• Pharmacy Author:
    Omudhome Ogbru, PharmD

    Dr. Ogbru received his Doctorate in Pharmacy from the University of the Pacific School of Pharmacy in 1995. He completed a Pharmacy Practice Residency at the University of Arizona/University Medical Center in 1996. He was a Professor of Pharmacy Practice and a Regional Clerkship Coordinator for the University of the Pacific School of Pharmacy from 1996-99.

  • Medical and Pharmacy Editor: Jay W. Marks, MD
    Jay W. Marks, MD

    Jay W. Marks, MD

    Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

What is alosetron, and how does it work (mechanism of action)?

Alosetron is used to treat diarrhea and abdominal discomfort that occurs in some women with irritable bowel syndrome (IBS). It works in a similar fashion as granisetron (Kytril), ondansetron (Zofran) and dolasetron (Anzemet) that are used for preventing nausea and vomiting. The discomfort and diarrhea of IBS is believed to be due to abnormal activity of the muscles of the intestines and/or the nerves that control the muscles. One of the chemical messengers which is important in coordinating the activity of intestinal nerves is serotonin. (Chemical messengers are chemicals produced and released by nerve cells that and cause changes in the activity of other nerve cells.) Alosetron belongs to a class of drugs that block one type of serotonin receptor called the 5-HT3 receptor. Serotonin and its receptors in the intestines may control pain sensation, contraction of intestinal muscle, and release of fluid into the intestines. These actions of serotonin can result in pain and diarrhea. The exact cause of IBS is unknown, but it is thought that stimuli such as food, medications, hormonal changes, or stress may trigger an excessive release or excessive response to serotonin. This may cause pain, and diarrhea seen in patients with diarrhea-predominant IBS. Alosetron, by blocking 5-HT3 receptors, reduces the actions of serotonin. Alosetron (Lotronex) was approved for marketing by the FDA in February, 2000 but was withdrawn from the market in November 2000, because of serious, life-threatening, gastrointestinal side effects. In June 2002, it was approved again by the FDA for marketing but in a restricted manner as part of a drug company-sponsored program for managing the risks associated with treatment. Use of alosetron is allowed only among women with severe, diarrhea-predominant IBS who have failed to respond to conventional treatment for IBS.

What brand names are available for alosetron?


Is alosetron available as a generic drug?


Do I need a prescription for alosetron?


What are the side effects of alosetron?

The most common side effect with alosetron is constipation. One-quarter to one-third of patients may develop this side effect. Severe constipation or intestinal inflammation caused by poor circulation of blood (ischemic colitis) are rare but life-threatening, may require surgery, and may cause death. Therefore, alosetron must be discontinued immediately, and immediate medical attention should be sought if constipation or the signs of ischemic colitis (rectal bleeding or a sudden worsening of abdominal pain) occur.

Other important but less common side effects include:

What is the dosage for alosetron?

The starting dose is 0.5 mg twice daily. If constipation develops at this dose alosetron should be discontinued until the constipation resolves. It may be restarted at 0.5 mg once daily. If 0.5 mg once daily causes constipation, then alosetron should be discontinued. After 4 weeks, patients whose symptoms are not adequately controlled may receive up to 1 mg twice daily. Patients without adequate control after 4 weeks of treatment with 1 mg twice daily should discontinue alosetron. Alosetron may be taken with or without food.

Is alosetron safe to take if I'm pregnant or breastfeeding?

It is not known if alosetron is excreted in breast milk. Therefore, it should be used cautiously by nursing mothers.

What else should I know about alosetron?

What preparations of alosetron are available?

Tablet: 0.5 and 1 mg.

How should I keep alosetron stored?

Tablets should be stored at room temperature, 15 C to 30 C (59 F to 86 F).


Alosetron (Lotronex) is a drug prescribed for the treatment of severe-predominant IBS among women who suffer from chronic IBS symptoms lasting longer than 6 months, and have not responded to conventional IBS treatment. Side effects, drug interactions, dosage, and pregnancy safety information should be reviewed prior to taking this drug.

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See more info: alosetron on RxList
Reference: FDA Prescribing Information