A 45-year-old man with H. pylori-positive duodenal ulcer is started on standard triple therapy with clarithromycin, amoxicillin, and omeprazole. Clarithromycin is the key macrolide in this regimen. The mechanism by which clarithromycin inhibits protein synthesis is:
- A Binding to the 30S ribosomal subunit and blocking initiation complex formation
- B Inhibiting peptidyl transferase activity at the 50S subunit
- C Binding to the 50S ribosomal subunit and blocking translocation ✓
- D Blocking aminoacyl-tRNA entry at the 30S A site
Correct answer: C. Binding to the 50S ribosomal subunit and blocking translocation
Explanation
Macrolides bind to the 23S rRNA of the 50S ribosomal subunit and block translocation of the peptidyl-tRNA from A site to P site. Option A describes aminoglycoside mechanism. Option B describes chloramphenicol mechanism. Option D describes tetracycline mechanism. Knowing these distinct ribosomal sites is essential for pharmacology exams.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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