Lincosamides and Amphenicols
Lincosamides and Amphenicols are antibiotics that inhibit bacterial protein synthesis by acting on the 50S ribosomal subunit. While lincosamides are mostly used for Gram-positive and anaerobic infections, amphenicols have broader utility but are reserved for serious infections due to potential toxicity.
Classification / Examples
- Lincosamides: Clindamycin, Lincomycin
- Amphenicols: Chloramphenicol, Thiamphenicol
Pharmacodynamics
- Lincosamides:
- Bind to the 50S ribosomal subunit near the peptidyl transferase center.
- Inhibit peptide bond formation, halting elongation of the peptide chain.
- Bacteriostatic in action.
- Active against:
- Gram-positive cocci: Staphylococcus aureus (some MRSA), Streptococcus pneumoniae
- Anaerobes: Bacteroides fragilis
- Ineffective against most Gram-negative bacteria due to poor outer membrane penetration.
- Amphenicols:
- Also bind to the 50S ribosomal subunit and inhibit peptidyl transferase.
- Broad-spectrum, effective against Gram-positive, Gram-negative, anaerobes, rickettsiae, and some atypicals.
- Chloramphenicol is especially useful for CNS infections due to excellent CSF penetration.
- Bacteriostatic, but can be bactericidal in certain infections (e.g. meningitis).
Side Effects
- Lincosamides:
- GI disturbances: nausea, vomiting, diarrhea
- Clostridioides difficile colitis (black box warning)
- Rashes, urticaria, anaphylaxis (rare)
- Potential neuromuscular blockade if used with muscle relaxants
- Amphenicols:
- GI effects: nausea, vomiting, diarrhea
- Aplastic anemia (idiosyncratic, irreversible, rare but fatal)
- Bone marrow suppression (dose-dependent and reversible)
- Gray baby syndrome in neonates (due to immature glucuronidation)
- Headache, confusion, optic neuritis (rare)