Ondansetron
Mechanism :
Ondansetron is a selective 5-HT3 receptor antagonist. While its mechanism of action has not been fully characterized, ondansetron is not a dopamine-receptor antagonist. Serotonin receptors of the 5-HT3 type are present both peripherally on vagal nerve terminals and centrally in the chemoreceptor trigger zone of the area postrema. It is not certain whether ondansetron antiemetic action is mediated centrally, peripherally, or in both sites.
Indication :
- Chemotherapy induced nausea and vomiting
- Post-operative nausea and vomiting
Contraindications :
Contraindicated for patients known to have hypersensitivity to the drug.
Dosing :
Nausea and vomiting chemotherapy induced:
Oral:
4-12 years: 4 mg started half hour before chemotherapy, then 4 and 8 hours after first dose, then 3 times a day for 1-2 days after chemotherapy.
>12 years: 8 mg started half hour before chemotherapy, then 2 times a day for 1-2 days after chemotherapy or a single dose of 24 mg.
IV:
>6 months: 0.15 mg/kg over 15 mins, given half hour before chemotherapy, then 4 and 8 hours after first dose. Max: 16 mg per dose.
Post-op nausea and vomiting:
Give slow IV slow infusion.
1 month-12 years: 0.1 mg/kg in <40 kg and 4 mg in >40 kg.
12-18 years: 4 mg before anaesthesia or after procedure (IV/IM)
OR, 16 mg 1 hour before anesthesia orally.
Adverse Effect :
Commonly reported adverse reactions include headache, malaise, fatigue, constipation and diarrhea.
Interaction :
Phenytoin, Carbamazepine, and Rifampicin: The clearance of ondansetron was significantly increased, and ondansetron blood concentrations were decreased.
Renal Dose :
Dose in Renal Impairment GFR (mL/min)
20-50 | Dose as in normal renal function |
10-20 | Dose as in normal renal function |
<10 | Dose as in normal renal function |
Dose in Patients undergoing Renal Replacement Therapies
CAPD | Unlikely to be dialysed. Dose as in normal renal function |
HD | Not dialysed. Dose as in normal renal function |
HDF/High flux | Unknown dialysability. Dose as in normal renal function |
CAV/VVHD | Unknown dialysability. Dose as in normal renal function |
Hepatic Dose :
Per the manufacturer, ondansetron dosage should not exceed 8 mg/day IV or PO in adult patients with severe hepatic impairment. In such patients, plasma clearance is reduced, resulting in a dramatically prolonged elimination half-life. No specific pediatric recommendations are available.
Severe hepatic impairment
IV dosing on day 1: 0.075mg/kg/dose Maximum dose being 4mg for children 2-11y and 8 mg/dose in children greater than 12 years of age.
Oral dosing: for Infants and Children of ages 6 months to 10 years
8 to 15 kg: 1 mg/dose once
>15 to 30 kg: 2 mg/dose once
>30 kg: 4 mg/dose once