WBR0727

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pharmacology
Sub Category	SubCategory::Oncology
Prompt	[[Prompt::A 52 year old male patient, with a history of tobacco use, presents to the physician's office for dyspnea and weight loss. Following appropriate work-up, he is diagnosed with limited stage small cell lung carcinoma (SCLC). The patient is then scheduled to undergo chemotherapy sessions. Before the intravenous (IV) administration of the chemotherapeutic agent, the physician prescribes a prophylactic medication to prevent the occurrence of nausea or vomiting during chemotherapy administration. What is the mechanism of action of the administered agent to manage the patient's nausea and vomiting?]]
Answer A	AnswerA::Antagonism to serotonin receptor
Answer A Explanation	AnswerAExp::Ondansetron is a serotonin (5-HT3) receptor antagonist.
Answer B	AnswerB::Antagonism to dopamine receptor
Answer B Explanation	AnswerBExp::Antiemetics like metoclopramide, may be dopamine (D2) receptor antagonists. However, metoclopramide is not as effective as ondansetron for chemotherapy-induced emesis.
Answer C	AnswerC::Agonism to serotonin receptor
Answer C Explanation	AnswerCExp::Ondansetron is an antagonist to serotonin receptor, not an agonist.
Answer D	AnswerD::Agonism to dopamine receptor
Answer D Explanation	AnswerDExp::Ondansetron is not a dopamine receptor agonist.
Answer E	AnswerE::Antagonism to serotonin and dopamine receptors
Answer E Explanation	AnswerEExp::Ondansetron is a serotonin receptor antagonist. It has no effect on dopamine receptors.
Right Answer	RightAnswer::A
Explanation	[[Explanation::Ondansetron is a 5-hydroxytryptamine (5-HT3) receptor antagonist or a serotonin receptor antagonist. It has a powerful central antiemetic activity that is very effective against nausea and vomiting associated with chemotherapy and is usually given prophylactically. However, it might also be used in other conditions, such as severe hyperemesis gravidarum. It is generally well-tolerated by patients. The most common side effects of ondansetron are: headache, constipation or diarrhea, sedation, and small increases in liver function tests that are usually self-limiting. It is almost totally eliminated by the liver with minimal amounts retrieved intact in the urine. Generally, its half life is 3.5 hours, but might vary according to age: Half-life is shorter in children and more prolonged in older patients. Educational Objective: Ondansetron, a 5HT3 or serotonin receptor antagonist, is indicated for prophylaxis against chemotherapy-associated nausea and vomiting. Reference: Kohler DR, Goldspiel BR. Ondansetron: a serotonin receptor (5-HT3) antagonist for antineoplastic chemotherapy-induced nausea and vomiting. DICP. 1991; 25(4):367-80. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::ondansetron, WBRKeyword::chemotherapy, WBRKeyword::nausea, WBRKeyword::vomiting, WBRKeyword::side, WBRKeyword::effect, WBRKeyword::serotonin, WBRKeyword::receptor, WBRKeyword::antagonist, WBRKeyword::antagonism, WBRKeyword::mechanism, WBRKeyword::action, WBRKeyword::dopamine, WBRKeyword::metoclopramide, WBRKeyword::antiemetic, WBRKeyword::antiemesis
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::