Examples of Tetracycline Antibiotics
The main tetracycline antibiotics include tetracycline, doxycycline, minocycline, and newer generation tetracyclines such as tigecycline, omadacycline, eravacycline, and sarecycline. 1, 2, 3
First and Second Generation Tetracyclines
- Tetracycline - The original tetracycline antibiotic that gives the class its name 1
- Doxycycline - A second-generation tetracycline with improved absorption and longer half-life (18-22 hours) compared to tetracycline 2, 4
- Minocycline - A second-generation tetracycline with better tissue penetration and lipid solubility 4, 5
Third Generation Tetracyclines
- Tigecycline - A glycylcycline derivative effective against many resistant bacteria 3
- Omadacycline - An aminomethylcycline with activity against resistant organisms 3
- Eravacycline - A fluorocycline with broad-spectrum activity 3
- Sarecycline - A narrow-spectrum tetracycline specifically developed for acne treatment 3
Mechanism of Action
Tetracyclines work primarily by:
- Inhibiting bacterial protein synthesis by binding to the 30S ribosomal subunit 2
- Preventing aminoacyl-tRNA molecules from binding to the ribosomal acceptor sites 6
- Exhibiting both bacteriostatic and anti-inflammatory properties 5
Clinical Applications
Tetracyclines are used to treat various conditions including:
- Respiratory infections caused by susceptible strains of Streptococcus pneumoniae, Haemophilus influenzae, and Mycoplasma pneumoniae 1, 2
- Skin and soft tissue infections 1, 5
- Acne vulgaris (particularly doxycycline, minocycline, and sarecycline) 5, 3
- Meibomian gland dysfunction and blepharitis 5
- Chlamydial infections and sexually transmitted diseases 1, 7
- Rickettsial infections including Rocky Mountain spotted fever 1
- Lyme disease (borreliosis) 4
Important Considerations and Contraindications
- Contraindicated in pregnancy and children under 8 years of age due to risk of teeth staining and bone development issues 5
- Can cause photosensitization and increased risk of sunburn 5, 6
- May cause gastrointestinal upset, vaginitis, and rarely azotemia 5, 7
- Minocycline has been reported to stain skin, nails, sclera, teeth, conjunctiva, tongue, and bone 5
- Tetracyclines have been implicated in cases of pseudotumor cerebri 5, 6
- May alter the effectiveness of certain medications (e.g., decrease oral contraceptive effectiveness and potentiate warfarin effects) 5
- Doxycycline has been associated with esophageal irritation and potential perforation if not taken with adequate fluid 6
Alternatives in Special Populations
- For women of childbearing age and children where tetracyclines are contraindicated, macrolides such as erythromycin or azithromycin may be used as alternatives 5
- For children with blepharitis, a suggested dosing regimen for erythromycin is 30-40 mg/kg divided over 3 doses for 3 weeks, then twice daily for 4-6 weeks 5
- Azithromycin at 5 mg/kg daily for 2 months has shown clinical improvement in children with blepharitis 5
Resistance Concerns
- Bacterial resistance to tetracyclines is increasing due to their extensive use in human and animal medicine 8
- Resistance mechanisms include efflux pumps that remove the drug from bacterial cells and ribosomal protection proteins 8
- Newer generation tetracyclines were developed to overcome some resistance mechanisms 3
Tetracyclines remain valuable antibiotics due to their broad spectrum of activity, but their use should be judicious to minimize further development of resistance 8.