Ciprofloxacin Classification
Ciprofloxacin is a second-generation fluoroquinolone antibiotic with broad-spectrum activity, particularly against Gram-negative bacteria including Pseudomonas aeruginosa. 1
Antibiotic Class and Generation
Ciprofloxacin belongs to the fluoroquinolone class of antimicrobial agents, which are structurally related to nalidixic acid but enhanced by the addition of 6-fluoro and 7-piperazino substituents 2. Specifically, it is classified as a second-generation fluoroquinolone that was introduced in 1987 following the fluorination of quinolone compounds 3.
Mechanism of Action
The primary mechanism of action is inhibition of bacterial DNA gyrase (topoisomerase II) and topoisomerase IV, which are enzymes essential for bacterial DNA replication, transcription, repair, and recombination 4, 5. This mechanism is distinct from penicillins, cephalosporins, aminoglycosides, macrolides, and tetracyclines, meaning bacteria resistant to those classes may remain susceptible to ciprofloxacin 4.
Antimicrobial Spectrum
Gram-Negative Coverage
Second-generation fluoroquinolones like ciprofloxacin have a greater Gram-negative spectrum, including Pseudomonas aeruginosa, which distinguishes them from first-generation agents 1. The drug demonstrates potent activity against:
- Enteric Gram-negative bacteria (E. coli, Klebsiella, Proteus, Enterobacter) 4
- Pseudomonas aeruginosa 4, 2
- Haemophilus influenzae 4
- Neisseria gonorrhoeae 4
- Salmonella and Shigella species 4
Gram-Positive Coverage
Ciprofloxacin has activity against Gram-positive organisms, though it is generally less potent than against Gram-negatives 6. It covers methicillin-susceptible Staphylococcus aureus and Streptococcus pneumoniae (penicillin-susceptible strains), but should not be considered first-line for respiratory infections where penicillin-susceptible S. pneumoniae is the primary pathogen 3, 6.
Important Limitations
- Most anaerobic bacteria are resistant, including Bacteroides fragilis and Clostridium difficile 4
- Most strains of Burkholderia cepacia and some Stenotrophomonas maltophilia are resistant 4
- High-level penicillin resistance in pneumococci can be associated with ciprofloxacin resistance 3
Clinical Context
Ciprofloxacin is notably less active than third- and fourth-generation fluoroquinolones (like moxifloxacin and gatifloxacin) against Streptococcus pneumoniae, with MIC values ranking it as the least active among newer fluoroquinolones for pneumococcal coverage 3. This is a critical distinction when selecting empiric therapy for community-acquired pneumonia, where ciprofloxacin would not be the preferred fluoroquinolone choice 3.
The drug is available in both oral and intravenous formulations, achieving therapeutic concentrations in most tissues and body fluids 4, 6. This allows for sequential IV-to-oral therapy and potential early hospital discharge in appropriately selected patients 6.