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Tetracycline and Chloramphenicol: Broad-Spectrum Antibiotics
Tetracyclines
Mechanism of Action
Tetracyclines inhibit bacterial protein synthesis by binding to the 30S ribosomal subunit, preventing the attachment of aminoacyl-tRNA to the ribosome.
Mechanism of Resistance
- Efflux pumps actively transport tetracycline out of the bacterial cell.
- Ribosomal protection proteins displace tetracycline from the ribosome.
- Enzymatic inactivation through bacterial enzymes degrading tetracycline.
Therapeutic Uses
- Respiratory infections (e.g., pneumonia, Mycoplasma pneumoniae, Chlamydia pneumoniae).
- Acne vulgaris.
- Urinary tract infections.
- Rickettsial infections (e.g., Rocky Mountain spotted fever).
- Lyme disease and cholera.
Adverse Effects
- Gastrointestinal disturbances: Nausea, vomiting, diarrhea.
- Dental discoloration in children under 8 years.
- Photosensitivity and liver toxicity.
- Rare nephrotoxicity in patients with preexisting kidney disease.
Contraindications
- Pregnancy (category D) due to risks of fetal bone growth inhibition.
- Children under 8 years of age due to tooth discoloration.
Chloramphenicol
Mechanism of Action
Chloramphenicol inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit and preventing peptide bond formation.
Mechanism of Resistance
- Acetylation by chloramphenicol acetyltransferase (CAT) inactivates the drug.
- Alteration of the ribosomal binding site decreases drug binding efficiency.
Therapeutic Uses
- Serious infections like meningitis and typhoid fever.
- Rickettsial infections, especially when tetracyclines are contraindicated.
- Topical use for eye infections.
Adverse Effects
- Bone marrow suppression, including aplastic anemia.
- Gray baby syndrome in neonates due to immature liver metabolism.
- Gastrointestinal issues: Nausea, vomiting, and diarrhea.
- Hypersensitivity reactions such as rash and anaphylaxis.
Contraindications
- Neonates due to the risk of gray baby syndrome.
- Pregnancy: Only when necessary, as it crosses the placenta and can affect fetal bone marrow.
- Preexisting bone marrow disorders.
