GI Medications Flashcards
What are patient factors that relate to PONV?
women
non-smokers
hx motion sickness
hx PONV
What are surgical factors that relate to PONV?
length of surgery
laparotomies & laparoscopies
gynecologic
ENT
breast
orthopedic
What are anesthesia factors that relate to PONV?
inhalation agents
nitrous oxide
neostigmine
narcotics
etomidate
Where is the vomiting center located?
medulla oblongata
How does the vomiting center work?
efferent pathways > vagal sympathetic and parasympathetic chains > motor response
Where are signals transmitted from?
chemoreceptor trigger zone
vestibular apparatus
thalamus and cerebral cortex
neurons in GI tract
What are the neurotransmitters and corresponding receptors that are involved with PONV?
dopamine: dopamine receptors
serotonin: 5HT3 receptors
acetylcholine: muscarinic receptors
histamine: histamine receptors
substance P: neurokinin receptors
What anticholinergics are used to treat PONV?
scopolamine
atropine
hyosine
What benzamides are used to treat PONV?
metoclopramide
What benzodiazepines are used to treat PONV?
midazolam
What butrophenones are used to treat PONV?
droperidol
haloperidol
What cannabinoids are used to treat PONV?
dronabinol
nabilone
What glucocorticoids are used to treat PONV?
dexamethasone
What 5HT3 antagonists are used to treat PONV?
ondansetron
dolasetron
granisetron
palonosetron
ramosetron
tropisetron
What neurokinin-1 antagonsists are used to treat PONV?
aprepitant
fosprepitant
What phenothiazines are used to treat PONV?
promethazine, prochoperazine, chlorpromazine
What is the mechanism of action of Scopolamine?
thought to block transmission from vestibular apparatus to medulla
What is the dose of Scopolamine?
5 mcg/hr for 72 hours
*best if given 4 hours before stimulus
What is Scopolamine used to treat?
motion sickness
PONV from middle ear surgery
N/V from PCA or epidural morphine
What are the side effects of Scopolamine?
visual disturbances
*dilated pupils
What is the mechanism of action of Metoclopramide?
stimulate the GI tract via CHOLINERGIC mechanism and ANIT-DOPAMINERGIC effect
What patients do we use caution with Metoclopramide?
RLS
Parkinson’s
*due to anti-dopamine effects
What is the mechanism of action of Midazolam?
thought to decrease the stimulation and release of dopamine in the CRTZ
When should Midazolam be given if using to treat PONV?
at the end of the case
What is the mechanism of action of Droperidol?
competitive dopamine antagonist
What are the receptor and ligands for Droperidol?
receptor: D1
ligands: dopamine & GABA
What is the dose of Droperidol?
0.625 mg (initial)
1.25 mg (rescue)
What patients do we use caution with Droperidol?
RLS
Parkinson’s
*due to anti-dopamine effects
What is a critical side effect of Droperidol?
QT prolongation
*seen in high doses
What is the mechanism of action of Dexamethasone?
inhibits prostaglandin release and controls endorphin release
What is the dose of Dexamethasone?
4 mg
What patients do we use caution with Dexamethasone?
diabetic patients and obese
*due to potential hyperglycemia
What kind of receptor is a 5HT3?
ligand-gated ion channel (Na & K)
inotropic
excitatory
What other body functions does serotonin affect?
mood, cognition, sleep
What other effects does serotonin have?
addiction
aggression
vasoconstriction
increased intestinal motility
learning and memory consolidation
What are 5HT3 antagonists used to treat?
PONV
N/V due to chemotherapy
*does not work for motion sickness, no 5HT3 receptors in the vestibular apparatus
What is the dose of Ondansetron?
4 mg
What is the onset of Ondansetron?
30-60 minutes
What are the side effects of Ondansetron?
headache
QT prolongation
diarrhea
Why does Ondansetron have very few CNS effects?
does not cross BBB
What is Tropisetron used to treat?
symptoms of carcinoid syndrome
What is the dose and duration of Granisetron?
dose: 0.1 mg
duration: 24 hours
What is special about Dolasetron?
has an active metabolite
What is Substance P?
primary neurotransmitter produced by pain/temperature afferent peripheral neurons
What is the mechanism of action of Aprepitant?
competitive antagonist at NK1 receptors
What is Aprepitant used to treat?
N/V due to chemotherapy
What is a critical side effect of Aprepitant?
can inhibit steroidal birth control for 7-10 days
What is the mechanism of action of Promethazine?
antagonizes H1 (histamine) and M1 (acetylcholine) receptors
Where are H1 receptors located?
vascular smooth muscle
bronchial smooth muscle
CNS
What are some H1 receptor antagonists?
