Zofran: A Serotonin Blocker

            Chemotherapy induced nausea and vomiting, CINV, has been a significant problem with oncology patients over past years. As a result much research was done and has lead to the creation of Zofran (Bernstein and Ong 2002). Ondansetron, marketed as Zofran was the first of its kind; it is a serotonin 5-HT3 receptor blocker, otherwise know as an antiemetic agent. Ondansetron is a tremendous breakthrough and is much more effective than older antiemetics, in some cases by almost 50% (Ramsook 2002). Ondansetron was FDA approved in January 1991 as a treatment for chemotherapy-induced nausea and vomiting with parenteraly administered dosage. It was later approved in oral dosage forms as a treatment for post-operative nausea and vomiting in April 1995. In 1999 ondansetron was approved for use as an "orally disintegrating tablet," Zofran ODT┬«. This form of ondansetron does not require water to assist in swallowing (Clinical Pharmacology 2002). Now ondansetron is used primarily as a treatment for chemotherapy-induce and post-operative nausea and vomiting; however, it is also being recently used to treat drug dependencies such as alcoholism and to treat gastrointestinal disorders such as acute gastroenteritis.

             Ondansetron blocks the serotonin 5-HT3 receptors centrally and peripherally. 5-HT3 receptors are found centrally in the chemoreceptor trigger zone and peripherally in the lining of the small intestines. Most emesis, often associated with chemotherapy and/or radiation therapy, appears to be connected with the release of serotonin 5-HT3 from enterochromaffin cells that line the small intestine walls. By blocking these nerves signals to the central nervous system can no longer be sent. Ondansetron has also been identified as a small combatant of the serotonin 5-HT4 receptor (Physician's Desk Reference 1993). Research is continuing to be done on what other agents ondansetron combats and if its action is mediated centrally or peripherally.

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