Zofran

Action

Blocks serotonin at 5-HT₃ receptor sites in vagal nerve terminals by disrupting CNS chemoreceptor trigger zone

Availability

Injection: 2 mg/ml in 2- and 20-ml vials

Injection (premixed): 32 mg/50 ml single-dose containers

Injection USP (preservative-free): 2 mg/ml in 2-ml single-dose vials

Oral solution: 4 mg/5 ml

Tablets: 4 mg, 8 mg, 24 mg

Tablets (orally disintegrating): 4 mg, 8 mg

Indications and dosages

➣ To prevent nausea and vomiting caused by moderately emetogenic chemotherapy

Adults and children older than age 12: 8 mg (tablet) or 10 ml (oral solution) P.O. b.i.d.; give first dose 30 minutes before chemotherapy and repeat dose 8 hours later. Give 8 mg (tablet) or 10 ml (oral solution) P.O. q 12 hours for 1 to 2 days after chemotherapy ends.

Children ages 4 to 11: 4 mg (tablet) or 5 ml (oral solution) P.O. q 8 hours; give first dose 30 minutes before chemotherapy and repeat dose 4 and 8 hours later. Give 4 mg (tablet) or 5 ml (oral solution) P.O. q 8 hours for 1 to 2 days after chemotherapy ends.

➣ To prevent nausea and vomiting caused by highly emetogenic chemotherapy

Adults and children older than age 12: 32 mg I.V. as a single dose infused over 15 minutes, starting 30 minutes before chemotherapy; or three 0.15-mg/kg doses I.V., with first dose infused over 15 minutes, starting 30 minutes before chemotherapy and repeated 4 hours and 8 hours later.

➣ To prevent nausea and vomiting caused by radiation

Adults and children older than age 12: 8 mg (tablet) or 10 ml (oral solution) P.O. 1 to 2 hours before radiation and repeated q 8 hours, depending on radiation type, location, and extent

➣ Prevention and treatment of postoperative nausea and vomiting

Adults and children older than age 12: 16 mg (tablet) or 20 ml (oral solution) P.O. 1 hour before anesthesia induction, or 4 mg I.V. or I.M. before anesthesia or postoperatively

Children ages 2 to 12 weighing more than 40 kg (88 lb): 4 mg I.V. before anesthesia or postoperatively

Children ages 2 to 12 weighing less than 40 kg (88 lb): 0.1 mg/kg I.V. before anesthesia or postoperatively

Dosage adjustment

• Hepatic impairment

Contraindications

• Hypersensitivity to drug

• Concurrent use of apomorphine

Precautions

Use cautiously in:

• hepatic disease

• congenital long QT syndrome (avoid use)

• hypersensitivity to other selective 5-HT3 receptor antagonists

• phenylketonuria (with orally disintegrating tablets)

• pregnant or breastfeeding patients

• children younger than age 12.

Administration

• Give first dose before emetogenic event.

• Remove orally disintegrating tablet by peeling back foil with dry hands; don't push tablet through foil backing. After removing, place tablet on patient's tongue, where it will dissolve within seconds. Tell patient to swallow saliva.

• Give undiluted when administering I.M. before anesthesia induction.

• Give undiluted by direct I.V. immediately before anesthesia induction, or postoperatively if nausea and vomiting occur. Administer slowly, over at least 30 seconds (preferably over 2 to 5 minutes).

• For intermittent I.V. infusion, dilute in 50 ml of dextrose 5% in water (D₅W) and normal saline solution or D₅W and half-normal saline solution. Infuse over 15 minutes.

• When giving I.V., don't use flexible plastic container in series connection.

Adverse reactions

CNS: headache, dizziness, malaise, drowsiness, fatigue, weakness, extra-pyramidal reactions

CV: chest pain, hypotension, ECG changes including QT-interval prolongation (rare and mostly with I.V. use), torsades de pointes (postmarketing reports)

GI: constipation, diarrhea, abdominal pain, dry mouth

GU: urinary retention

Respiratory: bronchospasm

Skin: rash

Other: pain at injection site, shivering, anaphylaxis

Interactions

Drug-drug. Drugs that alter hepatic enzyme activity: altered pharmacokinetics of ondansetron

Drug-diagnostic tests. Alanine aminotransferase, aspartate aminotransferase, bilirubin: transient elevations

Patient monitoring

• Monitor GI status.

• Assess for extrapyramidal reactions.

• Check vital signs. Watch for hypotension and bronchospasm.

• Monitor fluid intake and output. Stay alert for urinary retention.

See Be aware that cases of torsades de pointes have been reported. Monitor ECG in patients with electrolyte abnormalities (such as hypokalemia or hypomagnesemia), congestive heart failure, or bradyarrhythmias, and in patients taking other drugs that lead to prolonged QT interval.

See Be aware that using ondansetron after abdominal surgery or with chemotherapy-induced nausea and vomiting may mask a progressive ileus or gastric distention.

Patient teaching

• Tell patient to remove orally disintegrating tablet by peeling back foil with dry hands-not by pushing tablet through foil backing. Instruct him to place tablet on tongue, where it will dissolve within seconds, and then to swallow saliva.

See Instruct patient to immediately report extrapyramidal symptoms, irregular heartbeats, abdominal distention after abdominal surgery, or allergic reaction.

• Inform patient with phenylketonuria (or caregiver) that powder contains phenylalanine.

• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and tests mentioned above.