Ondansetron

Ondansetron (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 Gedeon Richter Ltd. (Emetron), 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.

Ondansetron may also be used in treating schizophrenia, parkinsons and alcoholism.

History

Ondansetron was developed around 1984 by scientists working at Glaxo's laboratories in London. After several attempts the company successfully filed for U.S. patent protection for the drug in 1986. U.S. Patent 4,695,578 was granted in September 1987 while U.S. Patent 4,753,789 was granted in June 1988. U.S. Patent 5,578,628, a divisional patent of U.S. Patent 4,753,789, was granted in November 26, 1996. Ondansetron was granted Food and Drug Administration (FDA) approval as Zofran in January 1991. Glaxo did pediatric research on Zofran's uses, and gained patent extension as a result. Consequently U.S. exclusivity ended December 24, 2006. The FDA subsequently approved the first generic versions in December 2006, with marketing approval granted to Teva Pharmaceuticals USA and SICOR Pharmaceuticals.

Clinical uses

See also: 5-HT3 antagonist

The 5-HT₃ receptor antagonists are the primary drugs used to treat and prevent chemotherapy-induced nausea and vomiting (CINV). Many times they are given intravenously about 30 minutes before beginning therapy. Ondansetron is also effective in controlling post-operative (PONV) and post-radiation nausea and vomiting, and is a possible therapy for nausea and vomiting due to acute or chronic medical illness or acute gastroenteritis.

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 clinical effect of ondansetron (and other drugs from the same group) can be potentiated by combining it with dexamethasone.

Investigational

Schizophrenia

A 2006 tardive dyskinesia in people with schizophrenia, and the study patients also showed significant improvement in the disease's symptoms.^[2][3]

Parkinson's disease

Early studies have also examined ondansetron as a possible treatment for psychosis resulting from advanced Parkinson's disease.^[4] Its ability to be of benefit despite lacking any significant antagonistic properties at 5-HT2A receptor raises interesting questions about the etiology of psychosis.

Alcoholism

Ondansetron lowers the cravings for alcohol, especially in early-onset alcoholics. In one cognitive-behavioral therapy study, ondansetron patients with early-onset alcoholism had fewer drinks per day and reported more days without drinking at all, compared to the other groups in the study. ^[5][6]

Adverse effects

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.

See also

• Granisetron
• Dolasetron
• Alosetron (not an antiemetic but another 5-HT₃ antagonist investigated for controlling irritable bowel syndrome)

References

• Katzung, Bertram G. Basic and Clinical Pharmacology, 9th ed. (2004). ISBN 0-07-141092-9
• United States Patent & Trademark Office patent numbers:
  • U.S. Patent 4,695,578 
  • U.S. Patent 4,753,789 
  • U.S. Patent 5,578,628 
• NDA by Baxter Healthcare Corp.

Notes