This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Systemic Bacteriology (Gram Positive Bacilli, Gram Negative Bacilli), Subject name: Microbiology
Which is the drug to treat NARST (Nalidixic acid resistant S.typhi)? 
Select and explain. 
A. Chloramphenicol, B. Azithromycin, C. Ciprofloxacin, D. Septran
B: Azithromycin
Answer: B: Azithromycin 
Explanation: Nalidixic acid-resistance S.typhi (NARST): Surrogate marker of decreased susceptibility to ciprofloxacin. Rx : Azithromycin , third-generation cephalosporins. Aztreonam and Imipenem are the potential second line drugs.