5-HT3 Receptor Antagonists
Four serotonin receptor antagonists—ondansetron, granisetron, dolasetron, and palonosetron—are available in the United States. Tropisetron, while not approved by the FDA, is available internationally. Agents in this class are thought to prevent N&V by preventing serotonin, which is released from enterochromaffin cells in the gastrointestinal (GI) mucosa, from initiating afferent transmission to the CNS via vagal and spinal sympathetic nerves. The 5-HT3 receptor antagonists may also block serotonin stimulation at the CTZ and other CNS structures.
Several studies have demonstrated that ondansetron produces an antiemetic response that equals or is superior to high doses of metoclopramide, but ondansetron has a superior toxicity profile compared with dopaminergic antagonist agents.[18,19,20,21,22][Level of evidence: I][23,24] Ondansetron (0.15 mg/kg) is given IV 15 to 30 minutes prior to chemotherapy and is repeated every 4 hours for two additional doses. Alternatively, for patients older than 18 years, a large multicenter study determined that a single 32-mg dose of ondansetron is more effective in treating cisplatin-induced N&V than a single 8-mg dose and is as effective as the standard regimen of three doses at 0.15 mg/kg given every 4 hours starting 30 minutes before chemotherapy.[Level of evidence: I] A single-center retrospective chart review has reported ondansetron-loading doses of 16 mg/m2 (maximum, 24 mg) IV to be safe in infants, children, and adolescents.
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 should receive 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 should 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 headache (which can be treated with mild analgesics), constipation or diarrhea, fatigue, dry mouth, and transient asymptomatic elevations in liver function tests (alanine and aspartate transaminases), which may be related to concurrent cisplatin administration. 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]