Ondansetron is a medication used to prevent nausea and vomiting caused by cancer chemotherapy, radiation therapy, or surgery. It is also useful in gastroenteritis. It has little effect on vomiting caused by motion sickness.

Molecular Structure


Class of Drug

Serotonin receptor antagonist, antiemetic

Mechanism of Action

Selective serotonin 5-HT3 receptor antagonist at the chemoreceptor trigger zone and peripheral vagal nerve terminals.

Indications / Dosage / Route

Routes of Administration: Oral and IV.

Condition: Antiemetic for cancer chemotherapy and postoperative nausea and vomiting

Dose: Adults, children 4-18 years: IV 0.15 mg/kg infused over 15 minutes. Start 30 minutes before chemotherapy and 4-8 hours after first dose. Alternative: 32-mg dose.

DoseAdults, children >12: PO 8 mg b.i.d. Start 30 minutes before chemotherapy, and administer next dose 8 hours later. Then 8 mg ql2h 1-2 days after chemotherapy.

©Children 4-12: PO 4 mg ti.d. Dosing regimen same as for adults.

Condition: Prevention of postoperative nausea and vomiting

Dose: Adults: PO 15 mg 1 hour before anesthesia.

Adjustment of Dosage

Kidney disease: None.

Liver disease: Severe hepatic impairment: single IV dose of 8 mg recommended.

Elderly: None

Pediatric: There is limited information for use in children <3 years.

Onset of ActionPeak EffectDuration
Rapid15-30 min4 h

Food and Drug Interactions

Food: Take without regard to meals.

Pregnancy: Category B.

Lactation: Appears in breast milk. Best to avoid.

Contraindications: Hypersensitivity to ondansetron.

Warnings / Precautions

> Use with caution in patients with liver disease.

> Use only in the first 24-48 hours following chemotherapy.

> Do not use in delayed nausea and vomiting.

> Use on a regular schedule, not on pm basis.

Clinically Important Drug Interactions

> Dmgs that increase effects/toxicity of ondansetron: cimetidine, allopurinol, disulfiram.

> Dmgs that decrease effects/toxicity of ondansetron: barbiturates, carbamazepine, rifampin, phenytoin.

Adverse Reactions

> Common: headache, diarrhea, fatigue, dizziness, constipation, musculoskeletal pain.

> Serious: hypersensitivity reactions, arrhythmias, liver toxicity, prolonged QT interval, extrapyramidal syndrome, seizures.

Parameters to Monitor

> Signs and symptoms of drug-induced extrapyramidal syndrome (pseudoparkinsonism): akinesia, tremors resting, pill rolling), shuffling gait, masklike facies, drooling. If these occur while taking this medication drug discontinuation may be required. Alternatively, administration of diphenhydramine and benztropine may be indicated.

> Monitor potassium serum level for possible hypokalemia.

Advice to Patient

> Avoid alcohol and other CNS depressant dmgs.

Further Useful Info

> Ondansetron is useful as an alternative to metoclopramide in patients likely to develop extrapyramidal reactions from metoclopramide. It has proven very useful in patients receiving highly emetogenic chemotherapy.

> When ondansetron is used for the prophylaxis or treatment of post operative nausea and vomiting, the drug is generally administered by an anesthesiologist.

> Efficacy of ondansetron for patients receiving chemotherapeutic agents with low emetogenic potential (bleomycin, busulfan, low-dose cyclophosphamide, 5-fluorouracil, vinblastine, vincristine) has not been established.

> Evaluate patient for etiology of emesis and be aware that this drug may mask signs of overdose with other drugs or underlying pathology.

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