Ondansetron (INN) (a.k.a. Zofran) is a serotonin 5-HT3 receptor antagonist used mainly as an antiemetic to treat nausea and vomiting following chemotherapy. Its effects are thought to be on both peripheral and central nerves. One part is to reduce the activity of the vagus nerve, which is a nerve that activates the vomiting center in the medulla oblongata, the other is a blockage of serotonin receptors in the chemoreceptor trigger zone. It does not have much effect on vomiting that is due to motion sickness. This drug does not have any effect on dopamine receptors or muscarinic receptors. 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. It is currently marketed by GlaxoSmithKline (GSK) under the trade name Zofran; other manufacturers include Cipla Ltd. (Emeset), Gedeon Richter Ltd. (Emetron), Korea United Pharmaceuticals (Emodan) and Zentiva a.s. (Ondemet). On May 29, 2006, Baxter Healthcare received tentative approval [1] to market its own label of Ondansetron Injection, USP, 8 mg/50 mL and 32 mg/50 mL iso-osmotic sodium chloride solution, after GSK's patent expired on December 24, 2006.