A 64-year-old woman comes to the emergency department due to intractable nausea and vomiting. She has not been able to keep anything down and feels weak and tired. The patient has had no diarrhea, constipation, or abdominal pain. She was diagnosed with breast cancer 4 weeks ago and received her first cycle of chemotherapy 1 week ago. Vital signs are within normal limits. Mucous membranes are dry. Cardiopulmonary examination is normal. Bowel sounds are normal. Which of the following agents would be most helpful in treating this patient's symptoms?

Question

A 64-year-old woman comes to the emergency department due to intractable nausea and vomiting.  She has not been able to keep anything down and feels weak and tired.  The patient has had no diarrhea, constipation, or abdominal pain.  She was diagnosed with breast cancer 4 weeks ago and received her first cycle of chemotherapy 1 week ago.  Vital signs are within normal limits.  Mucous membranes are dry.  Cardiopulmonary examination is normal.  Bowel sounds are normal.  Which of the following agents would be most helpful in treating this patient's symptoms?

Quizplus · Accepted Answer

11ec160b_3bd3_0829_9249_f79365d070e7_MD0001_00 The vomiting reflex can be activated by either humoral or neuronal stimuli. The area postrema in the fourth ventricle has a chemoreceptor trigger zone that can respond to many neurotransmitters, drugs, or toxins. The nucleus tractus solitarius (NTS) in the medulla receives information from the area postrema, gastrointestinal (GI) tract via the vagus nerve, vestibular system, and central nervous system (eg, meninges, hypothalamus). Neurons from the NTS project to other medullary nuclei and coordinate the vomiting process. The 5 major receptors involved in stimulating the vomiting reflex in the area postrema and adjacent vomiting center nuclei are M₁ muscarinic, D₂ dopaminergic, H₁ histaminic, 5-HT₃ serotonergic, and neurokinin 1 (NK1) receptors. 5-HT₃ receptor antagonists (eg, ondansetron, granisetron, dolasetron) are highly effective in preventing chemotherapy-induced vomiting. These agents act by 2 primary mechanisms: blocking vagus-mediated nausea and vomiting (from the GI tract stimuli) and blocking central serotonin receptors in the area postrema and the NTS. Other agents useful for chemotherapy-induced vomiting include NK1 receptor antagonists (eg, aprepitant), which inhibit substance P and help prevent both acute vomiting and delayed emesis; and dopamine receptor antagonists (eg, metoclopramide), which are associated with drowsiness and dystonic reactions. (Choices A and D) Histamine blockers and antimuscarinic/anticholinergic agents are most helpful for vestibular nausea and vomiting. (Choice B) Motilin regulates interdigestive migrating contractions. Erythromycin is a motilin receptor agonist used for gastroparesis. (Choice C) Mu opioid receptor agonists (eg, morphine) are useful for cancer-related pain control but often have side effects such as nausea and vomiting. Educational objective: Ondansetron inhibits serotonin (5-HT₃) receptors and is used primarily to treat nausea and vomiting following chemotherapy. 5-HT₃ receptors are located peripherally in the presynaptic nerve terminals of the vagus nerve in the gastrointestinal tract. These receptors are also present centrally in the chemoreceptor trigger zone and the solitary nucleus and tract.

A 64-Year-Old Woman Comes to the Emergency Department Due to Intractable