Which antibacterial drug class is not used primarily to inhibit protein synthesis?

• A. Aminoglycosides
• B. Streptogramins
• C. Oxazolidinones
• D. Fluoroquinolones

Answer: (D)

Understanding how antibiotics act helps here. Drugs that inhibit protein synthesis do so by targeting the bacterial ribosome and blocking steps of translation. Aminoglycosides bind the 30S subunit and cause misreading of mRNA, stopping initiation and producing faulty proteins. Streptogramins interfere with the 50S subunit to halt elongation of the polypeptide chain. Oxazolidinones prevent formation of the initiation complex on the 50S subunit, stopping translation from starting.

Fluoroquinolones, by contrast, do not affect protein synthesis. They target enzymes essential for DNA replication—DNA gyrase and topoisomerase IV—so they block DNA replication and bacterial growth rather than translation.

Therefore, the class that is not used primarily to inhibit protein synthesis is the one that disrupts DNA replication.