Alosetron, marketed under the brand name Lotronex, is a 5-HT3 antagonist used for the management of severe diarrhea-predominant irritable bowel syndrome (IBS) in women only. Alosetron is a potent and selective 5-HT3 receptor antagonist. 5-HT3 receptors are nonselective 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 irritable bowel syndrome (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. Alosetron is used for the treating women with severe irritable bowel syndrome (IBS) accompanied by severe diarrhea (usually lasting for 6 months or more). It is only prescribed to women who do not respond to other medicines and is not to be used by women whose main IBS problem is constipation.

LIBRAX® combines in a single capsule formulation the antianxiety action of chlordiazepoxide hydrochloride and the anticholinergic/spasmolytic effects of clidinium bromide. Chlordiazepoxide hydrochloride is a versatile, therapeutic agent of proven value for the relief of anxiety and tension. It is indicated when anxiety, tension or apprehension are significant components of the clinical profile. It is among the safer of the effective psychopharmacologic compounds. Clidinium bromide is a synthetic anticholinergic agent which has been shown in experimental and clinical studies to have a pronounced antispasmodic and antisecretory effect on the gastrointestinal tract. It inhibits muscarinic actions of acetylcholine at postganglionic parasympathetic neuroeffector sites. LIBRAX® is indicated to control emotional and somatic factors in gastrointestinal disorders. It may also be used as adjunctive therapy in the treatment of peptic ulcer and in the treatment of the irritable bowel syndrome (irritable colon, spastic colon, mucous colitis) and acute enterocolitis.

Dicyclomine is an anticholinergic tertiary amine used frequently by oral and parenteral route as an effective anti-spasmodic agent. Dicyclomine hydrochloride salt is approved under brand name bentyl for the treatment of functional bowel/irritable bowel syndrome. In addition is known, that dicyclomine is also used in morning and motion sickness, dysmenorrheal, intestinal hypermotility. It was shown, that Dicyclomine is a selective M1 and M3 muscarinic receptors antagonist, but os shown pharmacological activity via the M1 receptor.

AstraZeneca (formerly Astra) is developing robalzotan (NAD-299, AZD-7371), a 5-HT1A antagonist, for the potential treatment of depression and anxiety. The compound has entered phase II trials but was discontinued. Then it investigated for the treatment of irritable bowel syndrome, but the study was prematurely terminated. The same final has expected the development of robalzotan in phase II to treat overactive bladder, this investigation was terminated in July 2005.

Dexverapamil (R-verapamil) is an enantiomer of verapamil. R-isomer behaved as an inhibitor of multidrug-resistant protein MRP1 (involved in the cancer cell multidrug resistance phenotype). It was developed by Knoll (BASF Pharma) as a chemosensitiser and/or modulator of multidrug resistance for use in combination with cancer chemotherapy. Dexverapamil was undergoing phase II clinical studies in France, Italy, Spain, United Kingdom and the US in patients with various cancers. It was also undergoing phase I clinical trials in Japan where it was licensed to Mitsui and Mitsui Toatsu Chemicals. However, development was discontinued. Dexverapamil (R-verapamil) has been developing by AGI therapeutics for the treatment of Irritable bowel syndrome however development was discontinued.

Dextofisopam, a non-serotonergic agent currently being evaluated for the treatment of irritable bowel syndrome (IBS), is the R-enantiomer of racemic tofisopam, a molecule marketed and used safely outside the United States for over three decades for multiple indications including IBS. Dextofisopam represents a novel, first-in-class opportunity with a positive proof-of-concept study in an arena where there are few compounds with unique approaches or positive efficacy results. By structure, Dextofisopam is a member of the homophthalazine class; Dextofisopam binds to specific receptors in areas of the brain affecting autonomic function, including gastrointestinal (GI) function. Unlike the two 5-HT3 or 5-HT4 mediated IBS therapies currently available, both with significant safety concerns, Dextofisopam novel non-serotonergic activity offers a unique and innovative approach to IBS treatment. Recent studies have indicated that dextofisopam binds to a novel binding site within the central nervous system that may be responsible for mediating its actions. This receptor has been characterized as the 2,3-benzodiazepine receptor, which is distinct from the classical 1,4 or 1,5-benzodiazepine receptor. Dextofisopam has no significant binding at other receptors or ion channels

AV608, a 4-aminopiperidine derivative, is a selective, specific, long-acting, orally active and potent nonpeptidic antagonist of the NK-1 receptor. AV-608 had been in phase II clinical trials for the treatment of social phobia and overactive bladder (OAB). This compound was originally discovered by Novartis, and then licensed to Areva Pharmaceuticals in October 2003. Addition this drug was in phase I clinical trial for the treatment of Irritable Bowel Syndrome (IBS), this disease is characterized by chronic abdominal pain and frequent comorbid anxiety. The substance P ⁄ neurokinin-1 receptor system is implicated in the regulation of both pain and anxiety, suggesting a potential therapeutic target in IBS. However, the researches on this drug candidate were discontinued in 2010.

LX-1031, being developed by Lexicon Pharmaceuticals, is an oral, small-molecule tryptophan 5-hydroxylase (TPH) inhibitor that reduces 5-HT synthesis peripherally. LX-1031 is being developed for the potential treatment of diarrhea-predominant irritable bowel syndrome (IBS-D), which is characterized by excess 5-HT. In preclinical studies, LX-1031 dose-dependently reduced expression of 5-HT in the duodenum, jejunum and ileum, but had no effect on brain 5-HT levels. It was in Phase 2 clinical trial, but later development of LX-1031 was discontinued.

Fedotozine [(1R)-1-phenyl-1-[(3,4,5-trimethoxy) benzyloxymethyl]-N,N- dimethyl-n-propylamine, (2S,3S-tartrate], derived from the arylacetamide series, is an opioid drug which acts as a selective agonist for kappa(1a)-opioid receptor. Pharmacological studies have shown that fedotozine exerts a peripheral antinociceptive action, comparable with that of other kappa-agonists. Results of Phase III trials of fedotozine against irritable bowel syndrome and dyspepsia have ultimately been disappointing and was lack of efficacy in subsequent studies.

Pumosetrag is a novel, orally active and selective 5-HT 3 agonist. It is a partial agonist in rats and guinea-pig and a full agonist in the mouse, suggesting important species differences in 5-HT3 receptor structure. Pumosetrag had been in phase II clinical trials for the treatment of gastroesophageal reflux disease and irritable bowel syndrome. No serious adverse events were reported. Diarrhea was not more common on the drug and only one subject experienced pruritus. All researches on this drug candidate are discontinued.