Nausea and Vomiting (PDQ®): Supportive care - Health Professional Information [NCI] - Prevention of Acute / Delayed Nausea and Vomiting (Emesis)
Currently, the oral and injectable ondansetron formulations are approved for use without dosage modification in patients older than 4 years, including elderly patients and patients with renal insufficiency. Oral ondansetron is given 3 times daily starting 30 minutes before chemotherapy and continuing for up to 2 days after chemotherapy is completed. Patients older than 12 years are given 4 mg per dose. Ondansetron is not approved for use in children younger than 4 years. Ondansetron clearance is diminished in patients with severe hepatic insufficiency; therefore, such patients receive a single injectable or oral dose no higher than 8 mg. There is currently no information available evaluating the safety of repeated daily ondansetron doses in patients with hepatic insufficiency. Other effective dosing schedules such as a continuous IV infusion (e.g., 1 mg/h for 24 h) or oral administration have also been evaluated.
The major adverse effects include the following: 
Ondansetron has been etiologically implicated in a few case studies involving thrombocytopenia, renal insufficiency, and thrombotic events. In addition, a few case reports have implicated ondansetron in causing EPRs. However, it is not clear in some cases whether the events described were in fact EPRs; in other reports, the evidence is confounded by concurrent use of other agents that are known to produce EPRs. Nevertheless, the greatest advantage of serotonin receptor antagonists over dopaminergic receptor antagonists is that they have fewer adverse effects. Despite prophylaxis with ondansetron, many patients receiving doxorubicin, cisplatin, or carboplatin will experience acute and delayed-phase N&V.[Level of evidence: II] A randomized, double-blind, placebo-controlled trial suggests that the addition of aprepitant, a neurokinin-1 (NK-1) receptor antagonist, may mitigate N&V.[Level of evidence: I] The optimal dose of aprepitant may be 125 mg on day 1 followed by 80 mg on days 2 to 5.[Level of evidence: I]