Diphenhydramine (Benadryl)
Dimenhydrinate (Dramamine)
Loratadine (Claritin)
Hydroxyzine (Atarax)
Promethazine (Phenergan)
Where are H2 receptors located?
stomach
What are some H2 receptor antagonists?
famotidine
Where are H3 receptors located?
presynaptic nerve terminals
*reduces further histamine release
What is the mechanism of action of H1 antagonists?
competitively blocks H1 receptors
What is the dose of Diphenhydramine?
25-50 mg
What is the onset and duration of Diphenhydramine?
onset: 3 minutes
duration: 1-7 hours
What receptors does Dymenhydrinate block?
H1 & M1 (vestibular apparatus)
*effective against motion sickness and as a sleep aid
What is a critical side effect of Promethazine?
orthostatic hypotension
*adrenoceptor blocking action
potentiates anesthetic sedative effects
What are H1 receptor antagonists used to treat?
allergic reactions
motion sickness
N/V of pregnancy (Promethazine)
What patients are at increased risk of aspiration?
pregnant women
diabetics
mask induction (no protected airway)
emergency cases
What is the mechanism of action of antacids?
removes H+ ions
neutralize gastric pH
What is the duration of action of antacids?
about 30 minutes
What are side effects of antacids?
increase gastric volume
change the metabolism of other drugs
What antacid is used prior to cesarean sections? What is the dose and when is it given?
Bicrita
15-30 mL
immediately before induction
What are some H2 receptor antagonists?
Cimetidine (Tagamet)
Ranitidine (Zantac)
Famotidine (Pepcid)
Nizatidine (Axid)
What is the mechanism of action of H2 antagonists?
selectively and reversibly block histamine at H2 receptors
What are H2 antagonists used to treat?
peptic duodenal ulcer
gastric ulcer
erosive esophagitis
hypersecretory conditions
What are critical side effects of Cimetidine?
*CNS dysfunction in elderly (slurred speech, delirium, confusional states)
*liver toxicity
Do H2 antagonists cross the placenta and enter breastmilk?
Yes!
*can affect the baby
What drugs when given with Cimetidine can lead to toxicity due to a decrease in hepatic blood flow and inhibition of the P450 system?
What drugs when given with Cimetidine can lead to toxicity due to a decrease in hepatic blood flow and inhibition of the P450 system?
Warfarin
Dilantin
Propranolol
Metoprolol
Labetalol
Quinidine
Caffeine
Lidocaine
Theophylline
Alprazolam
Diazepam
Flurazepam
Triazolam
Carbamazepine
Ethanol
Tricyclic antidepressants
Calcium channel blockers
What are some proton pump inhibitors?
Omeprazole
Pantoprazole
Esomerprazole
Lansoprazole
What is the effect of proton pump inhibitors?
increase gastric fluid pH
decrease gastric fluid volume
What type of drug is Omeprazole?
prodrug
*becomes PPI after metabolism
What is the onset of Omeprazole and when is it best taken in regards to surgery?
couple of days
night before surgery
Does Omeprazole cross the BBB?
Yes!
Can cause headaches, agitation, confusion
What is Omeprazole specifically used to treat?
Zollinger-Ellison syndrome
What is the mechanism of action of Metoclopramide?
cholinergic stimulation & dopamine antagonism
increasing lower esophageal sphincter tone, enhancing peristaltic contractions, accelerating the rate of gastric emptying
Does Metoclopramide cross the BBB?
Yes!
also affects CRTZ
What is the dose of Metoclopramide?
10-30 mg
What patients do we use caution with Metoclopramide?
RLS
Parkinson’s
patients on MAOI or tricyclic antidepressants
GI surgery
patients taking phenothiazines or butrophenones (r/t dopamine)
Does Metoclopramide change gastric pH?
No!
What is Metoclopramide used to treat?
diabetic gastroparesis
antiemetic
GERD
enteral feeding assist in chronically ill
What are the side effects of Metoclopramide?
placental transfer
abdominal cramping
extrapyramidal effects (anti-cholinergic)
prolonged succinylcholine effect (inhibits plasmaesterase synthesis)
What are anticholinergic side effects?
red as a beet (flushed skin)
dry as a bone (dry eyes, mouth, & skin)
blind as a bat (dilated pupils, blurry vision)
mad as a hatter (confusion, agitation)
hot as a hare (overheating)
full as a flask (urinary retention)