ondansetron hydrochloride
Zofran, Zofran ODT

Available forms
Available by prescription only
Injection: 2 mg/ml in 20-ml multidose vials, 2-ml single-dose vials
Injection, premixed: 32 mg/50 ml in D₅W single-dose vial
Oral solution: 4 mg/5 ml
Orally disintegrating tablets: 4 mg, 8 mg
Tablets: 4 mg, 8 mg, 24 mg

Indications and dosages
 Prevention of nausea and vomiting caused by initial and repeat courses of emetogenic chemotherapy, including high-dose cisplatin. Adults and children age 4 and older: Three I.V. doses of 0.15 mg/kg with first dose infused over 15 minutes beginning 30 minutes before start of chemotherapy, with subsequent doses of 0.15 mg/kg administered 4 and 8 hours after first dose. In adults, may also administer as a single dose of 32 mg, infused over 15 minutes, 30 minutes before start of chemotherapy.
Adults and children older than age 12: Initially, 8 mg P.O. starting 30 minutes before start of chemotherapy, with a repeat dose after the first dose; then q 12 hours for 1 to 2 days after completion of chemotherapy.
Children ages 4 to 11: Initially, 4 mg given P.O. 30 minutes before start of chemotherapy with subsequent doses 4 and 8 hours after initial dose. Then 4 mg given P.O. q 8 hours for 1 to 2 days after completion of chemotherapy.
 Prevention of radiation-induced nausea and vomiting. Adults: 8 mg P.O. t.i.d. First dose should be 1 to 2 hours before radiation treatment. Patients receiving single, high-dose radiation to abdomen should continue q-8-hour dosing for 1 to 2 days.
 Prevention of postoperative nausea and vomiting. Adults: 16 mg P.O. 1 hour before anesthesia or 4 mg I.V. immediately before anesthesia or soon after operation. Or, 4 mg I.M. undiluted as a single injection.
Children ages 2 to 12 who weigh more than 40 kg (88 lb): 4 mg I.V. as a single dose.
Children ages 2 to 12 who weigh 40 kg or less: 0.1 mg/kg I.V. as a single dose.
≡ Dosage adjustment. For patients with severe hepatic impairment, total daily dose shouldn’t exceed 8 mg.

Pharmacodynamics
Antiemetic action: Not well known. Ondansetron isn’t a dopamine-receptor antagonist. Because serotonin receptors of the 5-HT₃ type occur peripherally on vagal nerve terminals and centrally in the chemoreceptor trigger zone, it’s uncertain if antiemetic action is mediated centrally, peripherally, or both.

Pharmacokinetics
Absorption: Absorption is variable with oral administration; bioavailability is 50% to 60%.
Distribution: 70% to 76% protein-bound.
Metabolism: Extensively metabolized by hydroxylation on the indole ring, followed by glucuronide or sulfate conjugation.
Excretion: 5% recovered in urine as parent compound. Half-life in adults is 3 1/2 to 6 hours.

Contraindications and precautions
Contraindicated in patients hypersensitive to drug. Use cautiously in patients with hepatic failure. Orally disintegrating tablet contains aspartame; use cautiously in patients with phenylketonuria.

Interactions
Drug-herb. Horehound: May enhance serotonergic effects. Discourage use together.

Adverse reactions
CNS: headache, malaise, fatigue, dizziness, sedation, anxiety, agitation, fever, oculogyric crisis.
CV: chest pain, hypotension.
GI: diarrhea, constipation, abdominal pain, xerostomia.
GU: urine retention, gynecologic disorders.
Musculoskeletal: musculoskeletal pain.
Respiratory: hypoxia.
Skin: rash, injection-site reaction.
Other: chills, anaphylaxis.

Effects on lab test results
• May increase ALT and AST levels.

Overdose and treatment
Doses more than 10 times recommended dose have been given without incident.
 If overdose is suspected, manage with supportive therapy.

Special considerations
• Drug may be administered I.V. undiluted over 2 to 5 minutes.
• For infusion, dilute drug in 50 ml of compatible solution and infuse over 15 minutes.
• Ondansetron is stable at room temperature for 48 hours after dilution with normal saline solution, D₅W, 5% dextrose and normal saline solution, 5% dextrose and half-normal saline, or 3% saline.
• Monitor liver function tests if giving repeated doses.
• For patients undergoing abdominal surgery, watch for ileus, gastric distention, or both.
Breast-feeding patients
• It isn’t known if drug appears in breast milk. Use cautiously in breast-feeding women.
Pediatric patients
• Little information is available for use in children age 3 and under for preventing chemotherapy-induced nausea and vomiting, and in children younger than age 2 for preventing postoperative nausea and vomiting.
Geriatric patients
• No age-related problems have been reported.

Patient education
• Advise patient to call if adverse effects occur.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use