensory input (pain, smell, sight, thought)
Stimuli from pharynx
Stimuli from gi tract
Vestibular pathway in emesis
Disorientating motion
The therapeutic approach to emesis involves…
Blocking the neurotransmitters involved in triggering the response
Describe the receptor pharmacology of emesis
Vomiting centre - muscarinic, histamine, neurokinin, serotonin
Vestibular pathway- histamine, muscarinic
Vagal - serotonin
Chemoreceptor- dopamine, neurokinin, serotonin
Chemoreceptor trigger zone receptors
Dopamine (d2)
Substance p/ neurokinin (NK)
Serotonin (5HT3)
Vagal pathway receptors (emesis)
Serotonin (5HT3)
Vestibular pathway receptors (emesis)
Histamine (H2)
Muscarinic (M)
Cyclizine
Anti emetic histamine receptor antagonist
Motion sickness
SE:drowsiness or sedation
Cinnarizine
Anti emetic histamine receptor antagonist
Motion wickedness, vestibular disorders eg Ménière’s disease, vertigo
SE: drowsiness, sedation
Promethazine
Anti emetic histamine receptor antagonist
Severe morning sickness in pregnancy
SE: drowsiness, sedation
Betahistine hydrochloride (sero)
Activates H receptors on blood vessels in the inner ear
Local vasodilation
Increased permeability
Reverses problem of endolymphatic hydrops
SE: gi, headache, rash, pruritus