A 65-year-old diabetic patient with chronic osteomyelitis due to methicillin-resistant Staphylococcus aureus (MRSA) is started on linezolid. Which of the following is a unique characteristic of linezolid's mechanism of action?
- A It inhibits the 30S ribosomal subunit, preventing aminoacyl-tRNA binding
- B It inhibits the 50S ribosomal subunit by preventing peptidyl transferase activity
- C It prevents formation of the 70S initiation complex by binding the 23S rRNA of the 50S subunit ✓
- D It inhibits RNA polymerase sigma factor, blocking transcription initiation
Correct answer: C. It prevents formation of the 70S initiation complex by binding the 23S rRNA of the 50S subunit
Explanation
Linezolid, an oxazolidinone, has a unique mechanism among antibiotics: it binds the 23S rRNA of the 50S ribosomal subunit at a site that prevents the assembly of the 30S-50S 70S initiation complex. This early blockade of translation initiation is structurally distinct from other 50S inhibitors like macrolides, chloramphenicol, or lincosamides. Because of its novel binding site, there is no cross-resistance with other ribosomal inhibitors, making it valuable for multidrug-resistant organisms.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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