Question 23

Classify antiemetic drugs and give an example from each group (60% of marks). 
Outline the gastrointestinal effects of metoclopramide (40% of marks).

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College Answer

Antiemetics, as a topic has been frequently asked, in various formats in the past. Candidates 
who performed well had a good depth and breadth of knowledge as well as sufficient 
integration of knowledge to be able to classify and understand the basis to the various 
classifications. Essentially it was expected that candidates mention the classifications of 
Anticholinergics, Antihistamines, Anti 5HT, Antidopaminergics (benzamides, 
butyrophenones, phenothiazines), Steroids and other agents with known antiemetic activity 
(e.g. propofol, benzodiazepines, etc). In relation to metoclopramide it was expected that 
candidates would mention that it lowers pressure threshold for occurrence of intestinal 
peristaltic reflex, reduces intestinal muscle fatigue, enhances frequency and amplitude of 
longitudinal muscle contraction, coordinates gastric, pyloric and duodenal activity to 
improve GI motility, mechanism of action appears to depend on intramural cholinergic 
neuron, acts primarily by augmenting release of ACh and perhaps by inhibition of 5-HT 
release, increases lower oesophageal sphincter pressure, relaxes the pyloric sphincter and 
antagonize the inhibitory neurotransmitter, dopamine.