Levofloxacin vs Norfloxacin

## Overview

Levofloxacin is a third-generation respiratory fluoroquinolone with excellent systemic distribution and S. pneumoniae coverage. Norfloxacin is a second-generation agent with poor systemic penetration limited to urinary tract use. This represents a significant generational gap in fluoroquinolone development.

## Mechanism of Action

Both inhibit DNA gyrase and topoisomerase IV. Levofloxacin's structural modifications confer greater gram-positive activity and systemic bioavailability.

## Pharmacokinetics

Levofloxacin: ~99% oral bioavailability, 6–8 h half-life, renal elimination, once-daily dosing. Norfloxacin: 30–40% bioavailability, 3–4 h half-life, urinary focus. Levofloxacin achieves excellent tissue levels; norfloxacin does not.

## Spectrum

Levofloxacin covers the full gram-negative spectrum plus excellent S. pneumoniae and atypicals. Norfloxacin is limited to gram-negative uropathogens.

## Key Takeaways

- Levofloxacin: comprehensive systemic fluoroquinolone; full spectrum
- Norfloxacin: UTI-only; obsolete in most modern formularies
- No scenario where norfloxacin is preferred over levofloxacin for any indication