Fluoroquinolone block DNA synthesis by bacteria (uniquely among antibiotics).
Good against gram negatives, including Salmonella, Shigella, Neisseria, Pseudomonas. Good intracellular penetration so active against organisms such as Chlamydia, Mycoplasma, Legionella and some Mycobacteria. But no anti-anaerobic activity, and not very good against common gram positives eg Pneumococcus, Enterococcus, Staphylococcus. The newer types (gatifloxacin, moxifloxacin, levofloxacin) have better gram positive activity but would still not be your first line choice, and have less antipseudomonal activity.
Good tissue penetration including central nervous system. 80% of orally administered drug is bioavailable so the IV route is only used when absorption impaired.
- Myasthenia gravis (may precipitate initial diagnosis)
- Seizures (+/- predisposing condition)
- Arthropathy in immature animals - so avoided in children (except nalidixic acid) unless extenuating circumstances (only reversible musculoskeletal symptoms have been reported)