Antiemetics Flashcards
Where is the vomiting center?
Nucleus of the Tractus Solitarius
Reticular Formation of the Medulla Oblongata
Where is the CRTZ?
Chemoreceptor Trigger Zone is on the floor of the fourth ventricle, which is OUTSIDE THE BLOOD BRAIN BARRIER
This means a substance doesn’t have to cross the BBB to activate the CRTZ
Who is at highest risk of PONV?
Women
Nonsmokers
Hx of Motion Sickness
Hx of PONV
Why are women more likely to have PONV?
It has to be related to the effects of progesterone or estrogen, because the extent of PONV varies with the menstrual cycle and decreases after menopause
How does the incidence of PONV change with age in adults?
Decreases per decade in adults
How does the incidence of PONV change with age in children?
increases with age
very low incidence in children < 3
What anesthesia-related drugs have been linked to PONV?
inhalation anesthetics
Nitrous Oxide
Neostigmine
Opioids
What is serotonin’s role in N/V?
Serotonin is released from the enterochromaffin cells of the SI when there is a caustic or irritating substance
What kind of N/V are 5-HT3 receptor antagonists NOT useful against?
N/V caused by vestibular stimulation
What drugs are 5-HT3 antagonists?
all of the “-setron” drugs
What are the most common side effects from Ondansetron treatment??
Headache and diarrhea
Does acetylcholine trigger or inhibit the CRTZ?
Triggers it. Anticholinergics reduce N/V
Which cholinergic receptors activate the CRTZ?
Muscarinic receptors in the VESTIBULAR SYSTEM
This is why scopolamine is helpful for motion sickness but ondansetron isnt
Why are scopolamine patches so much more desirable than IV or PO doses?
IV or PO administration requires much larger doses, which leads to more side effects (sedation, cycloplegia, dry mouth)
Why is scopolamine helpful in patients on a morphine PCA or morphine PCEA?
morphine stimulates the vestibular apparatus
Why do morphine and synthetic opioids cause N/V?
They increase vestibular sensitivity to motion
If a patient with a scopolamine patch has one blown pupil, what should you suspect?
They’ve probably touched the patch and then touched their eye
Contamination of the eye will cause anisocoria, and it will go away with time
What is Central Anticholinergic Syndrome?
Blockade of muscarinic cholinergic receptors and competitive inhibition of the effects of Ach in the CNS cause restlessness and hallucinations all the way to somnolence and unconsciousness
Which anticholinergics cause Central Anticholinergic Syndrome?
Scopolamine and Atropine
Glycopyrrolate doesn’t cross the BBB
Which drug is used to treat Central Anticholinergic Syndrome?
Physostigmine
This is the only anticholinesterase that crosses the BBB
What does anticholinergic overdose look like?
Dry and flushed skin
Dry mouth
Difficulty swallowing and talking
blurry vision
Photophobia
Who is susceptible to atropine fever?
Little kids
What is barrier pressure and how is it effected by anticholinergics?
The difference between gastric pressure and LES pressure
Decreased by anticholinergics, increasing the risk of aspiration
Antagonism of which receptors results in decreased N/V?
5-HT3
Histamine
Dopamine
Neurokinin-1
Muscarinic
Which histamine receptor is responsible for N/V?
H1
Which antihistamines are effective in treating N/V?
Nonspecific H1 receptor blockers:
Diphenhydramine, Promethazine, Dramamine
What are the most common side effects from antihistamines?
Anticholinergic effects: dry mouth and somnolence
Why is Dimenhydrinate (Dramamine) so helpful in treatment motion sickness?
inhibition of the vestibular nuclei 2/2 decreased RAS input
Which dopamine receptor subtype is found in the CRTZ?
D2
How does Metoclopramide reduce N/V?
- Antidopaminergic
- Stimulates the GI tract via cholinergic mechanisms
Which patients should not receive Metoclopramide?
Patients with Parkinson, RLS, or other movement disorder related to dopamine depletion
Why do droperidol and Haldol reduce N/V?
They antagonize the D2 receptor
What receptors do Haldol and Droperidol block?
- Dopamine
- Norepinephrine
- Ach
- Histamine
Name two Neurokinin-1 antagonists
Aprepitant and Fosaprepitant
How does aprepitant reduce N/V?
Antagonizes Neurokinin-1 receptor, whose ligand is Substance P
Why does versed decreased N/V?
may decrease synthesis and release of dopamine in the CRTZ
What cases of N/V are cannabinoids useful in treating?
CINV, but not PONV
How does stomach pH influence gastric motility?
Neutralizing gastric pH increases gastric motility by increasing gastrin release
It also increases LES tone, but not via gastrin
What electrolyte derangements can be caused by calcium containing antacids?
Hypercalcemia
Hypophosphatemia
What are the side effects of aluminum-containing antacids?
Hypomagnesemia
Hypophosphatemia
Anemia
Constipation
Why is bicitra the preferred oral antacid?
It is less likely to cause a foreign body reaction if aspirated
AND
more complete and rapid action
Acid rebound is a side effect unique to which antacids?
Calcium containing antacids
What is milk-alkali syndrome?
Hypercalcemia
Increased BUN and Cr
Systemic Alkalosis
Most commonly associated with ingestion of large amounts of CaCO3 and > 1 L milk every day
