Which antibiotic class predominantly inhibits bacterial protein synthesis at the 30S ribosomal subunit and is known for potential ototoxicity and nephrotoxicity?

• A. Macrolides.
• B. Tetracyclines.
• C. Beta-lactams.
• D. Aminoglycosides (e.g., gentamicin).

Answer: (D)

Aminoglycosides work by binding irreversibly to the 30S ribosomal subunit, which misreads the mRNA and prevents proper initiation of protein synthesis. This leads to a rapid, bactericidal effect and requires the drug to enter the bacterial cell, a process helped by oxygen-dependent uptake. They are well known for two major toxicities: ototoxicity, which can affect hearing or balance, and nephrotoxicity, which damages kidney tubule cells—risks that increase with higher doses or longer courses, in people with kidney impairment, or when combined with other nephrotoxins. Because of this mechanism and these toxicity risks, this class is the one described. Macrolides target the 50S subunit and don’t share this toxicity pattern, beta-lactams inhibit cell wall synthesis, and tetracyclines also hit the 30S but are more associated with photosensitivity and dental effects rather than predominant ototoxic/nephrotoxic toxicity.