Fluoroquinolones are bactericidal drugs that block bacterial DNA synthesis by inhibiting DNA gyrase (topoisomerase). Fluoroquinolones, such as ciprofloxacin (Figure 1), levofloxacin, norfloxacin, ofloxacin, and others, are active against a broad range of organisms that cause infections of the lower respiratory tract, intestinal tract, urinary tract, and skeletal and soft tissues. Nalidixic acid, which is a quinolone but not a fluoroquinolone, is much less active and is used only for the treatment of UTIs. Fluoroquinolones should not be given to pregnant women and children under the age of 18 years because they damage growing bone and cartilage.
Fig1. Ciprofloxacin. The triangle indicates a cyclopro pyl group.
In 2018, the FDA approved delafloxacin for the treatment of acute bacterial skin and soft tissue infections. Delafloxacin is a fluoroquinolone that is effective against gram-positive cocci, like S. aureus, S. pyogenes, and E. faecalis. It is effective against gram-negative bacteria, for example, E. coli, Klebsiella, Pseudomonas, and Legionella. It is also effective against Mycoplasma and anaerobes such as Bacteroides. It is the only fluoroquinolone approved for the treatment of MRSA.
The FDA issued a warning regarding the possibility of Achilles tendonitis and tendon rupture associated with fluoroquinolone use, especially in those over 60 years of age and in patients receiving corticosteroids, such as prednisone. The FDA recommends that fluoroquinolones not be used in the treatment of acute sinusitis and uncomplicated UTIs. Fluoroquinolones can also cause peripheral neuropathy, the symptoms of which include pain, burning, numbness, or tingling in the arms or legs. Another rare but serious adverse effect is rupture of the aorta.
