Pharmacology – MCQ 130 – Antibiotic combinations

A post operative patient developed septicemia and was empirically started on combination chemotherapy by a new resident doctor. However, when the patient did not respond even after 10 days of antibiotics treatment, the review of the charts was done. It was found that the resident doctor had started the combination of antibiotics which was mutually antagonistic in action. Which one of the following is the most likely
combination that was given?
A. Vancomycin and Amikacin
B. Cephalexin and Gentamicin
C. Ampicillin and Chloramphenicol
D. Ciprofloxacin and Piperacillin

Correct answer : C. Ampicillin and Chloramphenicol

When a Bactericidal agent is given along with a Bacteriostatic agent, 2 outcomes are possible.

  1. Synergism – when the bacteria has low sensitivity to the cidal agent
  2. Antagonism – when the bacteria has high sensitivity to the cidal agent

Bactericidal drugs:

  • Beta-lactam antibiotics (penicillin derivatives (penams), cephalosporins (cephems), monobactams, and carbapenems)
  • Vancomycin
  • Daptomycin
  • Fluoroquinolones
  • Metronidazole
  • Nitrofurantoin
  • Co-trimoxazole
  • Telithromycin
  • Aminoglycosides

Bacteriostatic drugs:

  • Tetracyclines
  • sulfonamides
  • Spectinomycin
  • Trimethoprim
  • Chloramphenicol
  • Macrolides
  • Lincosamides
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