April 27, 2017
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Mechanism of Action

Ciprofloxacin is a fluoroquinolone antimicrobial (see CLINICAL PHARMACOLOGY, Microbiology).


The plasma concentrations of ciprofloxacin were not measured following administration of 0.25 mL CETRAXAL (total dose: 0.5 mg ciprofloxacin). However, the maximum plasma concentration of ciprofloxacin is anticipated to be less than 5 ng/mL.


The bactericidal action of ciprofloxacin results from interference with the enzyme DNA gyrase, which is needed for the synthesis of bacterial DNA.

Bacterial resistance to quinolones can develop through chromosomally- or plasmidmediated mechanisms.

The mechanism of action of fluoroquinolones, including ciprofloxacin, is different from that of macrolides. Therefore, ciprofloxacin may be active against pathogens that are resistant to these antibiotics, and these antibiotics may be active against pathogens that are resistant to ciprofloxacin. In vitro studies demonstrated cross-resistance between ciprofloxacin and some fluoroquinolones.

Ciprofloxacin has been shown to be active against most isolates of the following bacteria, both in vitro and in clinical infections of acute otitis externa as described in INDICATIONS AND USAGE:

Staphylococcus aureus
Pseudomonas aeruginosa.

Clinical Studies

In a randomized, multi-center, evaluator-blinded study of patients with acute otitis externa, patients were treated with either CETRAXAL (ciprofloxacin otic solution) twice daily or neomycin and polymyxin B sulfates and hydrocortisone otic solution (PNH) three times daily for 7 days.

In the per protocol population, clinical cure was achieved at the end of a 7-day treatment in 70% (173/247) for the CETRAXAL (ciprofloxacin otic solution) treated group versus 60% (147/243) for the control treated group.

Last reviewed on RxList: 12/8/2016
This monograph has been modified to include the generic and brand name in many instances.

Report Problems to the Food and Drug Administration


You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

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