ONDANSETRON HYDROCHLORIDE
Clinical safety rating: safe
Drugs that prolong the QT interval may have additive effects Can cause QT prolongation and subsequent arrhythmias.
Selective serotonin 5-HT3 receptor antagonist; blocks serotonin binding at 5-HT3 receptors in the chemoreceptor trigger zone (CTZ) and gastrointestinal tract, inhibiting emetic reflex.
| Metabolism | Hepatic via CYP450 enzymes, primarily CYP1A2, CYP2D6, and CYP3A4. |
| Excretion | Renal: 5% unchanged; hepatic metabolism accounts for >95% of elimination; metabolites excreted in urine (44-60%) and feces (25-33%). |
| Half-life | Terminal elimination half-life is approximately 3-6 hours in adults, 4-6 hours in elderly, and 5-7 hours in severe hepatic impairment (Child-Pugh Class C). |
| Protein binding | 70-76% bound to plasma proteins (primarily to α1-acid glycoprotein). |
| Volume of Distribution | Apparent volume of distribution is approximately 1.8-2.4 L/kg, indicating extensive extravascular distribution. |
| Bioavailability | Oral: 56-71% (due to first-pass metabolism); IM: 100%; IV: 100%. |
| Onset of Action | Oral: 30-60 minutes; IV: 1-5 minutes; IM: 10-15 minutes; Orally disintegrating tablet: 30-60 minutes. |
| Duration of Action | Duration of antiemetic effect is approximately 8-12 hours for oral/IV administration; may be shorter in children. |
8 mg orally or intravenously every 8 hours; maximum 24 mg/day. For prevention of chemotherapy-induced nausea and vomiting, 8 mg intravenously or 24 mg orally 30 minutes before chemotherapy.
| Dosage form | INJECTABLE |
| Renal impairment | No dose adjustment required for mild-moderate renal impairment. For severe renal impairment (CrCl <30 mL/min), increase dosing interval to every 24 hours. |
| Liver impairment | Child-Pugh A: no adjustment. Child-Pugh B or C: maximum total daily dose of 8 mg. |
| Pediatric use | Children 6 months to 18 years: 0.15 mg/kg/dose intravenously every 4-8 hours; maximum 8 mg per dose. For prevention of chemotherapy-induced nausea, 0.15 mg/kg/dose 30 minutes before chemotherapy; maximum 24 mg/day. |
| Geriatric use | No specific dose adjustment required; monitor for QT prolongation and electrolyte disturbances. Use with caution in patients over 75 years due to increased risk of adverse effects. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Drugs that prolong the QT interval may have additive effects Can cause QT prolongation and subsequent arrhythmias.
| FDA category | Human |
| Breastfeeding | Small amounts excreted in breast milk; M/P ratio ~0.7. Considered compatible with breastfeeding; monitor infant for sedation. |
| Teratogenic Risk | First trimester: No consistent evidence of major malformations; some studies suggest a slight increase in cleft palate (odds ratio ~1.3). Second/third trimester: No known specific risks. Avoid in first trimester unless necessary. |
■ FDA Black Box Warning
No FDA black box warning.
| Common Effects | Headache |
| Serious Effects |
Hypersensitivity to ondansetron or any component; concurrent use of apomorphine (hypotension and loss of consciousness reported).
| Precautions | Risk of QT interval prolongation (dose-related); avoid in patients with congenital QT syndrome or electrolyte abnormalities; serotonin syndrome when co-administered with other serotonergic drugs; hypersensitivity reactions including anaphylaxis; masked signs of paralytic ileus or gastric distention. |
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| Fetal Monitoring | Monitor for maternal QTc prolongation (ECG if risk factors); assess for extrapyramidal symptoms (rare). Fetal heart rate monitoring not routinely required. |
| Fertility Effects | No known adverse effects on human fertility. |