This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gastrointestinal tract, Subject name: Pharmacology
Linaclotide is used for the following indication? 
Select and explain. 
A. IBS-Diarrhea dominant, B. IBS-constipation dominant, C. Ulcerative colitis, D. Non-specific diarrhea
B: IBS-constipation dominant
Answer: B: IBS-constipation dominant 
Explanation: Linaclotide-chloride channel activator: 290mg OD approved by FDA for constipation in Irritable bowel syndrome.Linaclotide is a poorly absorbed 14-amino-acid peptide that binds to the guanylate cyclase C receptor on the luminal surface of intestinal enterocytes, activating the cystic fibrosis transmembrane conductance channel and stimulating intestinal fluid secretion. Preliminary results of phase 3 clinical trials confirm its efficacy in patients with chronic constipation.Ref: Katzung 13th ed. Pg 1068