Quinolones specifically inhibit the enzyme DNA gyrase, which is responsible for supercoiling and nicking bacterial DNA. Absence of DNA supercoiling is thought to cause cell death. In Gram-positive bacteria, topoisomerase IV is the main target of quinolones; in Gram-negative bacteria, DNA gyrase is main target.
Resistance may develop during therapy via mutations in the bacterial chromosomal genes encoding DNA gyrase or topoisomerase IV. Quinolones have a good absorption and distribution, and are cleared by the kidneys. Besides some GI complaints, headache, and dizziness, these drugs are well tolerated.
Quinolones are often drug of choice for treatment of Pseudomonas infections. Furthermore, they are applied in urinary tract infections, prostatitis, sexual transmitted diseases, and GI infections. Fluoroquinolones (ciprofloxacin, levofloxacin) are effective (bactericidal) against: E. coli, Legionella, Mycoplasma, Salmonella, Shigella, Enterobacter, Campylobacter, and Neisseria.
Fluoroquinolones exhibit concentration-dependent killing of bacteria
Extra info: Maintenance of minimum-inhibitory-concentrations are required for effectiveness.
Ciprofloxacin is NOT active against aerobic Gram-negative bacteria.
Extra info: The spectrum of ciprofloxacin mainly covers Gram-negative bacteria.
Fluoroquinolones have excellent oral bioavailability.
Extra info: Oral dosing of fluoroquinolones is thus recommended.
Ciprofloxacin is the drug of choice in children with osteomylitis.
Extra info: Indeed for osteomylitis ciprofloxacin is indicated, but in children younger than 16 years ciprofloxacin is contraindicated due to disturbance in collagen formation.