How Does It Work?
Alosetron belongs to a group of medications known as 5-HT3 receptor antagonists. It works by blocking the action of a certain chemical in the body known as serotonin (also called 5-HT). It does this by preventing serotonin from binding to receptors known as 5-HT3 receptors. These receptors are located in various parts of the body, including the intestines.
Serotonin has many roles in the body. Most notably, serotonin is involved in mood. However, this important chemical also plays a role in the functioning of the gastrointestinal (GI) tract. When serotonin binds to 5-HT3 receptors in the gut, it regulates the movement of waste through the intestines, the amount of fluid in stool, and our response to pain and discomfort in the stomach.
While the exact cause of IBS is not entirely known, it appears that having too much serotonin may cause food to move through the intestines too quickly (which can cause diarrhea) and increase pain sensitivity. By preventing serotonin from binding to 5-HT3 receptors in the intestines, alosetron can help reduce diarrhea and pain associated with IBS.
Clinical Effects for Alosetron
Alosetron has been studied in several clinical trials. In these studies, the medication was shown to reduce symptoms of IBS in women who had diarrhea as their main IBS symptom. More specifically, 10 to 19 percent more women who received alosetron had adequate relief of abdominal (stomach) pain and discomfort, compared with women who received a placebo (a "sugar pill" with no active ingredient).
In addition, in one study, 43 to 51 percent of women taking alosetron reported moderate to substantial improvements in their IBS symptoms, compared with 31 percent of those taking a placebo.
Alosetron was also shown to increase the number of days women were able to control their bowel urgency (the need to have a bowel movement), to improve stool consistency from loose to formed, and to reduce stool frequency from an average of 3.2 each day to 2.1 each day. However, the medication did not appear to improve the feeling of incomplete emptying of the bowels.