This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
A patient is taking 40 mg Famotidine OD, Sucralfate and Antacid tablets TDS, This treatment is irrational because of - 
Select and explain. 
A. Sucralfate decreases the absorption of famotidine, B. Sucralfate increases the toxicity of famotidine, C. Suralfate decreases absorption of antacids, D. Suralfacte polymerises only when gastric pH is less than 4
D: Suralfacte polymerises only when gastric pH is less than 4
Answer: D: Suralfacte polymerises only when gastric pH is less than 4 
Explanation: Ans. is 'd' i.e., Sucralfate polymerizes only when gastric pH is <4 Sucralfate is an ulcer protective agent. It preferentially and strongly adheres to the ulcer base, specially duodenal, and acts as a physical barrier preventing acid, pepsin and bile from coming in contact with the ulcer base. However, this protective action is attributed to sucralfate because of ceain propeies which are achieved only in acidic medium : a) Acidic medium gives it a viscous consistency, also b) It polymerises at pH <4 by cross linkages of molecule assuming sticky gel like consistency. It is this viscous and gel like propeies that are responsible for its action. When antacids are given concurrently they raise the pH of gastric secretion and this interferes with the very basic mechanism of action of sucralfate (requires pH <4) and thus makes them ineffective.