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Macrolides: Mechanism, Uses, and Adverse Effects
Introduction to Macrolides
Macrolides are a class of antibiotics known for their large lactone ring structure and their ability to inhibit bacterial protein synthesis. These antibiotics are commonly used to treat respiratory infections, skin infections, and certain sexually transmitted diseases.
Examples of Macrolides
- Erythromycin
- Azithromycin
- Clarithromycin
- Roxithromycin
- Telithromycin
Mechanism of Action
Macrolides bind to the 50S ribosomal subunit and inhibit protein synthesis by blocking the translocation step. This results in bacteriostatic effects, though they can be bactericidal in high concentrations.
Mechanism of Resistance
- Modification of Target Site: Methylase enzymes modify the 23S rRNA of the ribosomal subunit, preventing macrolides from binding.
- Efflux Pumps: Bacteria may use efflux pumps to expel macrolides, reducing intracellular concentrations.
- Enzymatic Inactivation: Some bacteria produce enzymes that break down macrolides, rendering them ineffective.
Therapeutic Uses
- Respiratory tract infections (e.g., pneumonia, bronchitis)
- Skin and soft tissue infections
- Sexually transmitted diseases (e.g., chlamydia, gonorrhea)
- Helicobacter pylori eradication
- Streptococcal infections (in penicillin-allergic patients)
Adverse Effects
- Gastrointestinal disturbances (nausea, vomiting, diarrhea)
- QT interval prolongation (increased risk of arrhythmias)
- Hepatotoxicity (especially with erythromycin)
- Allergic reactions (rash, eosinophilia, anaphylaxis)
- Reversible hearing loss (especially with erythromycin)
Contraindications
- Hypersensitivity to macrolides
- Severe liver disease
- Cardiac arrhythmias (due to QT prolongation)
- Drug interactions (e.g., with warfarin, digoxin, and statins)
