A nurse is preparing to administer medication to a client about to begin chemotherapy and has a history of severe nausea and vomiting as a result. Which medication should the nurse anticipate administering prophylactically to best prevent nausea and vomiting related to chemotherapy?

A. Polyethylene glycol, an osmotic laxative: Polyethylene glycol is used to treat constipation by drawing water into the intestines. It does not prevent chemotherapy-induced nausea or vomiting and is not effective for this purpose. B. Omeprazole, a proton pump inhibitor: Omeprazole decreases gastric acid production and is used for gastroesophageal reflux or ulcers. It does not prevent chemotherapy-induced nausea or vomiting and is not indicated for prophylaxis. C. Loperamide, an opioid: Loperamide is an antidiarrheal that slows intestinal motility. It does not prevent nausea or vomiting related to chemotherapy and is not used for this purpose. D. Ondansetron, a selective 5-HT3 receptor antagonist given 30 minutes before chemotherapy: Ondansetron blocks serotonin receptors in the chemoreceptor trigger zone and gastrointestinal tract, preventing nausea and vomiting. Administering it 30 minutes before chemotherapy provides effective prophylaxis, in patients with severe chemotherapy-induced nausea and vomiting.