Classify anti-emetic agents by describing their mechanism of action and provide examples.
Successful candidates were those who discussed the multiple locations in the vomiting
pathway where a drug acts, the receptors involved and discussed 5 or more classes.
Several approaches can be taken to this topic. Classification by drug group works well and
then allows more detail to be provided about possible receptor activity.
Anithistamines: Promethazine H1 ++++ M ++ D2 ++ 5-HT3
Anitcholinergics: Scopalamine H1 + M ++++ D2 + 5-HT3
Benzamines: Metoclopromide H1 + M -- D2 +++ 5-HT3 ++,
Neuroleptics: Droperidol H1 + M - D2 +++ 5-HT3 +,
5-HT3 Antagonists: Ondansetron H1 - M - D2 - 5-HT3 ++++, Granisetron H1 ++++ M ++
D2 ++ 5-HT3 ; Glucocorticoids: Dexamethasone H1 - M - D2 - 5-HT3 -,
Cannabinoids: direct on vomiting center.
An alternative approach involves a discussion of the distribution of receptor sites: nucleus
vestibularis H1 M, area postrema (chemoreceptor trigger zone) 5-HT3 D2 M1 H1, nucleus
tractus solitarius 5-HT3 D2 M H2 and then discuss which drugs act where. This material has
also been previously covered in the viva examination and knowledge of both drug properties
and receptor distribution is often required.
Few answers detailed relative activity at various receptors types – “+” scale illustrated above
would be sufficient to convey an understanding to the examiners.