ondansetron hydrochloride

ondansetron hydrochloride

Ondemet (UK), Zofran, Zofran ODT, Zofran Preservative Free

Pharmacologic class: Serotonin type 3 (5-HT₃) antagonist

Therapeutic class: Antiemetic

Pregnancy risk category B

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

Precautions

Use cautiously in:
• hepatic disease
• 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.

Route	Onset	Peak	Duration
P.O., I.V.	Rapid	15-30 min	4-8 hr
I.M.	Rapid	40 min	Unknown

Adverse reactions

CNS: headache, dizziness, malaise, drowsiness, fatigue, weakness, extrapyramidal reactions

CV: chest pain, hypotension

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.

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.
☞ Instruct patient to immediately report extrapyramidal symptoms 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.