Last reviewed 2026-04-20 · How we verify

Lotronex (ALOSETRON)

Lotronex works by blocking serotonin receptors in the gut to slow down bowel movements.

Lotronex (ALOSETRON) is a serotonin-3 receptor antagonist developed by PROMETHEUS LABS and currently owned by Legacy Pharma. It targets the 5-hydroxytryptamine receptor 3A to treat irritable bowel syndrome with diarrhea. Lotronex is a small molecule with a half-life of 1.6 hours and bioavailability of 55%. It is off-patent and has multiple generic manufacturers. Key safety considerations include its potential for serious side effects such as constipation and severe complications.

At a glance

Mechanism of action

Alosetron is potent and selective 5-HT3 receptor antagonist. 5-HT3 receptors are ligand-gated cation channels that are extensively distributed on enteric neurons in the human gastrointestinal tract, as well as other peripheral and central locations. Activation of these channels and the resulting neuronal depolarization affect the regulation of visceral pain, colonic transit, and gastrointestinal secretions, processes that relate to the pathophysiology of IBS. 5-HT3 receptor antagonists such as alosetron inhibit activation of non-selective cation channels, which results in the modulation of the enteric nervous system. The cause of IBS is unknown. IBS is characterized by visceral hypersensitivity and hyperactivity of the gastrointestinal tract, which lead to abnormal sensations of pain and motor activity. Following distention of the rectum, patients with IBS exhibit pain and discomfort at lower volumes than healthy volunteers. Following such distention, alosetro

Approved indications

• Irritable bowel syndrome with diarrhea

Boxed warnings

• WARNING: SERIOUS GASTROINTESTINAL ADVERSE REACTIONS Infrequent but serious gastrointestinal adverse reactions have been reported with the use of alosetron tablets. These events, including ischemic colitis and serious complications of constipation, have resulted in hospitalization, and rarely, blood transfusion, surgery, and death. Alosetron tablets are indicated only for women with severe diarrhea-predominant irritable bowel syndrome (IBS) who have not responded adequately to conventional therapy [see Indications and Usage (1)] . Alosetron tablets should be discontinued immediately in patients who develop constipation or symptoms of ischemic colitis. Patients should immediately report constipation or symptoms of ischemic colitis to their prescriber. Alosetron tablets should not be resumed in patients who develop ischemic colitis. Patients who have constipation should immediately contact their prescriber if the constipation does not resolve after alosetron tablets is discontinued. Patients with resolved constipation should resume alosetron tablets only on the advice of their treating prescriber [see Dosage and Administration (2.1) , Warnings and Precautions (5.1) , (5.2)]. WARNING: SERIOUS GASTROINTESTINAL ADVERSE REACTIONS See full prescribing information for complete boxed warning. Infrequent but serious gastrointestinal adverse reactions have been reported with the use of alosetron tablets. These events, including ischemic colitis and serious complications of constipation, have resulted in hospitalization and, rarely, blood transfusion, surgery, and death. Alosetron tablets are indicated only for women with severe diarrhea-predominant irritable bowel syndrome (IBS) who have not responded adequately to conventional therapy. ( 1 ) Discontinue alosetron tablets immediately in patients who develop constipation or symptoms of ischemic colitis. Do not resume alosetron tablets in patients who develop ischemic colitis. ( 2.1 , 5.1 , 5.2 )

Common side effects

• Constipation
• Abdominal discomfort and pain
• Nausea
• Gastrointestinal discomfort and pain
• Abdominal distention
• Regurgitation and reflux
• Hemorrhoids
• Diarrhea
• Flatulence
• Abdominal pain
• Hemorrhoidal hemorrhage
• Fatigue

Drug interactions

• fluvoxamine
• ketoconazole

Key clinical trials

• Safety and Efficacy Study of GR68755 (Alosetron Hydrochloride) to Treat Severe Diarrhea-Predominant Irritable Bowel Syndrome (IBS) (PHASE2)
• Study to Assess the Effect Of Alosetron On Mucosal Blood Flow (PHASE4)
• Study In Women With Severe Diarrhea-Predominant Irritable Bowel Syndrome Having Failed Conventional Therapy (PHASE3)
• Study Of Women With Severe Diarrhea-Predominant Irritable Bowel Syndrome Having Failed Conventional Therapy (PHASE3)
• LOTRONEX® in Severe Diarrhea-Predominant Irritable Bowel Syndrome (IBS-D)

Primary sources

Every claim on this page is sourced from regulatory or scientific primary sources. See our editorial policy for full methodology.

Competitive intelligence

For the full competitive landscape — auto-detected comparators, recent regulatory actions across the set, upcoming PDUFA, patent timeline, sponsor landscape:

• Lotronex CI brief — competitive landscape report
• Lotronex updates RSS · CI watch RSS
• Legacy Pharma portfolio CI