In the U.S.—

• Serotonin antagonist
• Irritable bowel syndrome therapy agent

Alosetron (a-LOE-se-tron) is a medicine used to treat irritable bowel syndrome (IBS) in women who have diarrhea as their main symptom. IBS has been called by many names, including irritable colon and spastic colon. IBS is a medical condition causing cramping abdominal pain, abdominal discomfort, urgency (a sudden need to have a bowel movement), and irregular bowel habits, such as diarrhea and constipation. It is not clear why some people develop IBS. It may be caused by your body's overreaction to a body chemical called serotonin. This overreaction may cause your intestinal system to be overactive. Alosetron works by blocking the action of serotonin on the intestinal system. This reduces the cramping abdominal pain, abdominal discomfort, urgency, and diarrhea caused by IBS. Alosetron does not cure IBS and it may not help every person who takes it.

Alosetron is available through a restricted marketing program. The restricted marketing program is because of serious bowel side effects seen with the use of this medication. Only doctors enrolled in the prescribing program for alosetron can write a prescription. No telephone, facsimile, or computerized prescriptions are permitted with this program. Each prescription order must be original with a special sticker attached. Alosetron is available in the following dosage forms:

Oral
• Tablets (U.S.)

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For alosetron, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to alosetron. Also, tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy—Alosetron has not been studied in pregnant women. However, alosetron has not been shown to cause birth defects or other problems in animal studies.

Breast-feeding—It is not known whether alosetron passes into human breast milk. Although most medicines pass into breast milk in small amounts, many of them may be used safely while breast-feeding. Mothers who are taking this medicine and who wish to breast-feed should discuss this with their doctor.

Children—Studies on this medicine have been done only in adult patients, and there is no specific information comparing use of alosetron in children with use in other age groups.

Older adults—Older adults or adults weak from an illness may be especially sensitive to the effects of alosetron. This may increase the chance of serious constipation problems.

• Constipation or
• Crohn's disease or
• Diverticulitis or
• Excessive blood clotting problems or
• Intestinal blood circulation problems or
• Intestinal adhesions, obstructions, perforations, or strictures or
• Ischemic colitis or
• Thrombophlebitis or
• Toxic megacolon or
• Ulcerative colitis

Read the Medication Guide before starting alosetron for the first time and each time you refill your alosetron prescription.

Your doctor will ask you to sign a Patient-Physician Agreement after you have read the Medication Guide for the first time. Signing the agreement means that you understand the risks and benefits of alosetron therapy and that you have read and understand the Medication Guide.

Do not start taking alosetron if you are constipated.

This medicine may be taken with or without food.

If constipation develops while your are taking alosetron, stop taking alosetron and check with your doctor.

Dosing—

The dose of alosetron may be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of alosetron. If your dose is different, do not change it unless your doctor tells you to do so.

The number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are taking alosetron.

• For oral dosage form (tablets):
  • For irritable bowel syndrome associated with diarrhea:
    • Adults—1 milligram (mg) once daily for 4 weeks to see how alosetron affects you. Your doctor will decide if you should continue to take alosetron and how much you should take.
    • Children—Use and dose must be determined by your doctor.

Missed dose—

If you miss a dose of this medicine, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage—

To store this medicine:

• Keep out of the reach of children.
• Do not store in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Keep the medicine from freezing. Do not refrigerate.
• Do not keep outdated medicine or medicine no longer needed. Ask your health care professional how you should dispose of any medicine you do not use. Be sure that any discarded medicine is out of the reach of children.

It is very important that your doctor check you at regular visits .

Stop taking alosetron and check with your doctor right away if you become constipated or have symptoms of poor blood flow to your intestines (ischemic colitis), such as new or worsening abdominal pain, bloody diarrhea, or blood in the stool.

Check with your doctor again if the constipation does not resolve after stopping alosetron.

Do not start taking alosetron again unless your doctor tells you to do so.

Stop taking alosetron and check with your doctor if alosetron does not adequately control irritable bowel syndrome (IBS) symptoms after 4 weeks of taking alosetron.

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur:

• More Common
  • Constipation 
  
  

• Rare
  • Bloody diarrhea;  new or worsening stomach pain or discomfort;  rectal bleeding 
  
  

• Frequency not determined
  • abdominal or stomach pain, cramping, or burning;  black, tarry stools;  diarrhea;  fever;  heartburn;  indigestion;  nausea;  vomiting with or without blood or material that looks like coffee grounds 
  
  

Get emergency help immediately if any of the following symptoms of overdose occur:

• Symptoms of Overdose
  • Clumsiness, unsteadiness, trembling, or other problems with muscle control or coordination;  convulsions (seizures);  difficulty breathing;  shakiness and unsteady walk;  withdrawn or socially detached behavior  
  
  

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. However, check with your doctor if any of the following side effects continue or are bothersome:

• Less Common or Rare
  • Bleeding after defecation;  full or bloated feeling;  swelling of abdominal or stomach area;  pressure in the stomach;  uncomfortable swelling around anus 
  
  

• Frequency not determined
  • Headache;  skin rash 
  
  

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.