BRAND NAMES
 MECHANISM OF ACTION
Ondansetron is an antinauseant and antiemetic agent. It acts as a selective serotonin 5-HT3 receptor antagonist.
Cancer chemotherapy may be associated with a high incidence of nausea and vomiting, particularly when certain agents, such as cisplatin, are used. 5-HT3 receptors are located on the nerve terminals of the vagus in the periphery and centrally in the chemoreceptor trigger zone of the area postrema. It is thought that chemotherapeutic agents produce nausea and vomiting by releasing serotonin from the enterochromaffin cells of the small intestine and that the released serotonin then activates 5-HT3 receptors located on vagal afferents to initiate the vomiting reflex.
Postoperative nausea and vomiting is influenced by multiple patient,surgical and anesthesia related factors and is triggered by release of serotonin in a cascade of neuronal events involving both the central nervous system and the gastrointestinal tract. The 5-HT3 receptor has been demonstrated to selectively participate in the emetic response.
- Injection and tablets:
- Prevention of nausea and vomiting associated with initial and repeat courses of emetogenic cancer chemotherapy.
- Prevention of postoperative nausea and/or vomiting.
- Off label: Nausea and vomiting of pregnancy (Hyperemesis Gravidarum): Despite the fact that it is not indicated, women are being prescribed this drug for the treatment of nausea and vomiting of pregnancy (NVP). Ondansetron does not appear (although the sample size is limited) to be associated with an increased risk for major malformations above baseline. 
Prevention of Nausea and Vomiting Associated With Highly Emetogenic Cancer Chemotherapy: The recommended adult oral dosage is 24 mg given as three 8-mg administered 30 minutes before the start of single-day highly emetogenic chemotherapy, including cisplatin ≥ 50 mg/m2. Multiday, single-dose administration of a 24 mg dosage has not been studied.
Prevention of Nausea and Vomiting Associated With Moderately Emetogenic Cancer Chemotherapy:
- The recommended adult oral dosage is one 8-mg given twice a day. The first dose should be administered 30 minutes before the start of emetogenic chemotherapy, with a subsequent dose 8 hours after the first dose.
- Pediatric Use: For pediatric patients 12 years of age and older, the dosage is the same as for adults. For pediatric patients 4 through 11 years of age, the dosage is one 4-mg given 3 times a day. The first dose should be administered 30 minutes before the start of emetogenic chemotherapy, with subsequent doses 4 and 8 hours after the first dose. 4-mg should be administered 3 times a day (every 8 hours) for 1 to 2 days after completion of chemotherapy.
Prevention of Nausea and Vomiting Associated With Radiotherapy, Either Total Body Irradiation, or Single High-Dose Fraction or Daily Fractions to the Abdomen:
- The recommended oral dosage is one 8-mg given 3 times a day.
- For total body irradiation, one 8-mg should be administered 1 to 2 hours before each fraction of radiotherapy administered each day.
- For single high-dose fraction radiotherapy to the abdomen, one 8-mg should be administered 1 to 2 hours before radiotherapy, with subsequent doses every 8 hours after the first dose for 1 to 2 days after completion of radiotherapy.
- For daily fractionated radiotherapy to the abdomen, one 8-mg should be administered 1 to 2 hours before radiotherapy, with subsequent doses every 8 hours after the first dose for each day radiotherapy is given.
Hyperemesis Gravidarum: 10 mg IV every 8 hours when necessary.
 DOSAGE FORMS AND STRENGTHS
- 4 mg tablets
- 4 mg disintegrating tablets
- 8 mg tablets
- 8 mg disintegrating tablets
- Injection (2 mg/mL): 20 mL multidose vials
- Hypersensitivity to Ondansetron
- Concomitant use of apomorphine (beacause of a risk of profound hypotension and loss of consciousness)
 WARNINGS AND PRECAUTIONS
- Hypersensitivity reactions including anaphylaxis and bronchospasm, have been reported in patients who have exhibited hypersensitivity to other selective 5-HT3 receptor antagonists.
- QT prolongation occurs in a dose-dependent manner. Cases of Torsade de Pointes have been reported. Avoid Ondansetron in patients with congenital long QT syndrome.
- Apomorphine: Concomitant use of Apomorphine can induce a profound hypotension and loss of consciousness.
 PREGNANCY AND LACTATION
- Pregnancy Category B (US), Ondansetron should be used during pregnancy only if clearly needed.
- Caution should be exercised when ondansetron is administered to a nursing woman
 SIDE EFFECTS
- Most common adverse reactions are diarrhea, headache, and fever.
 RELATED LINKS
|5-HT3 receptor antagonists||Dolasetron • Granisetron • Ondansetron • Palonosetron • Tropisetron|
|Dopamine antagonists||Alizapride • Bromopride • Clebopride • Domperidone • Metoclopramide • Prochlorperazine • Thiethylperazine|
|H1 antagonists||Dimenhydrinate • Meclizine|
|NK1 receptor antagonists||Aprepitant • Fosaprepitant • Maropitant|
|Motion sickness||Cinnarizine • Dimenhydrinate • Meclizine • Meclizine/Pyridoxine • Scopolamine (Patch)|
|Pregnancy||Meclizine/Pyridoxine • Ondansetron|