ondansetron
Brand: Zofran
Prototype Drug
Drug Class: antiemetic
Drug Family: antiemetic
Subclass: 5-HT3 serotonin receptor antagonist
Organ Systems: gastrointestinalcns
Mechanism of Action
Selective 5-HT3 antagonist blocking serotonin receptors in GI vagal afferents and centrally in area postrema; most effective for chemotherapy-induced nausea (high serotonin release).
5-HT3 serotonin receptor (peripheral vagal afferents and central CTZ)
Indications
- chemotherapy-induced nausea/vomiting (CINV)
- post-operative nausea/vomiting (PONV)
- pregnancy nausea/vomiting (off-label but common)
- radiation-induced nausea
Contraindications
- congenital QT prolongation
- electrolyte abnormalities (hypokalemia, hypomagnesemia)
Adverse Effects
Common
- headache
- constipation
- dizziness
- QT prolongation
Serious
- QT prolongation/TdP (dose-dependent)
- serotonin syndrome (with other serotonergic agents)
Pharmacokinetics (ADME)
| Absorption | ~60% oral bioavailability |
| Distribution | moderate |
| Metabolism | extensive hepatic CYP3A4 and CYP1A2 |
| Excretion | renal 5% unchanged |
| Half-life | 3.5-5.9 hours |
| Onset | 0.5-1 hours |
| Peak | 1-2 hours |
| Duration | 6-8 hours |
| Protein Binding | 70-76% |
| Vd | 1.9 L/kg |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| serotonergic drugs (SSRIs, MAOIs) | serotonin syndrome risk | major |
| QT-prolonging drugs | additive QT prolongation | major |
| apomorphine | profound hypotension if given together — absolute contraindication | major |
Nursing Considerations
- QT prolongation: ECG before high-dose IV use; avoid with known QT prolongation
- Constipation is common side effect — manage with stool softeners
- IV single dose 32 mg is removed from US market due to QT risk; use 0.15 mg/kg per dose or 8 mg doses
- Serotonin syndrome risk with concomitant serotonergic agents
Clinical Pearls
- 5-HT3 antagonism most effective for CINV because chemo releases serotonin from enterochromaffin cells
- QT dose-dependency: 32 mg single IV dose removed from market; current max 16 mg IV dose
- Pregnancy nausea: widely used off-label; no teratogenicity signal but avoid first-trimester if possible
Safety Profile
Pregnancy use-with-caution
Lactation use-with-caution
Renal Adjustment Not required
Hepatic Adjustment Required
TDM Not required
Concordance Terms
Cross-referenced clinical concepts — click any term to see all content where it appears.