A 5-HT3 antagonist used for the management of severe diarrhea-predominant irritable bowel syndrome (IBS) in women only.

Lotronex is trade name.

Pregnancy category US: B (No risk)

Oral agent.

Bioavailability 50–60%

Protein binding 82%.

Metabolism- Hepatic, including CYP2C9, CYP3A4 and CYP1A2.

Elimination half-life 1.5–1.7 hours.

Excretion Renal 73%, faecal 24%.

Indicated only for women with severe diarrhea-predominant irritable bowel syndrome (IBS-D) who have:

chronic IBS symptoms

had anatomic or biochemical abnormalities of the gastrointestinal tract excluded

not responded adequately to conventional therapy.

Severe IBS-D includes: diarrhea and 1 or more of the following:

frequent and severe abdominal pain/discomfort

frequent bowel urgency or fecal incontinence

disability or restriction of daily activities due to IBS

Should not be initiated in patients with constipation.

Associated with the risk of developing ischemic colitis and serious complications of constipation.

Contraindications include: history of chronic or severe constipation or sequelae from constipation; intestinal obstruction, stricture, toxic megacolon, gastrointestinal perforation, and/or adhesions, ischemic colitis, impaired intestinal circulation, thrombophlebitis, or hypercoagulable state, Crohn’s disease or ulcerative colitis, diverticulitis, severe hepatic impairment.

Concomitant use of fluvoxamine is a contraindication.

In a phase III trial 1 mg alosetron, taken orally twice daily for 12 weeks, was associated with a 12% improvement in relief from abdominal pain and discomfort associated with diarrhea-predominant patients.

Currently approved dosage in the U.S. at 0.5 and 1 mg.

The cumulative incidence of ischemic colitis was 2 in 1000, while serious complications arising from constipation such as obstruction, perforation, impaction, toxic megacolon, secondary colonic ischaemia, and death was 1 in 1000.

Has an antagonist action on the 5-HT3 receptors of the enteric nervous system of the gastrointestinal tract, but it is not classified or approved as an antiemetic.

Stimulation of 5-HT3 receptors is positively correlated with gastrointestinal motility, alosetron’s 5-HT3 antagonism slows the movement of fecal matter through the large intestine, increasing the extent to which water is absorbed, and decreasing the moisture and volume of the remaining waste products

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