Ofloxacin is a Fluoroquinolone Antibiotic
Ofloxacin belongs to the fluoroquinolone class of antibiotics, specifically a second-generation fluoroquinolone with broad-spectrum antibacterial activity. 1
Mechanism of Action
Fluoroquinolones, including ofloxacin, exert their bactericidal activity by binding to DNA gyrase and topoisomerase IV 2. This mechanism:
- Impedes the formation of supercoiled DNA
- Inhibits the relaxation of supercoiled DNA
- Promotes double-strand DNA breakage
The drug inhibits bacterial topoisomerase IV and DNA gyrase (both type II topoisomerases), which are enzymes required for DNA replication, transcription, repair, and recombination 1.
Chemical Structure
Ofloxacin is a fluorinated carboxyquinolone with the chemical formula C₁₈H₂₀FN₃O₄ 1. It is the racemic form (±)-9-fluoro-2,3-dihydro-3-methyl-10-(4-methyl-1-piperazinyl)-7-oxo-7H-pyrido[1,2,3-de]-1,4-benzoxazine-6-carboxylic acid. The molecule contains a pyridobenzoxazine ring that decreases the extent of parent compound metabolism 1.
Classification Within Fluoroquinolones
Ofloxacin is classified as a second-generation fluoroquinolone 3. The fluoroquinolone generations are:
- First generation: Nalidixic acid (prototype quinolone)
- Second generation: Ciprofloxacin, levofloxacin, norfloxacin, and ofloxacin - characterized by greater Gram-negative spectrum including activity against Pseudomonas aeruginosa
- Third generation: Gemifloxacin - substantially increased activity against Streptococcus pneumoniae
- Fourth generation: Moxifloxacin - increased activity against anaerobes
Comparative Positioning
Within the fluoroquinolone class, ofloxacin is considered an earlier-generation agent with inferior activity compared to later-generation fluoroquinolones like levofloxacin and moxifloxacin 2, 4. Levofloxacin is actually the active L-isomer of ofloxacin and can be used in place of ofloxacin at a dose of 250 mg 5.
Important Clinical Considerations
Ofloxacin shares the class-wide adverse effects of fluoroquinolones 2:
- Achilles tendon rupture and other tendinopathies (particularly concerning in patients with renal dysfunction)
- Gastrointestinal absorption inhibited by multivalent cations (magnesium, aluminum, iron, calcium)
- Not approved for use in children in the United States (contraindicated for persons ≤17 years of age) 6
- Risk of selecting resistant pathogens, especially S. pneumoniae and Pseudomonas aeruginosa