Antiemetics pharm

Question 1

pathophysiology of nausea and vomiting?

Answer 1

caused by noxious stimulation of 1 or more of 4 sites which can trigger vomiting centre.

1) chemoreceptor trigger zone in the area postrema of the floor of 4th ventricle.

2) GI tract

3) Vestibular system

4) higher centres in CNS.

Question 2

examples of Serotonin 5-HT3 antagonists and their half life

Answer 2

ondansetron ( 4-9 hours)
palonosetron ( 40-50 hours)
Granisetron (9-12 in cancer patients)

Question 3

moa of Ondansetron

Answer 3

1) act on 5-HT3 receptors in GI tract.
2) 5-HT3 receptors in CNS dont play a part
3) efficacy is enhanced when used with corticosteroids and NK1 receptor antagonist.
4) to give IV 30 mins or orally 1 hour before chemotherapy to prevent acute vomiting.
5) not effective for delayed vomiting more than 24 hours.

Question 4

adverse effects of ondansetron

Answer 4

Eliminated by hepatic metabolism and renal and hepatic excretion
- But generally dose reduction not required in elderly or patients with renal insufficiency
- Dose reduction of ondansteron may be required for patients with hepatic insufficiency
- Generally well-tolerated but may cause headache, dizziness and constipation
- Small risk of cardiac arrhythmia (prolongation of the QT interval)
- Undergo P450 metabolism
- Do not appear to interfere with metabolism of other drugs
- But other drugs may reduce hepatic clearance of the 5-HT3 antagonists

Question 5

can i take ondansetron during early pregnancy?

Answer 5

No, it may cause orofacial malformations.

Question 6

examples of corticosteroids

Answer 6

dexamethasone and methylprednisolone