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Antibiotic Mechanisms — MFDS Part 1 MCQ

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ModeratePharmacologyAntibiotic MechanismsMFDS Part 1

Which of the following antibiotics inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit?

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Correct answer: B — Erythromycin

Erythromycin is the correct answer. It is a macrolide that binds to the bacterial 50S ribosomal subunit and suppresses protein synthesis. The other agents act through distinct targets: amoxicillin binds penicillin-binding proteins and inhibits bacterial cell-wall synthesis; metronidazole forms reactive intermediates that damage DNA in susceptible anaerobic organisms; ciprofloxacin inhibits bacterial DNA gyrase and topoisomerase IV; and trimethoprim inhibits bacterial dihydrofolate reductase, disrupting folate metabolism. Thus, erythromycin is the only listed antibiotic whose principal antibacterial mechanism involves the 50S ribosomal subunit.

Reference: electronic Medicines Compendium (emc), Erythromycin Lactobionate 1g Powder for Solution for Infusion, Summary of Product Characteristics, section 5.1 Pharmacodynamic properties, revised 15 May 2024. https://www.medicines.org.uk/emc/product/405/smpc