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# Ondem (ondansetron)
## Overview
Ondem is a brand name for ondansetron, a selective 5-HT3 receptor antagonist. It is an antiemetic used to prevent nausea and vomiting.
## Primary Indications
- Prevention of chemotherapy-induced nausea and vomiting (CINV)
- Prevention of radiotherapy-induced nausea and vomiting (RINV)
- Prevention of postoperative nausea and vomiting (PONV)
- Treatment of established postoperative nausea and vomiting
## Adult Dosing
- **CINV (moderately to highly emetogenic)**: 8 mg IV or 16 mg PO (as a single dose) 30 minutes before chemotherapy; or 8 mg PO/IV every 8–12 hours for 1–2 days post-chemotherapy. Maximum single dose: 16 mg IV (due to QTc risk).
- **RINV**: 8 mg PO three times daily.
- **PONV prevention**: 4 mg IV at induction of anesthesia.
- **PONV treatment**: 4 mg IV or IM as a single dose.
## Pediatric Dosing
- **CINV (≥6 months)**: 0.15 mg/kg/dose IV (max 8 mg) 30 minutes before chemotherapy, then every 4–8 hours; or 4–8 mg PO every 8–12 hours based on BSA.
- **PONV prevention (≥1 month)**: 0.1 mg/kg IV (max 4 mg) as a single dose.
- **PONV treatment (≥1 month)**: 0.1 mg/kg IV (max 4 mg).
- **Maximum single IV dose**: 8 mg in children; 16 mg in adolescents (weight-based protocols may vary).
## Dose Adjustments
- **Hepatic impairment (severe, Child-Pugh C)**: Maximum total daily dose 8 mg (IV or PO).
- **Renal impairment**: No adjustment needed for mild-moderate; limited data for severe—use with caution.
- **QTc prolongation risk**: Avoid doses >16 mg IV single dose; consider ECG monitoring in at-risk patients.
## Contraindications
- Hypersensitivity to ondansetron or any component
- Concomitant use with apomorphine (risk of profound hypotension and loss of consciousness)
- Congenital long QT syndrome (relative contraindication; use with caution)
## Adverse Effects
- **Common**: Headache, constipation, diarrhea, fatigue, dizziness
- **Serious**: QT interval prolongation (dose-dependent), serotonin syndrome (rare, especially with other serotonergic drugs), hypersensitivity reactions (including anaphylaxis)
## Key Drug Interactions
- **Apomorphine**: Contraindicated (additive hypotension, CNS depression)
- **QT-prolonging agents** (e.g., class III antiarrhythmics, certain antipsychotics, macrolides): Increased risk of torsades de pointes
- **Serotonergic drugs** (e.g., SSRIs, SNRIs, MAOIs): Increased risk of serotonin syndrome
- **CYP3A4 inducers/inhibitors**: Minimal clinical impact; ondansetron is metabolized by multiple CYP enzymes
## Monitoring
- ECG in patients with electrolyte abnormalities, CHF, bradyarrhythmias, or concurrent QT-prolonging drugs
- Signs of serotonin syndrome (agitation, hyperthermia, clonus, hyperreflexia) when used with other serotonergic agents
- Hepatic function in severe liver disease
## Clinical Pearls
- Ondansetron is less effective for motion sickness or gastroparesis.
- IV push should be administered over 2–5 minutes to reduce risk of QT prolongation.
- Oral dissolving tablets (ODT) are available for patients with nausea/vomiting who cannot swallow pills.
- For highly emetogenic chemotherapy, combine with dexamethasone and aprepitant for optimal control.
- **Uncertainty**: Pediatric dosing for CINV may vary by protocol; consult local guidelines for age/weight-specific regimens.
*This information is for educational purposes only. Always verify current prescribing information from the manufacturer's label and local clinical guidelines before administering.*
