A 23-year-old woman comes to the physician due to acute nausea and vomiting. She recently returned from a vacation to Mexico and started to feel "queasy" on the last day of her trip. The patient then developed nausea with frequent vomiting and intermittent bouts of watery diarrhea. She has no visible blood in her stools. Her temperature is 36.8 C (98 F), blood pressure is 118/70 mm Hg, pulse is 86/min, and respirations are 12/min. Abdominal examination shows mild tenderness and increased bowel sounds. Improvement of this patient's vomiting would best be achieved by a medication targeting which of the following receptors?

Question

A 23-year-old woman comes to the physician due to acute nausea and vomiting.  She recently returned from a vacation to Mexico and started to feel "queasy" on the last day of her trip.  The patient then developed nausea with frequent vomiting and intermittent bouts of watery diarrhea.  She has no visible blood in her stools.  Her temperature is 36.8 C (98 F), blood pressure is 118/70 mm Hg, pulse is 86/min, and respirations are 12/min.  Abdominal examination shows mild tenderness and increased bowel sounds.  Improvement of this patient's vomiting would best be achieved by a medication targeting which of the following receptors?

Quizplus · Accepted Answer

11ec160b_3bc9_933b_9249_d3768b4d0741_MD0001_00 This patient's nausea, vomiting, and watery diarrhea are typical symptoms of classic travelers' diarrhea (TD). TD can be caused by a variety of organisms, including bacteria (eg, Escherichia coli), viruses (eg, rotaviruses), or occasionally, parasites (eg, Cryptosporidium parvum). In most cases, the illness is self-limited and treatment is symptomatic. The choice of antiemetic therapy depends on the source of the emetogenic stimulus. Conditions that cause gastrointestinal irritation (eg, infections, chemotherapy, distention) result in increased mucosal serotonin release and activation of 5-HT₃ receptors on vagal and spinal afferent nerves. These then relay their impulses to the medullary vomiting center, inducing emesis. 5-HT₃ receptor antagonists (eg, ondansetron) are well-tolerated medications that are very effective at reducing nausea and vomiting caused by gastrointestinal upset. (Choice B) Loperamide is a µ-opioid receptor agonist that functions as an antimotility agent. It is commonly used in TD to reduce diarrhea but can worsen nausea and vomiting due to colonic retention. (Choice C) Dopamine receptor antagonists (eg, metoclopramide, prochlorperazine) are effective in treating central nausea (seen in acute migraines) and also reduce migraine headache pain. Dopamine antagonists have significant adverse effects including sedation and extrapyramidal symptoms; these are not the first-line treatment for nausea due to gastrointestinal upset. (Choices D and F) First-generation H₁ receptor antagonists (eg, diphenhydramine, meclizine) and muscarinic acetylcholine receptor antagonists (eg, scopolamine) are frequently used to treat vestibular nausea (eg, motion sickness). Promethazine is a dopamine and H₁ receptor antagonist that can also treat vestibular nausea. All of these medications can cause significant sedation. (Choice E) H₂ blockers (eg, ranitidine) reduce gastric acid secretion and can alleviate symptoms of gastroesophageal reflux but do not treat nausea and vomiting. (Choice G) Somatostatin receptor agonists (eg, octreotide) inhibit bioactive amine release and are used to treat diarrhea in patients with carcinoid syndrome and vasoactive intestinal peptide-secreting tumors (ie, VIPoma). They are also used for treatment of acute esophageal variceal hemorrhage. Educational objective: 5-HT₃ receptor antagonists are useful for the treatment of visceral nausea due to gastrointestinal insults, such as gastroenteritis, chemotherapy, and general anesthesia. Antihistamines and anticholinergics are recommended for vestibular nausea. Dopamine antagonists are useful for nausea associated with migraine. __________ References: Use of antiemetic agents in acute gastroenteritis: a systematic review and meta-analysis. (http://www.ncbi.nlm.nih.gov/pubmed/18762604)

A 23-Year-Old Woman Comes to the Physician Due to Acute