Select the antimicrobial drug which is used orally only for urinary tract infection or for bacterial diarrhoeas

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