Fluoroquinolones
One-Sentence Definition
Fluoroquinolones inhibit bacterial DNA gyrase and topoisomerase IV, providing broad Gram-negative (and some Gram-positive) activity — with chromosomal resistance common and significant toxicity/t stewardship concerns.
Simple Explanation
They block DNA replication enzymes — good for many urinary and respiratory Gram-negatives when susceptible, but resistance rises fast.
Detailed Scientific Explanation
| Agent (examples) | Notes |
|---|---|
| Ciprofloxacin | Pseudomonas-capable (context); GI/UTI |
| Levofloxacin | Respiratory Gram-positives/negatives (when susceptible) |
| Moxifloxacin | Anaerobic/atypical coverage nuances |
Spectrum: Enterobacterales, Pseudomonas (cipro), atypicals (Legionella, Mycoplasma) — always check local AST.
Resistance: gyrA/parC mutations; plasmid-mediated qnr (low-level); efflux — often multi-step.
Toxicities: tendon rupture, QT prolongation, CNS effects, glucose dysregulation — affects empiric use.
Mechanism
Trap gyrase/topoisomerase on DNA → double-strand breaks → bactericidal effect (concentration-dependent).
Clinical Importance
- Uncomplicated cystitis options where susceptibility known
- Not reliable empiric therapy for Gonorrhea (widespread resistance)
- TB (ofloxacin/moxifloxacin) in MDR regimens — specialized use
AMR Relevance
- Selects rapidly in E. coli UTIs and Campylobacter (One Health)
- Part of MDR/XDR Typhoid and Enterobacterales profiles
Related MOCs
Active Recall Questions
- Primary enzymatic targets?
- Why avoid FQ for gonorrhea empirically?
- Concentration-dependent killing — dosing implication?