Ciprofloxacin vs Levofloxacin

## Overview

Ciprofloxacin and levofloxacin are both fluoroquinolone antibiotics that inhibit bacterial topoisomerases, but they differ importantly in their antimicrobial spectrum, particularly regarding respiratory pathogens. Levofloxacin is a respiratory fluoroquinolone with activity against Streptococcus pneumoniae; ciprofloxacin has superior gram-negative and Pseudomonas coverage.

## Mechanism of Action

Both inhibit bacterial DNA gyrase (topoisomerase II) and topoisomerase IV, preventing DNA supercoiling relief and DNA replication. They are concentration-dependent antibiotics (efficacy correlates with Cmax/MIC ratio), making higher single doses sometimes more effective than multiple small doses.

## Antimicrobial Spectrum

Ciprofloxacin: exceptional activity against gram-negative organisms, Enterobacteriaceae, Pseudomonas aeruginosa (most potent fluoroquinolone vs. Pseudomonas), and atypical pathogens. Weaker activity against S. pneumoniae — inadequate for community-acquired pneumonia (CAP) monotherapy.

Levofloxacin: broader gram-positive coverage (excellent S. pneumoniae activity), good Pseudomonas activity (though less than ciprofloxacin), and atypicals. FDA-approved for CAP (including drug-resistant S. pneumoniae), HAP, and UTI.

## Pharmacokinetics

Ciprofloxacin: oral bioavailability ~70–80%, half-life 4–6 h, primarily renal excretion. Levofloxacin: oral bioavailability ~99%, half-life 6–8 h, once-daily dosing possible. Both have excellent tissue penetration and intracellular accumulation.

## Key Indications

Ciprofloxacin: UTI (especially complicated), prostatitis, intra-abdominal infections (with metronidazole), typhoid, infectious diarrhea, anthrax prophylaxis, Pseudomonas infections. Levofloxacin: CAP (including DRSP), HCAP, acute bacterial exacerbation of COPD, sinusitis.

## QTc Warning

Both prolong QTc interval; levofloxacin more so than ciprofloxacin. Moxifloxacin prolongs QTc most. Avoid all fluoroquinolones in patients with baseline QTc prolongation.

## Key Takeaways

- Ciprofloxacin: best Pseudomonas coverage; inferior S. pneumoniae (not for CAP monotherapy)
- Levofloxacin: respiratory fluoroquinolone; excellent for CAP; good Pseudomonas
- Both excellent tissue penetration; once-daily levofloxacin preferred by some for adherence