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Ondansetron hydrochloride
Ondansetron hydrochloride (Zofran)
Ondansetron hydrochloride
(on-DAN-sih-tron)
Pregnancy Category: B Zofran Zofran ODT (Rx)

Classification: Antiemetic

Action/Kinetics: Cytotoxic chemotherapy is thought to release serotonin from enterochromoffin cells of the small intestine. The released serotonin may stimulate the vagal afferent nerves through the 5-HT₃ receptors, thus stimulating the vomiting reflex. Ondansetron, a 5-HT₃ antagonist, blocks this effect of serotonin. Whether the drug acts centrally and/or peripherally to antagonize the effect of serotonin is not known. Time to peak plasma levels, after PO: 1.7-2.1 hr. t1/2, after IV use: 3.5-4.7 hr; after PO use: 3.1-6.2 hr, depending on the age. A decrease in clearance and increase in half-life are observed in clients over 75 years of age, although no dosage adjustment is recommended. Clients less than 15 years of age show a shortened plasma half-life after IV use (2.4 hr). Significantly metabolized with 5% of a dose excreted unchanged in the urine.

Uses: Parenteral: Prevent N&V; resulting from initial and repeated courses of cancer chemotherapy, including high-dose cisplatin. Prophylaxis and treatment of selected cases of postoperative N&V;, especially situations where there is multiple retching and long periods of N&V.; Oral: Prevention of N&V; due to initial and repeated courses of cancer chemotherapy, including single-day highly emetogenic cancer chemotherapy (e.g. Cisplatin). Prevenion of N&V; associated with radiotherapy in clients receiving either total body irradiation, single high-dose fraction, or daily fractions to the abdomen. Prevention of postoperative N&V.; Investigational: N&V; due to acetaminophen poisoning, acute levodopa-induced psychosis, N&V; due to prostacyclin therapy, spinal or epidural morphine-induced pruritus, social anxiety disorder, decrease in bulimic episodes in clients with bulimia nervosa.

Special Concerns: Use with caution during lactation. Safety and effectiveness in children 3 years of age and younger are not known.

Side Effects: GI: Diarrhea (most common), constipation, xerostomia, abdominal pain. CNS: Headache, dizziness, drowsiness, sedation, malaise, fatigue, anxiety, agitation, extrapyramidal syndrome, clonic-tonic seizures. CV: Tachycardia, chest pain, hypotension, ECG alterations, angina, bradycardia, syncope, vascular occlusive events. Dermatologic: Pain, redness, and burning at injection site; cold sensation, pruritus, paresthesia. Hypersensitivity (rare): Anaphylaxis, bronchospasm, shock SOB, hypotension, angioedema, urticaria. Miscellaneous: Rash, bronchospasm transient blurred vision, hypokalemia, weakness, fever, musculoskeletal pain, shivers, dysuria, postoperative carbon dioxide-related pain, akathisia, acute dystonic reactions, gynecologic disorder, urinary retention, wound problem.

Laboratory Test Alterations: AST, ALT.

Drug Interactions: Rifampin ondansetron plasma levels R/T liver metabolism.

How Supplied: Injection: 2 mg/mL, 32 mg/50 mL; Oral Solution: 4 mg/5 mL; Tablet: 4 mg, 8 mg, 24 mg; Tablets, Orally Disintegrating: 4 mg (as base), 8 mg (as base)

Dosage
•IM, IV Prevention of N&V; due to chemotherapy.
Adults and children, 4-18 years: Three doses of 0.15 mg/kg each. For the 3-dose regimen, the first dose is infused over 15 min starting 30 min before the start of chemotherapy; the second and third doses are given 4 hr and 8 hr, respectively, after the first dose. Alternatively, a single 32-mg dose may be given over 15 min beginning 30 min before the start of chemotherapy.
N&V; postoperatively.
Adults: 4 mg over 2-5 min immediately before induction of anesthesia or postoperatively as needed. Children, 2 to 12 years weighing 40 kg or less: 0.1 mg/kg over 2-5 min. Children, 2 to 12 years weighing over 40 kg: 4 mg over 2-5 min.
•Tablets In clients receiving moderately emetogenic chemotherapy agents.
Adults and children over 12 years of age: 8 mg 30 min before treatment followed by a second 8-mg dose 8 hr after the first dose; then, 8 mg b.i.d. for 1-2 days after chemotherapy. Children, 4-11 years: 4 mg t.i.d. The first dose is given 30 min before chemotherapy with subsequent doses 4 and 8 hr after the first dose. Then 4 mg q 8 hr for 1-2 days after completion of chemotherapy.
In clients receiving single-day highly emetogenic cancer chemotherapy.
Adults: 24 mg once a day given 30 min before the single-day dose..
Prevention of N&V; due to total body irradiation.
8 mg 1-2 hr before each fraction of radiotherapy administered each day.
Prevention of N&V; in single high-dose fraction radiotherapy to the abdomen.
8 mg 1-2 hr before radiotherapy with subsequent doses 8 hr after the first dose for 1-2 days after completion of radiotherapy.
Prevention of N&V; due to daily fractionated radiotherapy to the abdomen.
8 mg 1-2 hr before radiotherapy, with subsequent doses 8 hr after the first dose for each day radiotherapy is given.
Prevention of postoperative N&V.;
Adults: 16 mg given as a single dose 1 hr before induction of anesthesia.