Pharm- Anti-Emetics

Question 1

In what condition are antihistamines most effective?

Answer 1

when vomiting is caused by vestibular triggers (i.e. motion sickness)

Question 2

What is the prototypical antimuscarinic (M1 receptor antagonist)? What is it best used for?

Answer 2

Scopolamine.

Motion sickness.

Question 3

What is the MOA of 5HT3 antagonists? What are they used for? Why should you use the lowest effective dose?

(Most end is -setron)

Answer 3

MOA: act on vomiting center AND w/n the GI tract. Prevent release of 5-HT from enterochromaffin cells w/n the GI mucosa → no vagal signal.
Use: combat nausea w/ chemotherapy (Cisplatin).
B/C 5-HT receptors can become saturated.

Question 4

Why are 5HT3 antagonists used more frequently than Dopamine (D2) antagonists?

Answer 4

D2 antagonists have lots of serious SE.

Question 5

Dopamine (D2) antagonists: What 2 have BBWs?

Answer 5

1. Metochlopramide hydrochloride
BBW = chronic use → tardive dyskinesia
2. Butyrophenone (Droperidol)
May prolong QT and super sedating
BBW = causes fatal cardiac arrhythmia

Question 6

What is the MOA for Tachykinin NK 1 Receptor Antagonists? What are they sometimes combined with? If pt is on dexamethasone, what do you need to do?
(-prepitant)

Answer 6

MOA: inhibit substance P in the emetic pathway in both CNS and PNS (BLOCKS 2 PATHWAYS).
Sometimes combined w/ 5HT3 antagonists.
Decrease dose by 50% b/c it increases AUC of dexamethasone.

Question 7

Adjunct tx: What anti-emetic would you use glucocorticoids with and why?

Answer 7

5HT3 antagonists b/c increases its efficacy.