Odansetron (Zofran)

A selective serotonin 5-HT3 receptor antagonist.

Trade name Zofran

Category B in pregnancy,

Routes of are administration oral, rectal, IV, IM

Bioavailability ~60%

Protein binding 70%-76%

Metabolism is by Liver enzymes CYP3A4, CYP1A2, CYP2D6

Biological half-life 5.7 hours

Excretion by the kidney.

A medication used to prevent nausea and vomiting caused by cancer chemotherapy, radiation therapy, or surgery.

Useful in gastroenteritis.

Has little effect on vomiting caused by motion sickness.

It can be given by mouth, by injection into a muscle or into a vein.

Common side effects include diarrhea, headache, sleepiness, itchiness, and headaches.

Serious side effects include QT prolongation and severe allergic reaction.

Appears to be safe during pregnancy but has not been well studied.

Does not have any effect on dopamine receptors or muscarinic receptors.

Rarely associated with an increase QT interval and risk for serotonin syndrome.

It is available as a generic medication.

The 5-HT3 receptor antagonists are the primary drugs used to treat and prevent chemotherapy-induced nausea and vomiting and radiotherapy-induced nausea and vomiting.

A number of medications including ondansetron appear to be effective in controlling postoperative nausea and vomiting. It is more effective than metoclopramide, and less sedating than cyclizine or droperidol.

Used off-label to treat morning sickness and hyperemesis gravidarum of pregnancy.

It is activated by serotonin when alcohol is consumed, and this receptor this causes releade of dopamine in the meso cortical limbic region of the brain.

During pregnancy is not associated with a significantly increased risk of spontaneous abortion, stillbirth, major birth defect, preterm birth, low birth weight, or small for gestational age.

Some studies concluded that there is an increase in major congenital malformations due to an increase in heart problems among the babies.

Ondansetron is in pregnancy category B in the US.

Use of ondansetron to reduce vomiting associated with gastroenteritis and dehydration.

Not necessary to adjust the dosage for elderly patients under 75 years of age.

Maximum recommended dose for patients with severe liver function impairment is 8 mg/day.

In these patients, it is cleared from the body at half to one-third the rate as in healthy patients.

C be used for patients with early onset alcohol use disorder, reducing drinks per day, as well as increasing abstinence, but only in patients less than age 25.

Constipation, diarrhea, dizziness, and headache are the most commonly reported side effects.

It is broken down by the hepatic cytochrome P450 system.

Associated with prolongation of the QT interval, which can lead to torsades de pointes.

Prolongation of the QT interval risk is most likely with the intravenous form of the drug, and increases with dose.

The risk is also higher in patients taking other medicines that prolong the QT interval, as well as in patients with congenital long QT syndrome, congestive heart failure, and/or bradyarrhythmias.

Single doses of injectable ondansetron should not exceed 16 mg at one time.

Oral dosing recommendations remain intact, including the recommendation of a single 24-mg oral dose when indicated.

Electrolyte imbalances should be corrected before the use of injectable ondansetron.

No specific treatment is available for ondansetron overdose.

A highly specific and selective serotonin 5-HT3 receptor antagonist, with low affinity for dopamine receptors.

The 5-HT3 receptors are present both peripherally on vagal nerve terminals and centrally in the chemoreceptor trigger zone of the area postrema.

Serotonin is released by the enterochromaffin cells of the small intestine in response to chemotherapeutic agents and may stimulate vagal afferents via 5-HT3 receptors initiating the vomiting reflex.

Antiemetic action may be mediated centrally, peripherally, or in both sites.

Zofran 32mg single IV dose should be avoided due to the risk of a QT interval prolongation, which can lead to Torsades de Pointes, a potentially fatal heart rhythm.


It is useful in treating antipsychotic-induced tardive dyskinesia in people with schizophrenia.


Recommended IV dose maximum of 16 mg per dose.

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