Ondansetron Generic Name & Formulations
Ondansetron (as HCl dihydrate) 4mg, 8mg; tabs.
Selective 5-HT3 receptor antagonist.
Mechanism of Action
Ondansetron is a selective 5-HT3 receptor antagonist. Serotonin receptors of the 5-HT3 type are present both peripherally on vagal nerve terminals and centrally in the chemoreceptor trigger zone of the area postrema. It is not certain whether ondansetron’s antiemetic action is mediated centrally, peripherally, or in both sites. However, cytotoxic chemotherapy appears to be associated with release of serotonin from the enterochromaffin cells of the small intestine.
Prevention of nausea and vomiting associated with: highly emetogenic chemotherapy, including cisplatin ≥50mg/m2; initial and repeat courses of moderately emetogenic chemotherapy; and radiotherapy in patients receiving total body irradiation, single high-dose fraction to the abdomen, or daily fractions to the abdomen. Prevention of post-op nausea and vomiting.
Ondansetron Dosage and Administration
See full labeling. Highly emetogenic chemotherapy: 24mg once 30 mins before start of single-day chemotherapy (multi-day, single-dose not studied). Moderately emetogenic chemotherapy: 8mg every 8hrs for 2 doses beginning 30 mins before chemotherapy, then 8mg every 12hrs for 1–2 days after chemotherapy completed. Total body irradiation: 8mg 1–2hrs before each fraction of radiotherapy administered each day. Single high-dose fraction radiotherapy to abdomen: 8mg 1–2hrs before radiotherapy, then 8mg every 8hrs after 1st dose for 1–2 days after radiation completed. Daily fractionated radiotherapy to abdomen: 8mg 1–2hrs before radiotherapy, then 8mg every 8hrs after 1st dose for each day of radiotherapy. Post-op prophylaxis: 16mg 1hr before induction of anesthesia. For all: severe hepatic dysfunction: max 8mg/day.
Highly emetogenic chemotherapy, radiotherapy, or <4yrs of age: not recommended (see IV form). 4–11yrs: moderately emetogenic chemotherapy: 4mg every 4hrs for 3 doses beginning 30 mins before chemotherapy, then 4mg every 8hrs for 1–2 days after chemotherapy completed. Post-op prophylaxis: see IV form.
Ondansetron Boxed Warnings
<4 months of age (monitor closely). Not a substitute for nasogastric suction in gastric or intestinal peristalsis. Congenital long QT syndrome: avoid. Electrolyte abnormalities, CHF, bradyarrhythmias, concomitant drugs that prolong QT: monitor ECG. May mask progressive ileus and/or gastric distention. GI obstruction risk: monitor for decreased bowel activity. Coronary artery spasm. Monitor for myocardial ischemia during and after administration (esp. IV use; do not exceed recommended infusion rate). Phenylketonuria (ODT form). Hepatic dysfunction. Pregnancy. Nursing mothers.
See Contraindications. Profound hypotension, loss of consciousness with apomorphine. Serotonin syndrome possible esp. with concomitant serotonergic drugs (eg, SSRIs, SNRIs, MAOIs, mirtazapine, fentanyl, lithium, tramadol, IV methylene blue). May antagonize tramadol.
Ondansetron Adverse Reactions
Diarrhea, headache, fever, constipation, fatigue, transient blindness; serotonin syndrome (discontinue if occurs); rare: angina, bronchospasm, anaphylaxis, seizures, ECG changes (including QT prolongation).
Ondansetron Clinical Trials
Formerly known under the brand name Zofran.
Ondansetron Patient Counseling