Zofran (Ondansetron Hydrochloride)

Zofran Review

This medication is used to prevent nausea and vomiting caused by cancer chemotherapy or after surgery. It works by blocking the hormone (serotonin) that causes vomiting.

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Zofran Drug Class and Mechanism

Ondansetron is a selective 5-HT3 receptor antagonist. While its mechanism of action has not been fully characterized, ondansetron is not a dopamine-receptor antagonist. Serotonin receptors of the 5-HT3 type are present both peripherally on vagal nerve terminals and centrally in the chemoreceptor trigger zone of the area postrema. It is not certain whether ondansetron’s antiemetic action is mediated centrally, peripherally, or in both sites. However, cytotoxic chemotherapy appears to be associated with release of serotonin from the enterochromaffin cells of the small intestine. In humans, urinary 5-HIAA (5-hydroxyindoleacetic acid) excretion increases after cisplatin administration in parallel with the onset of emesis. The released serotonin may stimulate the vagal afferents through the 5-HT3 receptors and initiate the vomiting reflex.

Zofran Uses

Although it is highly effective, its high cost had limited its use to controlling PONV and CINV- although it is now available in cheaper generic forms. It is also used off-label to treat hyperemesis gravidarum in pregnant women, but there is no conclusive data available on its safety in pregnancy, especially during the first trimester. It is also often used to treat cyclic vomiting syndrome; although there have been no formal trials to confirm efficacy, case reports suggest it can be helpful in some cases. The drug is administered 1–3 times daily, depending on the severity of nausea and/or vomiting. The normal oral dose for adults and children over the age of 12, is 8 mg initially, followed by a second dose of 8 mg, eight hours later. The drug is then administered once every 12 hours, usually not for more than 2-3 days. Following oral administration, it takes about 1.5–2 hours to reach maximum plasma concentrations. This drug is removed from the body by the liver and kidneys.

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Zofran Side Effects

Diarrhea or constipation, headache, lightheadedness or drowsiness (uncommon), as well as blurred vision may occur. If these effects persist or worsen, notify your doctor promptly. Very unlikely but report promptly: chest pain. In the unlikely event you have an allergic reaction to this drug, seek immediate medical attention. Symptoms of an allergic reaction include: rash, itching, swelling, severe dizziness, trouble breathing. If you notice other effects not listed above, contact your doctor or pharmacist.

Zofran Pregnancy

Teratogenic Effects: Pregnancy Category B. Reproduction studies have been performed in pregnant rats and rabbits at daily oral doses up to 15 and 30 mg/kg/day, respectively, and have revealed no evidence of impaired fertility or harm to the fetus due to ondansetron. There are, however, no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed.

Zofran Overdose

There is no specific antidote for ondansetron overdose. Patients should be managed with appropriate supportive therapy. Individual intravenous doses as large as 150 mg and total daily intravenous doses as large as 252 mg have been inadvertently administered without significant adverse events. These doses are more than 10 times the recommended daily dose. In addition to the adverse events listed above, the following events have been described in the setting of ondansetron overdose: “Sudden blindness” (amaurosis) of 2 to 3 minutes' duration plus severe constipation occurred in 1 patient that was administered 72 mg of ondansetron intravenously as a single dose. Hypotension (and faintness) occurred in a patient that took 48 mg of ZOFRAN Tablets. Following infusion of 32 mg over only a 4-minute period, a vasovagal episode with transient second-degree heart block was observed. In all instances, the events resolved completely.

Zofran More Information

Ondansetron is a well-tolerated drug with few side effects. Headache, constipation, and dizziness are the most commonly reported side effects associated with its use. There have been no significant drug interactions reported with this drug's use. It is broken down by the hepatic cytochrome P450 system and it has little effect on the metabolism of other drugs broken down by this system.