Notes on Aminoglycoside Pharmacology, Mechanism, ADR, Uses and MCQ for GPAT, NEETPG
Mechanism of Action:
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Aminoglycosides irreversibly bind to the 30S ribosomal subunit of bacteria.
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This inhibits initiation of protein synthesis, causes misreading of mRNA, and leads to abnormal/nonfunctional proteins.
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Bactericidal in action (unusual for protein synthesis inhibitors).
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Oxygen-dependent active transport into bacterial cells—ineffective against anaerobes.
Pharmacokinetics:
| Property | Details |
|---|---|
| Absorption | Poor oral absorption → given parenterally (IV/IM) for systemic use |
| Distribution | Extracellular fluid; poor CNS and eye penetration; accumulates in renal cortex and inner ear |
| Metabolism | Not metabolized significantly |
| Excretion | Renal (unchanged); dose adjustment needed in renal impairment |
| Half-life | 2–3 hours (increased in renal dysfunction) |
Clinical Uses:
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Severe aerobic Gram-negative infections (e.g., Pseudomonas, E. coli, Klebsiella)
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Tuberculosis (e.g., streptomycin)
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Synergistic use with β-lactams or vancomycin for enterococcal endocarditis
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Bowel sterilization (oral neomycin pre-surgery)
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Topical use for skin, eye, and ear infections
Contraindications:
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Pregnancy (risk of fetal ototoxicity)
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Myasthenia gravis (exacerbates neuromuscular blockade)
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Pre-existing renal or auditory dysfunction
Adverse Drug Reactions (ADRs):
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Nephrotoxicity – reversible, dose-dependent (monitor serum creatinine)
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Ototoxicity – irreversible, affects cochlear and/or vestibular systems
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Neuromuscular blockade – can cause respiratory paralysis, especially with anesthesia or muscle relaxants
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Teratogenicity – especially ototoxic to fetus (category D)
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Allergic reactions – rare
Common Aminoglycosides:
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Gentamicin
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Amikacin
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Tobramycin
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Streptomycin
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Neomycin (mostly topical/oral use)
MCQs on Aminoglycosides
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What is the primary mechanism of action of aminoglycosides?
A. Inhibits DNA synthesis
B. Binds 30S ribosomal subunit
C. Inhibits peptidoglycan synthesis
D. Binds 50S ribosomal subunit
Answer: B. Binds 30S ribosomal subunit -
Which adverse effect is most commonly associated with aminoglycosides?
A. Hepatotoxicity
B. Nephrotoxicity
C. Photosensitivity
D. Agranulocytosis
Answer: B. Nephrotoxicity -
Aminoglycosides are ineffective against anaerobes because:
A. They are broken down by anaerobes
B. They cannot enter cells without oxygen-dependent transport
C. Anaerobes lack 30S subunits
D. They are effluxed rapidly
Answer: B. They cannot enter cells without oxygen-dependent transport -
Which of the following aminoglycosides is mainly used orally for bowel sterilization?
A. Gentamicin
B. Amikacin
C. Neomycin
D. Tobramycin
Answer: C. Neomycin -
Which condition is a contraindication for aminoglycoside use?
A. Bacterial meningitis
B. Pregnancy
C. Asthma
D. Type 2 diabetes
Answer: B. Pregnancy
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