Moxifloxacin is preferred over ciprofloxacin for community-acquired pneumonia with atypical cover because:
- A Ciprofloxacin is inactive against all atypical organisms
- B Moxifloxacin preferentially inhibits topoisomerase IV over gyrase in Gram-positive organisms and has extended-spectrum including Streptococcus pneumoniae ✓
- C Moxifloxacin has superior urinary penetration enabling dual-site coverage
- D Moxifloxacin inhibits both gyrase and topoisomerase II in mycobacteria, providing TB prophylaxis
Correct answer: B. Moxifloxacin preferentially inhibits topoisomerase IV over gyrase in Gram-positive organisms and has extended-spectrum including Streptococcus pneumoniae
Explanation
Fluoroquinolones inhibit bacterial DNA gyrase (topoisomerase II) and topoisomerase IV. In Gram-positive bacteria, the primary target is topoisomerase IV; in Gram-negatives, it is gyrase. Moxifloxacin (a 4th-generation, C8-methoxy fluoroquinolone) has enhanced Gram-positive activity due to the methoxy group at C8, covering S. pneumoniae, S. aureus, and atypicals (Mycoplasma, Legionella, Chlamydia). Ciprofloxacin has poor S. pneumoniae coverage. Moxifloxacin has poor urinary excretion — it is NOT used for UTIs.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.