Which of the following drugs is used for Irritable Bowel Syndrome of the constipating type:

Answer is A (Lubiprostone) Lubiprostone is an effective agent for treatment of patient with constipation predominant Irritable Bowel Syndrome. Lubiprostone is a novel chloride channel activator that stimulates chloride channels in the apical membrane of intestinal epethelial cells. Chloride secretion induces passive movement of sodium and water into the bowel lumen and improves constipation predominant IBS. Cholestyramine and Alosetron are used for the management of patients with Diarrhea predominant Irritable Bowel Syndrome. Rifaximin is a non-absorbed oral antibiotic being evaluated for global Irritable Bowel Syndrome Symptoms. It is not .specific fior constipation predominant IBS and currently there is still insufficienct data to recommend routine use of this antibiotic in the treatment of IBS.