Aminoglycosides
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Antibiotics / Antiparasitics
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Summary
Aminoglycosides are a class of antibiotics that includes the drugs gentamicin, amikacin, streptomycin, and neomycin. These antibiotics work by binding to the 30S ribosomal subunit of bacteria to prevent bacterial protein synthesis. Aminoglycosides are notable for only treating aerobic organisms, since oxygen is required for drug uptake. Adverse effects of aminoglycoside antibiotics include ototoxicity, nephrotoxicity, and neuromuscular blockade or paralysis. Aminoglycosides are also teratogenic and should not be used during pregnancy. Finally, chemical modifications or attachments of chemical groups to the drug by bacterial enzymes are the main mechanism of antibiotic resistance.
Key Points
- Aminoglycosides
- Drug Names
- Gentamicin
- Amikacin
- Neomycin
- Streptomycin
- Tobramycin
- Mechanism
- Irreversible binding to 30S subunit of bacterial ribosomes
- Inhibits formation of initiation complex, translocation, and causes misreading of mRNA
- Prevents bacterial protein synthesis
- Synergistic effect with beta-lactam antibiotics
- Penicillins inhibit bacterial cell wall synthesis, which enable entry of aminoglycosides into interior of bacterial cells
- Bactericidal
- Irreversible binding to 30S subunit of bacterial ribosomes
- Clinical Use
- Requires O2 for uptake
- Treats aerobic organisms only
- Severe gram-negative rod infections
- Bowel surgery infection prophylaxis (neomycin)
- Streptomycin: Mycobacterium tuberculosis (2nd-line)
- Requires O2 for uptake
- Adverse Effects
- Nephrotoxicity
- Can cause tubular necrosis
- Ototoxicity
- Presents with hearing loss and tinnitus
- Risk compounded with loop diuretics (also cause ototoxicity)
- Damage to CN VIII can also lead to vestibular ataxia and vertigo
- Neuromuscular blockade
- Seen with large doses or intrapleural administration
- Contraindicated in patients with myasthenia gravis
- Teratogenicity
- Nephrotoxicity
- Resistance
- Enzyme modification of drug
- Bacterial transferase enzymes inactivate the drug by acetylation, phosphorylation, or adenylation
- Attachment of these groups reduces access to ribosomes
- Most of these enzymes are plasmid-encoded
- Seen with Enterococcus
- Enzyme modification of drug
- Drug Names