Fluoroquinolones — MOA & Use
Fluoroquinolones kill bacteria by targeting their DNA machinery — but their broad-spectrum power comes with strict rules about which clients actually warrant them. Knowing when they're first-line versus last-resort changes the answer.
Core Concept
Fluoroquinolones (ciprofloxacin, levofloxacin, moxifloxacin) work by inhibiting bacterial DNA gyrase and topoisomerase IV — enzymes bacteria need to uncoil and replicate their DNA. Without these enzymes, bacterial DNA fragments and the organism dies. This mechanism makes them bactericidal, not just bacteriostatic. They cover a broad spectrum: gram-negative organisms (E. coli, Pseudomonas for cipro), atypical pathogens (Mycoplasma, Legionella), and respiratory gram-positives (Streptococcus pneumoniae for levofloxacin and moxifloxacin, often called 'respiratory fluoroquinolones'). Key indications include complicated UTIs, hospital-acquired pneumonia, anthrax prophylaxis, and certain bone/joint infections. However, the FDA reserves fluoroquinolones for infections without safer alternatives — they are NOT first-line for uncomplicated UTIs or sinusitis. Generally avoid in pregnancy and clients under 18 due to risk of cartilage damage. Oral bioavailability is excellent, nearly equal to IV, which is why oral-to-IV conversion is common. Absorption is significantly reduced by divalent and trivalent cations: calcium, magnesium, iron, aluminum, and zinc bind to the drug in the gut, forming insoluble complexes. Administer fluoroquinolones 2 hours before or 6 hours after these products, including antacids, dairy, and multivitamins.
Watch Out For
Don't confuse ciprofloxacin (strongest gram-negative and Pseudomonas coverage) with levofloxacin/moxifloxacin (better respiratory and gram-positive coverage). Students often pick fluoroquinolones as first-line for simple UTIs — the NCLEX expects you to know they're reserved for complicated or resistant cases. Unlike aminoglycosides, fluoroquinolones have excellent oral absorption, so IV is not required for adequate tissue levels.
Clinical Pearl
Antacids, dairy, iron, multivitamins — anything with a metal cation eats your fluoroquinolone dose. Separate by 2 hours before or 6 hours after, no exceptions.
Test Your Knowledge
3 quick questions — see how well you understood Fluoroquinolones — MOA & Use