Tetracyclines
Tetracyclines are a class of broad-spectrum antibiotics that inhibit bacterial protein synthesis. They are derived from Streptomyces species and are effective against a wide range of Gram-positive and Gram-negative bacteria.
Classification
- Natural: Oxytetracycline
- Semisynthetic: Tetracycline, Doxycycline, Minocycline
- Glycylcyclines: Tigecycline (a derivative designed to overcome resistance)
Pharmacodynamics
Tetracyclines are bacteriostatic antibiotics that inhibit bacterial protein synthesis by binding reversibly to the 30S subunit of the bacterial ribosome. This binding interferes with the attachment of aminoacyl-tRNA to the mRNA-ribosome complex, thereby preventing the addition of new amino acids to the growing peptide chain. This halts protein synthesis and inhibits bacterial growth.
They exhibit a broad spectrum of activity, including:
- Gram-positive and Gram-negative bacteria
- Spirochetes (e.g., Treponema pallidum, Borrelia burgdorferi)
- Atypical organisms (e.g., Chlamydia, Mycoplasma, Rickettsia)
- Protozoa (e.g., Entamoeba histolytica in intestinal amoebiasis)
Mechanism of Resistance
- Efflux pumps that reduce intracellular drug accumulation
- Ribosomal protection proteins that displace tetracycline from its binding site
- Enzymatic inactivation (less common)
Side Effects
- Common:
- GI upset (nausea, vomiting, diarrhea, abdominal pain)
- Photosensitivity (sunburns with light exposure) cha
- Tooth discoloration and inhibition of bone growth in children
- Rare/Serious:
- Hepatotoxicity
- Pancreatitis
- Intracranial hypertension (headache, vision changes)
- Hypersensitivity reactions (rash, anaphylaxis)
- Superinfections (C. difficile, candidiasis)