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
Drug used in irritable bowel syndrome with constipation is? 
Select and explain. 
A. Lubiprostone, B. Loperamide, C. Alosetrone, D. Clonidine
A: Lubiprostone
Answer: A: Lubiprostone 
Explanation: Lubiprostone acts by stimulating cl- channel opening in the intestine increasing liquid secretion in the gut and decresing transit time therefore used for chronic constipation. It has also been approved for constipation dominant irritable bowel syndrome in women.( ref katzung 11/e p1080)