Paper II
Question
Enumerate macrolide antibiotics. Describe briefly its mechanism of action and mention four uses. Add a note on linezolid. (1+2+1+2=6)
Answer
Macrolide antibiotics
- Erythromycin
- Azithromycin
- Clarithromycin
- Roxithromycin
Mechanism of action
- Bind reversibly to the 50S ribosomal subunit of bacteria
- Inhibit bacterial protein synthesis by blocking translocation (movement of the ribosome along mRNA)
- Bacteriostatic at usual doses (bactericidal at high concentrations against highly susceptible organisms)
Uses
- Atypical pneumonia (Mycoplasma, Legionella, Chlamydia)
- Alternative to penicillin in penicillin-allergic patients (streptococcal pharyngitis, syphilis)
- Whooping cough (pertussis)
- Diphtheria (carrier state and treatment, along with antitoxin)
- Chlamydial genital infections, community-acquired respiratory tract infections
Note on Linezolid
- An oxazolidinone antibiotic (not a macrolide) with a distinct mechanism — binds the 23S rRNA of the 50S subunit, preventing formation of the initiation complex for protein synthesis
- Active against Gram-positive organisms including MRSA and VRE (vancomycin-resistant enterococci)
- Reserved for multidrug-resistant Gram-positive infections
- Adverse effects: thrombocytopenia/myelosuppression with prolonged use, peripheral/optic neuropathy, serotonin syndrome (weak MAO inhibitor — caution with SSRIs)