Pharmacology · Class
Fluoroquinolones !
Bactericidal antibiotics that trap DNA gyrase and topoisomerase IV on cut DNA. Powerful, but with tendon, nerve and QT warnings.
Updated 2026-11-01
What they are
Synthetic antibiotics (ciprofloxacin, levofloxacin, moxifloxacin, ofloxacin) that kill bacteria quickly and are very well absorbed by mouth. Ciprofloxacin is strongest against gram-negatives such as Pseudomonas; levofloxacin and moxifloxacin, the «respiratory» quinolones, also cover pneumococcus.
Mechanism of action
They bind the complex of DNA with DNA gyrase (mainly in gram-negatives) or topoisomerase IV (mainly in gram-positives) after the enzyme has cut both strands. The enzyme is trapped on broken DNA, replication forks collide with it and the double-strand breaks kill the cell. Resistance comes from mutations in gyrA/parC, efflux and plasmid qnr genes.
Target: Bacterial DNA gyrase and topoisomerase IV (type II topoisomerases)
Drugs in this class
- CiprofloxacinThe fluoroquinolone most active against gram-negatives such as Pseudomonas. Used for kidney, prostate and gut…Bacterial DNA gyrase and topoisomerase IV
- LevofloxacinA «respiratory» fluoroquinolone that covers pneumococcus and atypical bacteria, fully absorbed by mouth and also used…Bacterial topoisomerase IV and DNA gyrase
- MoxifloxacinA respiratory fluoroquinolone with anaerobic activity, cleared mostly by the liver. A WHO medicine for drug-resistant…Bacterial DNA gyrase and topoisomerase IV
- OfloxacinA fluoroquinolone mostly used today as eye and ear drops. Its active half, levofloxacin, replaced it for systemic use.Bacterial DNA gyrase and topoisomerase IV
Others in the class
- norfloxacin
- delafloxacin
- gemifloxacin
Test yourself
Think of the answer, then tap the question to see it.
What do fluoroquinolones trap?
DNA gyrase or topoisomerase IV bound to DNA that has been cut, producing lethal double-strand breaks.
Which musculoskeletal adverse effect is in the boxed warning?
Tendinitis and tendon rupture, especially of the Achilles tendon.
Why are fluoroquinolones spaced from antacids?
Aluminium, magnesium, calcium and iron chelate them and sharply reduce absorption.
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - CIPROFLOXACIN tablet, film coated (DailyMed (U.S. National Library of Medicine), 2026); DailyMed - LEVOFLOXACIN tablet, film coated (DailyMed (U.S. National Library of Medicine), 2026); DailyMed - MOXIFLOXACIN HYDROCHLORIDE tablet, film coated (DailyMed (U.S. National Library of Medicine), 2026); eEML - Electronic Essential Medicines List (World Health Organization, 2025).
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Representative model, for educational purposes only.