Practical selection of antiemetics in the ambulatory setting.

Nausea and vomiting are mediated primarily by three neurotransmitter pathways: visceral stimulation releases dopamine and serotonin; vestibular and central nervous system activation release histamine and acetylcholine; and chemoreceptor trigger zone activation releases dopamine and serotonin. Clinicians can improve the effectiveness and cost-effectiveness of treatments by targeting the appropriate pathways. Antihistamines and anticholinergics are most effective in patients with vestibular-mediated nausea secondary to vertigo. Serotonin antagonists block serotonin in the intestines and chemoreceptor trigger zone, and are most effective for treating gastroenteritis. Dopamine antagonists block dopamine in the intestines and chemoreceptor trigger zone; indications for these agents are similar to those for serotonin antagonists. For treatment of mild pregnancy-induced nausea, pyridoxine with or without doxylamine is recommended, and ginger may also be effective. In patients with migraine headache-associated nausea, metoclopramide improves response to oral anti-migraine agents. Ondansetron reduces nausea and vomiting in children with acute gastroenteritis and in women with hyperemesis gravidarum.