Antiemetics

Question 1

Dimenhydrinate MOA

Answer 1

Competes with histamine for H1receptors on GI tract, blood vessels, and respiratory tract. Blocks chemoreceptor trigger zone, diminishes vestibular stimulation and depresses labyrinthe function through its central Ach activity

Question 2

Dimenhydrinate indications

Answer 2

Antiemetic, antihistamine, anticholinergic, antivertigo

Question 3

Dimenhydrinate contraindications and adverse effects

Answer 3

Known sensitivity to dimenhydrinate, diphenhydramine, or caffeine derivatives.

Dose related side effects such as Drowsiness and dizziness

OD same as atropine (anticholinergic) tox— blind as a bat, red as a beet, mad as the hatter, hot as a hare, dry as a bone, full as a flask

Question 4

Dimenhydrinate dosages

Answer 4

25-50mg IM, IV
12.5mg for old/frail
Administer at a rate of 25mg/min

Question 5

Dimenhydrinate pharmacokinetics

Answer 5

Onset: immediate IV, 20-30min IM
Duration: 3-6hrs

Question 6

Ondansetron MOA

Answer 6

Aka Zofran

Selectively inhibits 5-HT3 receptors, blocking serotonin both peripherally on vagal nerve terminals and centrally in the chemoreceptor trigger zone

Question 7

Ondansetron indications, contraindications and adverse effects

Answer 7

Nausea/vomit

Contra: hypersensitivity, congenital long QT

Adverse: hypotension, depression, agitation

Question 8

Ondansetron dosage

Answer 8

4.0-8.0mg PO, IV, or IM
Infusion over 15 min
IV push >30sec, preferably over 2-5min

Question 9

Ondansetron pharmacokinetics

Answer 9

Onset: 15-30min
Duration >5hrs

Question 10

Metoclopramide/maxeran MOA

Answer 10

Blocks dopamine receptors and at higher doses also blocks serotonin (5-HT4) receptors in chemoreceptor trigger zone of CNS.
Enhances Ach in upper GI, causing enhanced motility and accelerated gastric emptying and increases lower esophageal sphincter tone

Question 11

Metoclopramide/maxeran indications, contraindications and adverse effects

Answer 11

Nausea and vomiting

Contra: hypersensitivity, bowel perforation, seizure disorder, extrapyramidal (involuntary movements) reactions, MAO inhibitor therapy within 14days

Adverse: CNS depression, dysgeusia (altered taste), extrapyramidal reactions, prolong QT

Question 12

Metoclopramide/maxeran dosage

Answer 12

0.1mg/kg up to 10mg IV/IM

Question 13

Metoclopramide/maxeran pharmacokinetics

Answer 13

Onset: 1-3min iv, 10-15min IM
Peak: 15min IV
duration: 1-2 hrs