This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Antibiotics, Subject name: Pharmacology
[{'content': 'Select the antimicrobial drug which is used orally only for urinary tract infection or for bacterial diarrhoeas \nSelect and explain. \nA. Bacampicillin, B. Nalidixic acid, C. Azithromycin, D. Pefloxacin', 'role': 'user'}, {'content': 'Answer: B \nExplanation: QUINOLONES Nalidixic acid It is active against gram-negative bacteria, especially coliforms: E. coli, Proteus, Klebsiella, Enterobacter, Shigella but not Pseudomonas. mech of action:- It acts by inhibiting bacterial DNA gyrase and is bactericidal. Use s:- 1. Nalidixic acid is primarily used as a urinary antiseptic. 2. It has also been employed in diarrhoea caused by Proteus, E. coli, Shigella or Salmonella, but norfloxacin/ciproloxacin are more commonly used now. Ref:- kd tripathi; pg num:-709', 'role': 'assistant'}]