Which of the following has the highest affinity for 5HT3 receptors?

Ans: D (Palonosetron) Ref: The Pharmacological basis of therapeutics by Good man & Gilman - 12th edition, page no. 1345Explanation:Palonosetron is a 5HT3 antagonist similar to other antagonists such as ondansetron, dolasetron, granisetron. However palonosetron has the maximal affinity for 5HT3, receptors.These drugs are administered via intravenous route or oral routeTransdermal granisetron is also available which can be applied one day before chemotherapy and continued for seven consecutive days.All 5 HT3 antagonists are administered once daily.They are mainly used in the treatment ofChemotherapy induced nausea and vomitingNausea secondary to upper abdominal irradiationHyperemesis of pregnancyPost-operative nausea.Since palonosetron has the maximum half - life (40 hours) among the 5HTt, antagonists, it is also helpful in delayed emesis.