Antibiotics - Inhibitors Of Protein Synthesis

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Bactericidal inhibitors

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1. Aminoglycosides
2. Streptogramins

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Aminoglycosides (Names)

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1. Gentamicin
2. Amikacin
3. Tobramycin
4. Streptomycin

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Streptogramins (Names)

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1. Dalfopristin
2. Quinupristin

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Aminoglycosides:
Administration & Distribution

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Parenteral administration
Poor GI absorption
No CSF distribution
Concentration-dependent killing
Long post-antibiotic effect

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Aminoglycosides:
Elimination

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Renal excretion
Unchanged form

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Aminoglycosides:
Toxic effects

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Ototoxicty; nephrotoxicity; neuromuscular blockade (possible)

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Aminoglycosides:
Mechanism of action

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Oxygen dependent uptake across cytoplasmic membrane (only aerobes affected)
Binds to 30S subunit & breaks down initiation complex

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Aminoglycosides:
Antimicrobial activity

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Gram-negative aerobes
Combined w/ B lactam for gram-positive bacilli (synergistic relationship)

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Aminoglycosides:
Resistance mechanisms

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1) Enzymes which phosphorylate, adenylate or acetylate
2) Decreased uptake
3) Alteration of 30S binding site

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Spectinomycin:
Administration

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Parenteral (IM)

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Spectinomycin:
Elimination

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Excreted by kidneys in original form

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Spectinomycin:
Toxicity

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Nausea, chills, fever, dizziness, rashes

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Spectinomycin:
Mechanism of action

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Bacteriostatic;
Binds to 30S & 70S subunits to bind translocation step of synthesis

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Spectinomycin:
Antimicrobial activity

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Alternative to penicillin-allergic patients for treatment of fluoroquinolone-resistant Neisseria gonorrhoeae

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Bacteriostatic inhibitors

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1. Spectinomycin
2. Chloramphenicol
3. Tetracyclines
4. Erythromycin
5. Clindamycin
6. Linezolid (Oxazolidinones)

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Chloramphenicol:
Administration & distribution

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Absorbed from the GI tract & enters CNS

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Chloramphenicol:
Elimination

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Inactivated in liver by glucuronyl transferase

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Chloramphenicol:
Toxic effects

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Aplastic anemia rare but fatal
Dose-related bone marrow toxicity
Gray-baby syndrome
Inhibits P450 metabolism

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Chloramphenicol:
Mechanism of action

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Bacteriostatic
Binds to 50S subunit of 70S ribosome & inhibits peptidyl transferase

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Chloramphenicol:
Mechanism of resistance

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Enzyme, chloramphenicol acetyl transferase (CAT) acetylates & inactivates the drug.
Plasmid-mediated

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Tetracyclines (Names)

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1. Doxycycline
2. Minocycline
Bacteriostatic

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Tetracyclines:
Administration and distribution

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PO or IV
Impaired by milk, cations, iron preparations b/c of chelation of these ions by the drug & poor absorption
No entry into CNS

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Tetracyclines:
Elimination

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Removed by liver & enters enterohepatic circulation
Eliminated by feces & urine

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Tetracyclines:
Toxic effects

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GI irritation
Photosensitivity (doxycycline)
Hepatotoxicity w/ overdosing
Bone deposition (discoloration)
Outdated cause Fanconi syndrome
Potentially nephrotoxic if renal insufficiency

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Tetracyclines:
Mechanism of action

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Bacteriostatic
Bind to 30S subunit of 70S ribosome & inhibit binding of amino acyl-tRNA

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Tetracyclines:
Antimicrobial activity

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Mycoplasma pneumoniae, rickettsial infections, Chlamydiae, Vibrio cholera, Brucella, Borrelia

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Tetracyclines:
Mechanisms of resistance

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1) Increased efflux by active transport pump
2) Ribosome protection from proteins which interfere with binding

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Clindamycin:
Administration and distribution

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PO or parenteral
No CSF entry

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Clindamycin:
Elimination

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10% excreted in kidney
Metabolized in liver & excreted in bile
Long excretion time (2 weeks)

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Clindamycin:
Toxic effects

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Severe diarrhea (pseudomembranous colitis) due to C. difficile
Hepatotoxicity

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Clindamycin:
Mechanism of action

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Bacteriostatic
Binds 50S subunit of 70S ribosome & blocks the binding of the aminoacyl-tRNA substrate to the A site on the ribosome

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Clindamycin:
Antimicrobial activity

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Moderate to severe anaerobic infections

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Clindamycin:
Mechanism of resistance

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1) Mutation of the ribosomal binding site
2) Production of methylase
3) Inactivation of the drug